Basic refrigeration system & practice theory book

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Chapter: 1
Fundamentals of Refrigeration
And
Introduction to Thermodynamic
1 Fundamentals of Refrigeration
And Introduction to Thermodynamic
 Fundamentals of Thermodynamic
 Understand the General Refrigeration
Safety
 Tools and Procedures and Rules in
Trade Areas
 Types of Strength of Metals
Definition of Refrigeration
The term “Refrigeration” may be defined as the process of removing heat from a substance
under controlled conditions. It also includes the process of reducing
and maintaining temperature of a body under below the general temperature of its
surroundings. In other words, the refrigeration means a continued extraction of heat from a
body whose temperature is already below the temperature of its surroundings.
SI Units (International System of Units)
In this system of units, there are seven fundamentals units and two supplementary units, which
cover entire field of science and engineering.
There are some derived units which will be commonly used.

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Photo- Refrigeration and Air conditioning- RS Khurmi
Thermodynamic System
The thermodynamic system (or simply known as “system”) may be broadly defined as a
“definite area” or “space” where some thermodynamic process takes place. A thermodynamic
system has its boundaries and anything outside the boundaries is called its surrounding (Fig.
1.1).

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Thermodynamic system may be classified into three groups-
1. Closed System; 2. Open System; 3. Isolated System.
1. Closed system- This is a system of fixed mass and identity whose boundaries are determined by
space of matter (working substance) occupied in it (Fig. 1.2).
2. Open system-
In the open system, the mass of working substance crosses the boundary of system (Fig. 1.3).

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3. Isolated system-
A system is completely uninfluenced by surrounding called is an isolated system.
Temperature
The temperature of a body is measured with the help of an instrument known as thermometer
which is in a form of glass tube containing mercury in its stem.
Following are the two commonly used scales to measure the temperature-
1. Celsius or Centigrade scale
Freezing point of water on scale is marked as zero and boiling point of water is marked as 100.
The space between these two points has 100 equal divisions and each division represents one
degree Celsius (1°C).

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2. Fahrenheit scale
In this scale, freezing point of water on scale is marked as 32 and boiling point of water is
marked as 212. The space between these two points has 180 equal divisions and each division
represents one-degree Fahrenheit (1°F).
Note. - Relation between Celsius scale and Fahrenheit scale.
C = F – 32
100 180

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Kelvin
The Kelvin, commonly called the degree Kelvin (o K). One kelvin is formally defined as 1/273.16
of the thermodynamic temperature of the triple point of pure water (H2O). A temperature of 0
K represents absolute zero, the absence of all heat.
Rankine
Rankine scale same works as Fahrenheit scale on which the freezing point of water 491.67 ° and
the boiling point is 671.67°.
Temperature Conversion Formula
Degree Celsius (°C) (°F - 32) x 5/9
(K - 273.15)
Degree Fahrenheit (°F) (°C x 9/5) + 32
(1.8 x K) - 459.67
Kelvin (K) (°C + 273.15)
(°F + 459.67) ÷ 1.8
Some Useful Engineering Definitions and Units
Pressure: Force exerted per unit area is called pressure. Pressure is defined as:
P = F/A
Where P = Pressure in Pascals (Pa)
1 Pascal = 1N/ m2
F = Force in N
A = Area in m2
1 Bar = 105 Pa
= 1.02 kgf/cm2
= 14.5 lbf/sq. in.
1 psig = 6894 Pa
= 0.068 Bar
At sea level, atmosphere exerts a force of 101325 N on one square meter area.
1 Atm. pressure = 101325 N/m
= 1.01325 Bar
= 1.033 kg f/m2
= 14.896 lbf/sq. in.

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Work or Energy: Force applied to a body to move it to a distance is called work.
Work = Force × Distance
Unit of work or energy in S.I. units is Nm or Joule (J).
i.e. 1 Nm = 1 J
If a force of 1N moves a body by 1m, it is called work of 1J or 1 Nm is done.
In M.K.S. Work/energy = kgf m
In case of heat energy in MKS, it is called k cal. Conversion of heat energy into work is by
mech equivalent of heat (J).
1 k cal = 427 Kgf m
In F.P.S., unit of heat is British Thermal Unit (BTU))
1 k cal = 4.19 kJ = 3.968 BTU
Power: Rate of doing work is called power. Unit of power in S.I. is Watts (W).
1 Watt = 1 J/s
Electrical unit of work is also Watt
i.e. 1 Watt = 1 amp × 1 volt = 1J/sec.
In F.P.S. System, unit of power is Horse Power (H.P. imperial).
1 H.P. (Imperial) = 550 Ft lb/s
= 746 J/s
= 746 W
In M.K.S. System, unit of power is H.P. (metric)
1 H.P. (metric) = 75 Kgf m/s
= 736 J/s
= 736 W
5.Unit of energy or work can also be derived from power
W = J/sec
∴ J = W × sec
Now, kWh is the unit of work
1 kWh = 3600 kJ.
Common Conversion Factors:
1 k cal = 3.968 BTU = 4.187 kJ
1 kJ = 0.239 k cal
1 kJ = 0.948 BTU

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1 BTU = 0.252 k cal
1 BTU = 1.055 kJ
1 k cal/h = 1.163 W
1 kW/h = 3.968 BTU/h
1 H.P. (imperial) = 642 k cal/h
(H.P. normally refers to H.P. imperial. Unless specified as H.P. metric).
1 H.P. = 2546.4 BTU/h
Heat Flux 1 k cal/hm2 = 1.163 W/m2
= 0.3687 BTU/h ft2.
Gauge pressure and Absolute Pressure
All the pressure gauges read the difference between the actual pressure in system and
atmospheric pressure(P0). The reading of pressure gauge is known as gauge pressure(Pg), while
the actual pressure is called absolute pressure(P).
Mathematically, P= P0 + Pg
The negative gauge pressure is known as Vacuum Pressure.
Absolute Pressure = Gauge Pressure + Atmospheric Pressure
Vacuum Pressure = Atmospheric Pressure- Absolute Pressure

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Gauge pressure is measured as PSIG (Pound/square inch gauge).
Note: Atmospheric Pressure = 14.7 psi (The absolute air pressure at sea level is about 14.7 psi.)
The unit of pressure in the SI system is the pascal (Pa), defined as a force of one Newton per
square meter
Heat
The heat is defined as the transfer of energy without transfer of mass across the boundary of
system because of the temperature difference between the system and surrounding. It is
represented by Q and unit is Joule.
They can be transferred in three distinct ways i.e., conduction, convection and radiation.
The heat transferred through solid called conduction, while the heat transferred through fluid
called convection. The radiation is an electromagnetic wave phenomenon in which energy can
be transported through the electromagnetic waves.
Gauge Pressure = Absolute Pressure - Atmospheric Pressure
PSIG (Gauge Pressure) = PSI (Absolute Pressure) - Atmospheric Pressure
(14.7 PSI)

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Sensible heat
When a substance is heated and temperature rises as the heat is added, the increase in heat is
called sensible heat. Similarly, when the heat is removed and temperature falls, the heat
removed (subtracted) is called sensible heat.
Latent Heat
All pure substances are able to change their states. Solid become liquids and liquids become
gas. These changes of state occur at same temperature and pressure combination for any given
substance. It takes the addition of heat or removal of heat to produce these changes. The heat
which brings about a change of state with no changes in temperature is called is called Latent
(hidden) heat.
Specific heat
The specific heat of a substance may be broadly defined as the amount of heat required to raise
the temperature of a unit mass of any substance through one degree.

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Law of Perfect Gases
A perfect gas (or an ideal gas) may be defined as a state of substance whose evaporation from
its liquid state is complete and strictly obey the all the gas law under all condition of
temperature and pressure.
Boyle’s law
This law was formulated by Robert Boyles in 1662. It states “The absolute pressure of a given
mass of a perfect gas varies inversely as its volume, when the temperature remains constant.”
Mathematically,
P ∝ 1 or
v
Charles’ Law
This law was formulated by Frenchman Jacques AC Charles in 1787. It states
(1) “The volume of a given mass of a perfect gas varies directly as its absolute temperature, when
the absolute pressure remains constant.”
v ∝ T or v = constant
T
So,
(2) “All the perfect gases change in volume by 1/273th of its original volume at 0° C for every 1°
change in temperature, when the pressure remains constant.”
pv1 = pv2= pv3 = constant
v1 = v2 = constant
T1 T2
pv = constant

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Pressure Temperature chart
During the repairing of refrigerators, air conditioners and other machines that contain
refrigerant gas, we use pressure temperature chart (PT chart). PT chart show the relationship
between pressure and temperature for the given refrigerant.
By changing the pressure of refrigerant, we can set its temperature to a given level.
How to read a PT chart
1. Turn unit on; monitor system running approx. 15 to 30 minutes. Take a reading of your
refrigerant system pressure at suction line (psig).
2. Find the corresponding saturated pressure for your refrigerant.
Saturation
Saturated liquid- When the temperature of a fluid is raised to the saturated temperature, that
is, any additional heat applies to the liquid will cause a part of the liquid to vaporize, the liquid
is said to be saturated. That liquid is called saturated liquid while the process is called
Saturation.
Saturated vapor- When the temperature of a vapor is decreased to the saturation temperature,
that is any further cooling of the vapor will cause a portion of vapor to the condense, the vapor
said to be saturated. Such a vapor called a “saturated vapor”.
A saturated vapor may be described also as a vapor ensuring from the vaporizing liquid as long
as temperature and pressure of the vapor are the same as those of saturated liquid from which
it comes.
Superheat
Superheated vapor- When the temperature of a vapor is so increased above the saturation
temperature, the vapor is said to be superheated and is called a “superheated vapor”.
In order to superheat it is necessary to separate the vapor from vaporizing liquid. As long as the
vapor remains in contact with liquid it will be saturated. This is because any heat added to
liquid-vapor mixture will merely vaporize more liquid and no superheating will occur.
Sub cooling
Sub-Cooled liquid -If after condensation, a liquid is cooled so that its temperature is reduced
below the saturation temperature the liquid is said to be “sub-cooled”. A liquid at any
temperature and above the melting temperature is a sub-cooled liquid.

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Heat Load
The rate at which the heat must be removed from the refrigerated space or material in order to
produce and maintain desired temperature condition is called the heat load.
In most refrigerating applications, the total heat load on the refrigerating equipment is the sum
of the heat that leaks into the refrigerated space through the insulated walls, the heat that
enters the space through door opening and the heat that must be removed from the
refrigerated product in order to reduce the temperature of product to the space or storage
conditions.
Heat given off by the people working in the refrigerated space and by motors, light and other
electrical equipment’s also contributes the load on the refrigerated equipment.

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Four factor Affecting Comfort Air
Temperature
When you talk about the weather, what’s the first factor you define? temperature. “It’s hot
out.” “It’s cool and cloudy.” But temperature isn’t inherently stable. A room with the perfect
temperature is in a constant struggle with external factors.
Sunlight coming through a window adds heat. A draft coming in under the door lets heat
escape. Even your own body can affect the temperature in a room. (The average human
generates as much heat as a 100-watt light bulb). So, a comfortable temperature isn’t just about
getting there, it’s about maintaining. It’s by far the most influential to your comfort. And it’s the
only factor that most conventional thermostats let you control.

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Humidity
It’s not the heat, it's… yes, and it’s the humidity, which can have a huge impact on how your
room feels. Second only to temperature in its ability to affect comfort, humidity does more
than most people realize. Humidity is made up of tiny water droplets in the air. And while these
droplets are incredibly small, they can still prevent your body’s natural cooling response –
sweating – from being nearly as effective. After all, moisture from your skin can’t evaporate
(taking heat with it) if it has no place to go.
Humid air also feels heavier and stickier, both of which add to the discomfort you feel on a hot
day. In fact, humidity can affect the “felt temperature” by as much as 8 degrees, even if the
actual temperature doesn’t change at all.
Air quality
A room with dirty air doesn’t feel as good. Airborne impurities can irritate eyes, noses and
lungs, and create odors that make any space uncomfortable. There are three main offenders
when it comes to air quality:
Particles - made up of dust, dirt, pet dander and allergens, such as pollen
Mold, Mildew and Germs - the tiny organisms floating in your air that thrive in damp
environments and greatly exacerbate allergies and asthma.
Chemical Vapors and Odors - generated by cleaning products, paint, adhesives and other
chemicals found in nearly every home Filtration can take care of some of these pollutants,
however, a UV germicidal light can add an extra layer of protection for the cleanliness, and
comfort, of your air.

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Control
Obviously, if humidity, temperature and air quality can change the way your environment feels,
the ability to control those three factors is pretty important.
Having the right home heating and air-conditioning system, controlled by the proper
thermostat, will let you create and preserve your perfect indoor space.
Conventional thermostats let you control the temperature, and that’s a good start.

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A. Refrigeration Tools
1. Tube Cutter- A tube cutter is a type of tool used by technician to cut copper pipe. Besides
producing a clean cut, the tool is often a faster, cleaner, and more convenient way of cutting
pipe than using a hacksaw, although this depends on the metal of the pipe.
2. Flaring Tool-
Flaring tool is to make flares at end of copper tube as could be easily fit in the flare nut without
any leakage of refrigerant.
3. Swaging Tool
Swaging is the process to increase the diameter of any copper pipe with the help of swaging
tool.
Swaging tool is often called punching tool also.
4. Bending Tool-
Bending tool is used for make different types of bend in copper pipes as the requirement of
side position. We can use bending machine as well as spring to make bend in copper pipes.

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5. Pinch off Tool
Pinch off tool is used to pinch off service line or any other copper line in order to make the
sealed system.
6. Gauge Manifold
Manifold gauge is often used to measure the gas vapor or liquid pressure or vacuum pressure
inside the system.

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7. Vacuum Pump
The purpose of a vacuum pump is to remove the undesirable materials that create pressure in a
refrigeration system such as moisture, dust and dirt inside the coil.
These include:
• Moisture
• Air (oxygen)
• Hydrochloric acid

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8. Refrigerant Recycling Station
Laws governing the release of chlorofluorocarbon refrigerants (CFCs) into the atmosphere have
resulted in the development of procedures to recover, recycle, and reuse these refrigerants.
Removing refrigerant from a system in any condition and storing it in an external container is
called "recovery." The process of cleaning refrigerant for reuse by oil separation and single or
multiple passes through filter-driers which reduce moisture, acidity, and matter is called
"recycling."
9. Electronic leak detector
Electronic leak detector equipment’s are the equipment which detects the leakage of gas by
halogen leak detector method in halogen leak detector is work on the concept of halogen gas
(Inert Gas) method.

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10. Thermometer
A thermometer is a device that measures temperature or a temperature gradient. A
thermometer has two important elements:
(1) A temperature sensor (e.g. the bulb of a mercury-in-glass thermometer or the digital sensor
in an infrared thermometer) in which some change occurs with a change in temperature, and
(2) Some means of converting this change into a numerical value (e.g. the visible scale that is
marked on a mercury-in-glass thermometer or the digital readout on an infrared model).
Thermometers are widely used in industry to monitor processes, in meteorology, in medicine,
and in scientific research.
11. Fin Comb
Fin comb or fin straightener are used to straight the fins as it can make the proper rotation of
cooling air through the fins.
12. Hermetic Tubing Piercing Valve
Hermetic tubing Piercing Valve is often used for a non-soldier piercing valve that works very
well. Simply follow the enclosed instructions. The only tip I would give would be to tighten the
screws until they are very firm to prevent leaks.

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13. Compressor Oil Charging Pump
Whenever it is impossible to drain oil in the conventional manner, it becomes necessary to
hook up a pump. Removing oil from refrigeration compressors before dehydrating with a
vacuum is a necessity. The pump shown in Fig. has the ability to remove one quart of oil with
about 10 strokes. It is designed for use in pumping oil from refrigeration compressors, marine
engines, and other equipment.
15. Air velocity meter
Air Velocity Meters measure air velocity and temperature, calculate flow rate and perform
statistical calculations. Some models also measure humidity and perform dew point and wet
bulb temperature calculations.
16. Volt-ohm meter
A VOM (volt-ohm-millimeter), is also known as a multi-meter or a multi-tester, it is
an electronic measuring instrument that combines several measurement functions in one unit.
A typical VOM can measure voltage, current, and resistance. Analog VOM use a micro-
ammeter with a moving pointer to display readings. Digital VOM (DMM, DVOM) have a numeric
display, and may also show a graphical bar representing the measured value.

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17. AC Clamp on meter
AC clamp meter are widely used to measure the ampere, voltage and resistance and also to
check diode and continuity on different sets.
18. U-Tube manometer
It is one of the earliest pressure measuring instruments is still in wide use today because of its
inherent accuracy and simplicity of operation. U-tube manometer, which is a U-shaped glass
tube partially filled with liquid. This manometer has no moving parts and requires no
calibration. Manometry measurements are functions of gravity and the liquid's density, both
physical properties and it is used to measure absolute pressure.
The fundamental relationship for pressure expressed by a liquid column is:
Δp = P2-P1 = ρgh

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where: Δp = differential pressure
P1= pressure at the low-pressure connection
P2= pressure at the high-pressure connection
ρ = density of the indicating fluid (at a specific temperature)
g = acceleration of gravity (at a specific latitude and elevation)
h = difference in column heights
20. Refrigerant Charging Hose
Refrigerant charging hose are used when the system needs gas charging, vacuuming and
nitrogen pressure holding. These refrigerant charging hoses are designed with a special
material for bearing high pressure.

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21. Ratchet Wrench
Ratchet wrench are used to general operation of machine, these are reversible type wrench.
22. Pin Valve
Pin valve or service valve is used for gas charging or vacuuming of refrigeration system. Pin
valve allows the refrigerant to enter in the system and make it enclosed within the system.

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Chapter: 2
Introduction to Strength of Material
STRENGTH
Strength is the ability of the structure to resist the influence of the external forces acting upon
it.
1. TENSILE STRENGTH
The tensile strength of a material is the maximum amount of tensile stress that it can take
before failure, such as breaking or permanent deformation. Tensile strength specifies the point
when a material goes from elastic to plastic deformation.
2. COMPRESSIVE STRENGTH
Compressive strength is the maximum compressive stress that, under a gradually applied load,
a given solid material can sustain without fracture.
3. SHEAR STRENGTH
Shear strength is a material's ability to resist forces that can cause the internal structure of the
material to slide against it. Adhesives tend to have high shear strength.

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4. BENDING STRENGTH
Flexural strength is a measure of the tensile strength of concrete beams or slabs. Flexural
strength identifies the amount of stress and force an unreinforced concrete slab, beam or other
structure can withstand such that it resists any bending failures.
Flexural strength is also known as bend strength or modulus of rupture or fracture strength.
Elastic and Plastic behavior
 All materials deform when subjected to an external load.
 Up to a certain load the material will recover its original.
Dimensions when the load is released. This is known as elastic behavior.
 The load up to which the material remains elastic is the elastic limit. The deformation or strain
produced within the elastic limit is proportional to the load or stress.
This is known as Hook’s Law Stress  Strain or Stress = E*Strain.
E is known as the Elastic Modulus.
 When the load exceeds the elastic limit, the deformation produced is permanent. This is called
plastic deformation. Hook’s law is no longer valid in the plastic region.

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Chapter: 3
Basic Refrigeration System and Applications
2 Basic Refrigeration Systems & Practice  Refrigeration Processes and
Components of Domestic Freezers,
Water Coolers and Ice Cream
Machines
Refrigeration
A refrigeration system moves heat from a space, fluid or material for the purpose of lowering
its temperature. In the past, this was done by collecting ice in the winter and using its specific
heat to cool as the ice melted. When 1 pound of ice melts, it absorbs 144 Btu, as latent energy.
When 1-ton (2000 lbs) melts over a 24-hour period:
Q = 2000 lbs × 144 Btu/lb/24 hrs = 12,000 Btu/h
This is the definition of 1 ton of refrigeration.

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Components of Refrigeration System
There are four main parts of refrigerating and air-conditioning systems, these
are: compressor, condenser, throttling or expansion valve and the evaporator.
The refrigerant leaving the compressor is in the gaseous state and at a high pressure and
temperature. This refrigerant then enters the condenser where it loses the heat to the coolant,
which can be air or water.
Evaporator
An evaporator coils inside the refrigerator allow the refrigerant to absorb heat, making the
refrigerator cabinet cold.
Types of Evaporators
The evaporators can be classified in various ways depending on the construction of the
evaporator, the method of feeding the refrigerant, the direction of circulation of the air around
the evaporator, etc. Here we have classified the evaporators based on their construction.
1) Bare Tube Evaporators
The bare tube evaporators are made up of copper tubing or steel pipes. The copper tubing is
used for small evaporators, while the steel pipes are used with the large evaporators where
ammonia is used as the refrigerant. The bare tube evaporator comprises of several turns of the
tubing, though most commonly flat zigzag and oval trombone are the most common shapes.
The bare tube evaporators are usually used for liquid chilling.
2) Plate Type of Evaporators
In the plate type of evaporators, the coil usually made up of copper or aluminum is embedded
in the plate so as so to form a flat looking surface. Externally the plate type of evaporator looks
like a single plate, but inside it there are several turns of the metal tubing through which the
refrigerant flows.
3) Finned Evaporators
The finned evaporators are the bare tube type of evaporators covered with the fins. When the
fluid (air or water) to be chilled flows over the bare tube evaporator lots of cooling effect from

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the refrigerant goes wasted since there is less contact of surface for the transfer of heat from
the fluid to the refrigerant.
4) Shell and Tube types of Evaporators
The shell and tube types of evaporators are used in the large refrigeration and central air
conditioning systems. The evaporators in these systems are commonly known as the chillers.
The chillers comprise of large number of the tubes that are inserted inside the drum or the
shell. Depending on the direction of the flow of the refrigerant in the shell and tube type of
chillers, they are classified into two types: dry expansion type and flooded type of chillers. In
dry expansion chillers the refrigerant flows along the tube side and the fluid to be chilled flows
along the shell side. The flow of the refrigerant to these chillers is controlled by the expansion
valve. In case of the flooded type of evaporators the refrigerant flows along the shell side and
fluid to be chilled flows along the tube. In these chillers the level of the refrigerant is kept
constant by the float valve that acts as the expansion valve also.
5) Natural Draught Evaporator
Natural draught or ribbed-tube evaporator are used because cold air is denser than warm air,
he falls without the help of a blower. Warm air rises up to take his place. Thus, this type of coil
is mounted vertically on a high wall, or horizontally just below the ceiling space, it cools. Since
the flow of air through natural draught, coils easily interfered with, the fins are far from each
other and the number of coil line, as a rule, is limited to three or less. Evaporators are set such
that they cover most of the length of the space cooling. This type of evaporator is typically used
in refrigerated display cases, florist boxes.

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Compressor
Compressors are mechanical devices that compress gases. It is widely used in industries and has
various applications.
Compressors have many everyday uses, such as in:
 Air conditioners (car, home)
 Home and industrial refrigeration
 Hydraulic compressors for industrial machines
 Air compressors for industrial manufacturing
Condenser
The condenser helps in rejection of heat to the surroundings. In the condenser, the refrigerant
cools down and is condensed to liquid.
There are three main types of condensers:
1) Air cooled condensers: Air cooled condensers are used in small units like household
refrigerators, deep freezers, water coolers, window air-conditioners, split air-conditioners,
small packaged air-conditioners etc. These are used in plants where the cooling load is small
and the total quantity of the refrigerant in the refrigeration cycle is small. Air cooled condensers
are also called coil condensers as they are usually made of copper or aluminum coil. Air cooled
condensers occupy a comparatively larger space than water cooled condensers.
Air cooled condensers are of two types: natural convection and forced convection. In the
natural convection type, the air flows over it in natural a way depending upon the temperature
of the condenser coil. In the forced air type, a fan operated by a motor blows air over the
condenser coil.
2) Water cooled condensers: Water cooled condensers are used for large refrigerating plants, big
packaged air-conditioners, central air-conditioning plants, etc. These are used in plants where
cooling loads are excessively high and a large quantity of refrigerant flows through the
condenser.
There are three types of water cooled condensers: tube-in-tube or double pipe type, shell and
coil type and shell and tube type. In all these condensers the refrigerant flows through one side
of the piping while the water flows through the other piping, cooling the refrigerant and
condensing it.
3) Evaporative condensers: Evaporative condensers are usually used in ice plants. They are a
combination of water cooled and air-cooled condensers. In these 0condensers the hot
refrigerant flows through the coils. Water is sprayed over these coils. At the same time the fan
draws air from the bottom side of the condenser and discharges it from the top side of the
condenser. The spray water that comes in contact with the condenser coil gets evaporated in
the air and it absorbs the heat from the condenser, cools the refrigerant and condenses it.
Evaporative condensers have the benefits of water cooled as well as air cooled condenser,
hence it occupies less space. However, keeping the evaporative condenser clean and free of
scale is very difficult and requires lots of maintenance.

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Metering Device
As the liquid refrigerant enters the metering device it changes temperature, pressure and its
phase. A partial amount of the liquid refrigerant flashes into a refrigerant gas or vapor. The
refrigerant does this as it leaves the metering device and enters the evaporator coil.
Metering devices are further classified as in two groups
1. Copper Capillary Tube
Copper capillary tube is often considered as a metering device.
A capillary is a very small aperture tube (small opening) which allows the liquid refrigerant
under high pressure to expand by entering into the low-pressure zone (evaporator); it is
generally used in air conditioner, refrigerator and freezer.
2. Thermal Expansion Valve
A thermal expansion valve is a component in refrigeration and air conditioning systems that
controls the amount of refrigerant released into the evaporator thereby controlling superheat.
Thermal expansion valves are often referred to generically as "metering devices" and generally
used in cold room, refrigerated van and marine refrigeration.
Copper Accumulators
Copper Accumulators hold unused system charge to prevent liquid slugging of the compressor
and excessive refrigerant dilution of the compressor oil.
“Copper accumulators are widely used for liquid storage, liquid/gas separation, impurity
filtration, noise reduction and refrigerant cushion.”
It is always installed at evaporator side.

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Filter/Drier-
It is always installed at condenser side & it absorbs and retain residual moisture in system.

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Defrost & Automatic Defrost
When the air flow is too slow either has completely halted across the cooling coil or the
refrigerant is not being metered properly into the cooling coil, (too little is being released) then
there is an ice formation on the evaporator coils which affects the cooling performance of the
system. Defrost is a process to remove ice from evaporator coil through the defrost heater.
Automatic Defrost is a process in a refrigerator heats the cooling element (evaporator coil) for
a short period of time and melts the frost that has formed on it.
Wiring and Control
Please refer some electrical wiring diagram for Split air conditioner
Fig. Panasonic Split AC electrical wiring Diagram

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Fig. Manufacturer’s Electrical Wiring Diagram

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Compressor Controls-
Capacitor
Single-phase compressors require a technician to have a proficient understanding of capacitors.
The run capacitor is one of two types of capacitors that could be found on single-phase
compressors.
Run Capacitor
The run capacitor is used to improve the running efficiency of a compressor’s motor. The run
capacitor is placed in series with the start winding of the compressor and will remain in the
circuit as the motor operates. As current flows through the run capacitor and the start winding,
it causes a phase shift of the motor’s current, thus improving the power factor of the motor.
Since the run capacitor remains in the circuit.

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Start Capacitor
The start cap provides that electrical "push" to get the motor rotation started. It does this by
creating a current to voltage lag in the separate start windings of the motor. Since this current
build up slower, the armature has time to react to the rotating field as it builds up, and to begin
rotating with the field. Once the motor is very close to its rated speed, a centrifugal switch
disconnects the start cap and start windings from the circuit. Watching a single-phase motor
starting you can see that this all happens very quickly.
Starting Relay
Potential or “voltage” relays are used with single-phase capacitor-start/capacitor-run motors,
which need relatively high starting torque. Their main function is to assist in starting the motor.
Potential starting relays consist of a high resistance coil and a set of normally closed contacts.
The coil is wired between terminals 2 and 5, with the contacts between terminals 1 and 2.
Terminals 4 and 6 is used for capacitors and/or condenser fan connections and has no electrical
significance to the starting relay itself. In fact, terminals 4 and 6 are sometimes referred to as
“dummy” terminals and are simply used for wire connections.

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Overload Protector
An overload protector is an electrical device which we use for compressors protection,
whenever the compressor temperature high from his range the compressor overload cut off
the electric supply from compressor motor that's why we called him thermal overload.
Contacts
Compressor contactors are simply heavy-duty switches that allow it to carry extra amperage
that is used by the compressor while it is running. The contactor is made up of a coil and
typically two contacts for a double contactor and 1 for a single pole contactor.

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Compressor Start Circuit
Compressor start circuits consist of a potential relay with normally closed
contacts and start capacitor. When there is a malfunction of the start circuit, the start capacitor
is usually destroyed. (Relief plug opens on top of capacitor.) The capacitor fails because it is an
intermittent duty capacitor that should only be in the electrical circuit for a very brief moment.
Causes of start circuit failure include low line voltage where the compressor pick up voltage is
too low to energize the potential relay so the capacitor remains in the circuit for too long of a
period of time.

41
Function of accessories:
Accessory Function
Relay To disconnect start winding and / or start capacitor from
circuit
PTCR Same as relay but cost effective
Start Capacitor To increase starting torque of motor
Run Capacitor To increase running torque of motor and to improve power
factor
Overload Protector Protects compressor from over current and high temperature
Procedure to checking Common, Run & Start terminals in motor circuit: -
If in doubt, please follow the simple guides given below
1. Identify the correct compressor motor Terminals—
2. Run – Common (R– C) – Lowest resistance
3. Run – Start (R- S) – Highest resistance
4. Common – Start (C – S) – Intermediate resistance
5. Also, R S = C S + R C & C S is normally 3-4 times resistance of R C.
6. Show diagram of test result-
7.

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1. Effect of the wrong Capacitor on the compressor
Higher MFD capacitor
(THAN SPECIFIED)
High current, high winding temperature, relay
malfunction, Wiring burn out, Starting problem
Higher MFD capacitor
(THAN SPECIFIED)
Low torque, relay malfunction, Wiring burn out,
Starting problem
Low voltage rating Capacitor Bursting
2. Effect of the wrong OLP on the compressor
 Oversized overload protector will not protect compressor.
 Undersized overload protector trips unnecessarily.
3. Effect of the wrong Relay on the compressor
 Start winding may stay in circuit for longer time leading to burn out
 Start capacitor may burst
 Relay contracts may get welded causing motor burn out
4. Effect of the wrong Relay on the compressor
S-R Interchange condition
 There will not be any abnormality seen apparently at 230 V or above.
 Relay will chatter at 190 V or below.
 OLP will trip and cycle
 Star capacitor remains circuit for long time, it may burst
 Motor will burn
5. Electrical accessories Location in Motor circuit-
MOTOR
TYPE
OVERLOAD
PROTECTOR
PTC STARTER CURRENT
RELAY
STRATING
CAP.
RUNNING
CAP.
RSIR YES YES
RSCR YES YES YES
CSIR YES YES YES YES
CSCR YES YES YES YES
6. MOTOR TYPE
RSIR Resistance Start Inductive Run
This type is applied to compressors whose power is small and has low
starting Torque.
This type of motor is suitable for capillary systems where equilibrium
pressure is achieved during starting.
RSCR Resistance Start Capacitive Run
This is similar to RSIR, but a Run Capacitor is connected to the PTC for
higher efficiency.
CSIR Capacitive Start Inductive Run

43
This type of motor is suitable for capillary systems where equilibrium
pressure is not achieved during starting.
Medium and high range refrigerators & freezers where starting
torque required is more use this type of motors.
CSCR Capacitive Start Capacitive Run
This is similar to CSIR model, but a run capacitor is connected for
higher efficiency.
Defrost Cycle, Light
The defrost cycle in refrigeration is divided into medium- temperature and low-temperature
ranges; the components that serve the defrost cycle are different.
1. Medium-Temperature Refrigeration
The medium-temperature refrigeration coil normally operates below freezing and rises above
freezing during the off cycle. The air temperature inside the box will always rise above the
freezing point during the off cycle and can be used for the defrost. This is called off-cycle
defrost and can be either random or planned.
2. Random or Off Cycle Defrost
Random defrost will occur when the refrigeration system has enough reserve capacity to cool
more than the load requirement. When the system has reserve capacity, it will be shut down
from time to time by the thermostat, and the air in the cooler can defrost the ice from the coil.
When the compressor is off, the evaporator fans will continue to run, and the air in the cooler
will defrost the ice from the coil. When the refrigeration system does not have enough capacity
or the refrigerated box has a constant load, there may not be enough off time to accomplish
defrost. This is when it has to be planned.
3. Planned Defrost
Planned defrost is accomplished by forcing the compressor to shut down for short periods of
time so that the air in the cooler can defrost the ice from the coil. This is accomplished with a
timer that can be programmed. Normally the timer stops the compressor during times that the
refrigerated box is under the least amount of load.
4. Hot Gas Defrost
The internal heat method of defrost normally uses the hot gas from the compressor. This hot
gas can be introduced into the evaporator from the compressor discharge line to the inlet of
the evaporator and allowed to flow until the evaporator is defrosted. Apportion of the energy
used for hot gas defrost is available in the system. This makes it attractive from an energy-
saving standpoint.

44
Refrigerator Fan Motor
This conversion is usually obtained through the generation of a magnetic field by means of a
current flowing into one or more coils.

45
Types of Electric Motor
Further it can be categorized on the basis of propulsion of fan blades (size of Fan Blade):
1. Sirocco Fans
Air is sucked in from one side and discharge in the rotating direction. The fans are completely
enclosed in the fan housing.
2. Turbo Fans
It is used for ceiling recessed cassette type of multi flow units. It sucks air from bottom and
discharge to periphery.
3. Cross Flow Fans
These are dedicated to wall-wall mounted type indoor units and have a long narrow structure.
Air is sucked from one side a higher side resistance and discharged to other side lower
resistance.
4. Propeller Fans
The propeller fans are in most common use of outdoor units and called axial flow fans as well.
Air is sucked in and discharge in the direction of rotary shaft. These types of fan provide a small
static pressure, while enables the connection of simple ducts when outdoor units are installed
in balcony.

46
Refrigerator Servicing
Refrigerator service mainly comprises the following steps-
1. Cleaning of Condensing coil.
2. Checking of door gasket.
3. Checking of voltage and current.
4. Checking of electrical wiring and components.

47
5. Checking of cooling inside the cabinet.
6. Checking of thermostat.
7. Refrigerant charging if it is less.

48
Chapter: 4
Copper Tube Handling and Evacuation Theory
3 Basic Refrigeration Systems &
Practice
Knowledge of refrigeration signs and
symbols, diagrams and using them
appropriately
Know how to do the tubing, piping,
system evacuation
Refrigeration Signs and Symbols

50
Purpose of Tubing
The purpose behind the copper tubing is to provide smooth flow of refrigerant from indoor unit
to outdoor unit. Copper tube is used widely as a means of conveyance of refrigerant in air
conditioning and refrigeration. Copper is mostly used because of the following properties:
 Resistant to corrosion
 High level of heat transfer
 Easy Machinability and
 Consumption of less refrigerant
 Copper can handle bigger pressure differences
Types of Copper Tube
Types K, L, M, DWV and Medical Gas tube are designated by standard sizes, with the actual
outside diameter always 1/8-inch larger than the standard size designation. Each type
represents a series of sizes with different wall thicknesses. Type K tube has thicker walls than
Type L tube, and Type L walls are thicker than Type M, for any given diameter. All inside
diameters depend on tube size and wall thickness. Copper tube for refrigeration and air-
conditioning field service (RAC) is designated by actual outside diameter.
"Temper" describes the strength and hardness of the tube. Tube in the soft temper can be
joined by the same techniques and is also commonly joined by the use of flare-type and
compression fittings. It is also possible to expand the end of one tube so that it can be joined to
another by soldering or brazing without a capillary fitting—a procedure that can be efficient.
Tube in both the hard and soft tempers can also be joined by a variety of "mechanical" joints
that can be assembled without the use of the heat source required for soldering and brazing.
Tube Properties
The dimensions and other physical characteristics of Types K, L, M and DWV tube are given in
Tables.
Advantages of Copper Tube
Strong, long lasting, copper tube is the leading choice of modern contractors for plumbing,
heating and cooling installations in all kinds of residential and commercial buildings. The
primary reasons for this are:
1. Copper is economical.
2. Copper is lightweight.
3. Copper is formable.
4. Copper is easy to join.
5. Copper is safe.
6. Copper is dependable.
7. Copper is long-lasting.
8. Copper is 100% recyclable.

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Pressure System Sizing
Designing a copper tube water supply system is a matter of determining the minimum tube size
for each part of the total system by balancing the interrelationships of six primary design
considerations:
1. Available main pressure;
2. Pressure required at individual fixtures;
3. Static pressure losses due to height;
4. Water demand (gallons per minute) in the total system and in each of its parts;
5. Pressure losses due to the friction of water flow in the system;
6. Velocity limitations based on noise and erosion.
Types & Sizes of Copper Tube
Nominal
Pipe Size
inches
O.D.
I.D. Wall Thickness
Type
K* L** M*** DWV**** K L M DWV
¼ 0.375 0.305 0.315 - - 0.035 0.030 - -
3/8 0.500 0.402 0.430 0.450 - 0.049 0.035 0.025 -
½ 0.625 0.527 0.545 0.569 - 0.049 0.040 0.028 -
5/8 0.750 0.652 0.666 - - 0.049 0.042 - -

52
¾ 0.875 0.745 0.785 0.811 - 0.065 0.045 0.032 -
1 1.125 0.995 1.025 1.055 - 0.065 0.050 0.035 -
1-1/4 1.375 1.245 1.265 1.291 1.295 0.065 0.055 0.042 0.040
1-1/2 1.625 1.481 1.505 1.527 1.541 0.072 0.060 0.049 0.042
2 2.125 1.959 1.985 2.009 2.041 0.083 0.070 0.058 0.042
2-1/2 2.625 2.435 2.465 2.495 - 0.095 0.080 0.065 -
3 3.125 2.907 2.945 2.981 3.030 0.109 0.090 0.072 0.045
3.5 3.625 3.385 3.425 3.459 - .120 .100 .083 -
4 4.125 3.857 3.897 3.935 4.009 .134 .114 .095 .058
5 5.125 4.805 4.875 4.907 4.981 .160 .125 .109 .072

53
6 6.125 5.741 5.845 5.881 5.959 .192 .140 .122 .083
8 8.125 7.583 7.725 7.785 - .271 .200 .170 -
*K, thick walled, underground residential, commercial and industrial uses.
**L, medium walled, residential and commercial uses
***M, thin walled, above ground residential and light commercial uses.
****DWV, Drain/Waste/Vent, non-pressurized
Copper Tube Insulation
Copper tube insulation is a type of isothermal material which prevents loss of cooling or gain of
heating to copper tube and external tear and wear of copper tube.
ProcedureofPipeCuttingUsingCutter
A pipe / tube cutter is best option to make a straight cut for copper pipes. It comes in
single blade and an adjustable lever to provide the proper force while cutting.
 Prior to the work, wear safety shoes, gloves and goggles.
 Prepare copper tube, tube cutter, reamer, sand cloth, brush and hacksaw.
 Make measurements to the desired length of the pipe.
 Mark the pipe where cutting is to be done.

54
 Insert the copper pipe inside the cutting tool.
 Hold the pipe properly to produce a good result.
 Adjust the lever until the blade touches the pipe.
 Using a counter clockwise direction, move the pipe cutter by one whole turn until you feel that
the blade is starting to cut the pipe. After that, reverse it by clockwise rotation.
 While on clockwise turning, adjust the lever from time to time until the pipe is completely cut
 By using a reamer, remove the burrs from the inside of the tube. The burrs must be removed
because they restrict the flow of the gas.
 Clean the tube by sand cloth and by brush.
PIPECUTTINGUSINGAHACKSAW
 Priortothework,makesurethatallPPE’sareavailableandisbeingused.PPE’slikesafetyshoesandgogglesshouldbe
used.
 Make measurements to the desired length of the pipe.
 Mark the pipe where cutting is to be done.
 Make the cut at a 90 Degree angle to the tubing.
 A fixture may be used to ensure an accurate cut.
 After cutting, ream the tubing and file the end.
 Remove all the chips and fillings, making sure that no debris or metal particles get into the
tubing.

55
Tube Bending
Several types of tubing benders are available for making accurate bends in tubing without
causing flats, kinks, or dents.
Procedure to Make Bends Using Spring benders
 Spring benders provide an efficient, low-cost method to bend soft copper tubing.
 Spring benders are available in a variety of sizes to fit tubing from 1/4″ OD to 3/4″ OD.
 Mark the area of bend with the help of measuring tape.
 First slip the spring over the tubing to completely cover the area of the bend.
 Make the desire bend.
 After each bend is made, let spring to slid along the tubing to the next
section to be bent.

56
 Push the spring; do not pull, on the spring to remove it from the tubing.
 Pulling can permanently separate the spring coils, making the bender unfit for further use.
 Very little practice is needed to accomplish proper bends in smaller tubing with a spring
bender.
Procedure to Make Bends Using Bending Machine
 Always read the instructions for the bending machine before using it.
 Make sure that the correctly sized former and bending roller are fitted to the machine; one size
of former/roller will only bend one size of pipe.
 Place the pipe in the machine, remember that the pipe is secured at one end, so carefully
measure from the center of the former so that the bend is formed in the required position of
the pipe.
 Use the lever handle of the machine to apply roller pressure to the pipe and form the pipe
around the former.
 Move the lever smoothly until the required bend is achieved.

57
 The pipe will tend to spring back a certain amount when the pressure is released but be
carefully of over bending as this is not always easy to recover it.
 Release the pipe from the machine.
Swaging Techniques
Swaging involves enlarging the diameter of one end of a length of soft copper tubing so the end
of another length can be slipped into it. The connection is then soldered or brazed to make a
strong, leak proof joint. Swaging is the preferred method of joining soft tubing since the process
requires little time, and only one brazed joint is needed to complete the connection (compared
to two joints for a fitting).
Swaging method
Swaged connections can be made using either the punch-type joint method or the screw-type
joint method. Both punch- and screw-type joints require the use of special hand tools.
Procedure to Enlarge the Diameter Using Punch-type swage
 Clamp the tube into a special tool called a flaring block.
 Accomplish the enlarging process by pressing swaging tool.
 Ensure that the depth of the finished swage is equal to the original tubing diameter. For
example, 1/4″ tubing is swaged 1/4″ deep, and 1/2″ tubing is swaged 1/2″ deep.

58
 Swaging punches are available in diameters ranging from 3/16″ to 7/8″.
Making Flare Joint
Flaring copper tubing is a process of expanding or spreading the end of the tube into a funnel
shape with a 45° angle. All refrigeration flare fittings are made with a 45° angle so the tubing
will fit snugly against the fitting. A flare nut is used to compress the flare against the fitting to
obtain a tight, leak proof, metal-to-metal contact. Refrigeration tubing connections must
withstand at least 300 psi (pounds per square inch) of pressure without leaking. Because the
flare connection is a mechanical, metal-to-metal contact without gaskets, it is vital that proper
attention and care be given to making the flares.
Procedure to Enlarge the Diameter Using Punch-type swage
 First of all, ream the tubing end properly with help of file and sand.
Because burrs or rough edges will interfere with the smooth metal-to-metal
contact and permit leakage.

59
 Don’t forget to insert a flare nut before flaring the cooper tube.
 Clamp the tube in a flaring block with its end protruding slightly above the chamfer (beveled
edge) on the block’s top side.

60
 Now, a screw-type yoke with a special flaring adapter is then clamped onto the block and
automatically centered above the tube.
 Turning the screw will force the cone-shaped adapter into the tubing end, spreading it until it is
formed to a 45° angle against the chamfer.

61
 Connect to the fitting. Hold the flared end on the fitting and tighten the nut. Make it snug, but
don’t over-tighten.
Flare Defects
Extending the tubing too high above the chamfer will result in a flare that is too wide. This
prevents the nut from sliding over the flare. If the tubing is too low in the chamfer, the result is
a small flare that can pull free from the flare nut. A properly made flare will almost fill the
bottom of the flare nut without binding or rubbing the threads.

62
Making a Double Thickness Flare
A double thickness flare provides more strength at the flare end of tube. This is a two-step
operation. Either a punch or block or combination of flaring tool is used with Adapter. Adapter
tends to make double flare.
The Oxy-Acetylene Process
The oxyacetylene process produces a high temperature flame, over 3000 degrees C, by the
combustion of pure oxygen and acetylene.
Safe Storage

63
Safe practice and accident avoidance
 Store the cylinders in a well-ventilated area, preferably in the open air
 The storage area should be well away from sources of heat, sparks and fire risk
Safe practice and accident avoidance
 Cylinders are very heavy and must be securely fastened at all times
 Cylinder valves or valve guards should never be loosened
Backfire or flashback Procedure
After an un-sustained backfire in which the flame is extinguished:
 Close the blowpipe control valves (fuel gas first)
 Check the nozzle is tight
 Check the pressures on regulators
 Re-light the torch using the recommended procedure
If the flame continues to burn:
 Close the oxygen valve at the torch (to prevent internal burning)
 Close the acetylene valve at the torch
 close cylinder valves or gas supply point isolation valves for both oxygen and acetylene
 Open both torch valves to vent the pressure in the equipment
 Close torch valves
 Check nozzle tightness and pressures on regulators
 Re-light the torch using the recommended procedure
If a flashback occurs in the hose and equipment, or fire in the hose, regulator connections or
gas supply outlet points:
 Isolate oxygen and fuel gas supplies at the cylinder valves or gas supply outlet points (only if
this can be done safely)
 If no risk of personal injury, control fire using first aid fire-fighting equipment
 If the fire cannot be put out at once, call emergency fire services
 After the equipment has cooled, examine the equipment and replace defective components
Set up Oxy-Acetylene Welding Equipment for Soldering and Brazing Process
Step-by-Step Instructions:
1. Equipment assembly: Ensure that the equipment is assembled correctly as in figure.
2. Check equipment: First, make sure that the gas flow from both the oxygen and the acetylene
cylinders is turned off tightly. The two cylinders are secured in an upright position. This is
usually on a wheeled trolley. Look at the hose pressure and cylinder pressure gauges on top of
each cylinder. Both gauges on each cylinder should read zero. If both gauges do not read zero,
turn the main cylinder valve on the top of the cylinder clockwise, to close it completely. Then
you must purge the system of any gas.
3. Purge the system: To purge the system, make sure the main cylinder valve is closed tightly. Pick
up the torch handle and note that it has two hoses attached. One hose supplies acetylene, the

64
other oxygen. Turn the oxygen regulator under the gauges clockwise and open the oxygen valve
on the handle. This will purge any gas that may still be in the system and the gauges should
both drop back to zero. Repeat this procedure with the acetylene cylinder.
4. Install the torch handle: The torch handle is the connection between the hoses and the
working tips. It consists of a body and two taps. It’s used for both welding, Brazing and heating.
Different attachments are connected to the handle to enable cutting. Examine the connections.
One connection is marked “OX” and is for the oxygen hose. The other is marked “AC” and is for
the acetylene hose.
5. Connect the hoses: As a further safety precaution, you’ll find the
oxygen connector is right hand thread and the acetylene connector is
a left hand threads.
6. Install the correct tip: Welding tips come in sizes that are stamped with a number. Number one
is the smallest tip. The larger the number, the larger the tip and the greater the heat that it will
provide. Select the tip size suitable for the task and screw it onto the end of the torch handle.
Hold the torch handle in your hand, so that you can comfortably adjust the oxygen and
acetylene taps. Position the tip so that it faces away from you. Gently tighten the tip-securing
fitting.
7. Adjust the pressure of the gas flow: You are now ready to adjust the gas pressure for heating.
Look at the two valves on the torch handle. The valve next to the oxygen hose controls the flow
of oxygen to the tip. Close it tightly clockwise. The valve next to the acetylene hose controls the
flow of acetylene to the tip. Also, close it tightly clockwise.
8. Turn on the gases: Now that you’re ready to use the torch, turn the main valve on the top of
each cylinder counter-clockwise half a turn to open the valve. The needle on the cylinder
pressure gauge will rise to show you the pressure in the cylinder. Turn the oxygen regulator
handle clockwise until the needle in the gauge registers 2-5 PSI. Turn
the acetylene regulator handle clockwise until the needle in the gauge
registers 2-5 PSI. This is your working pressure for welding light plate.
9. Check the area: Before you light the torch, check the area you’re working in to make sure there
are no flammable materials or fluids nearby. Workmates should also be clear of the area. The
welding flame is not only extremely hot; it also produces dangerous ultra violet rays, which will
damage your eyes. It is absolutely vital that you are wearing the right safety gear: gloves and
tinted goggles or face mask. So, put them on and adjust them comfortably.
10. Ignite the torch: Now you are ready to ignite the torch with the striker. The tip of the torch
must be pointing downwards away from your body and away from the gas cylinders. Turn the
acetylene valve on the torch handle slightly towards the ‘ON’ position. You should hear the gas
hissing. Hold the striker against the tip of the torch with the lighter cup between the torch and
you. Flick the striker to create the spark that will ignite the gas at the tip of the torch. Open the

65
acetylene valve slowly until the sooty smoke produced by the torch disappears. Then slowly
open the oxygen valve on the torch handle.
11. Adjust the flame: As you open the oxygen valve, you will see the color of the flame change. The
pure acetylene flame is yellow, and it will change to blue as you add the oxygen. Continue to
open the oxygen valve until you can observe a small, sharp blue cone in the center of the torch
flame. This is the “neutral”, you can now adjust to the desired flame, for the task you are doing.
(Welding, brazing)

67
Soldering Techniques
 Cut it tight and square. Use a tubing cutter, rather than a hacksaw, to make a perfectly square
cut.
 Ream the end of the pipe to remove the burr left by the pipe cutter.
 Clean both surfaces until they shine like a brand-new.
 Now we need to a powerful safe torch, burn it up to blue flame not come. Direct the flame to
the middle of the fitting (The hottest part of the flame).
 Continue to apply heat until the flux begins to melt and the copper takes on a shiny. Then
touch the tip of the solder to the joint; if it’s hot enough, the solder will pour in and encircle the
fitting before it begins to overflow.

68
 Work from lowest to highest. Solder the low end of a fitting first because the high side will stay
hotter longer.
 Clean the joints after the cooling.

69
Difference between Brazing and Soldering Process
One of the main differences between brazing and soldering is working temperature. Soldering
takes place below 449 ° C (840 ° F) while the brazing above 644° C (1190° F). Apart from this the
all other techniques are same.
Brazing Techniques
 Mark the tube for the proper length with help of measuring tape.
 Cut the tube using a hacksaw or tube cutter.
 Ream the ends of the cut tube to remove any metal spurs by sand cloth or file.
 Insert the tube onto the fitting to ensure a snug fit, but that also
leaves enough room for the capillary action of the solder. Firmly support the tube.

70
 Hold the flame perpendicular to the tube and preheat both the tube and the fitting cup. Do not
overheat since this could cause the flux to burn. Preferably use an oxy fuel torch with a neutral
flame. Keep the flame in motion and to not linger on any one part of the tube.
 Touch the filler metal to the joint which should start to melt. Apply at the point where the tube
enters the socket of the fitting. When the filler metal melts, apply the heat source to the base
of the cup.
 Touch the filler metal to the joint which should start to melt. Apply at the point where the tube
enters the socket of the fitting. When the filler metal melts, apply the heat source to the base
of the cup.
 Leave the joints to cool without using water. After cooling clean the flux.
Purpose of Evacuation
When a typical system is installed and/or serviced, air and moisture enter the system. Oxygen,
nitrogen and moisture are all detrimental to system operation. Removal of the air and other

71
non-condensable is called “degassing,” and removal of the moisture is called “dehydration.”
Removal of both is typically referred to as evacuation. It causes –
 Pressure in the system rises
 Operating current rises
 Cooling (or heating) efficiency drops
 Moisture in the air may freeze and block capillary tubing
 Water may lead to corrosion of parts in the refrigerant system.
Theory Involved with Evacuation
A suitable vacuum pump, one capable of blank-off to at least 300 microns or lower, must be
connected to both the high and low sides of the refrigeration system. The size of the connecting
hoses should be such that they will not restrict the flow from the system to the vacuum pump.
A vacuum gauge that reads in microns should be connected to the furthest point in the system
away from the vacuum pump.
A triple evacuation process is strongly recommended. For triple evacuation, pump down the
refrigeration system to 1,500 microns, and then break the vacuum using dry nitrogen. At 1,500
microns any moisture or ice trapped in the system will outgas. After backfilling with dry
nitrogen to atmospheric pressure, operate the vacuum pump a second time to 1,500 microns
and again backfill with dry nitrogen. Finally, operate the vacuum pump the third time to 300
microns, but no lower. Close all valves and isolate the vacuum pump, then turn the vacuum
pump off.

72
Caution:
At a pressure below 300 microns (µT) the POE oil in the compressors will start to degrade and
begin losing its lubricating ability.
Watch the vacuum gauge to ensure vacuum is holding. If after five minutes there is a slight loss
of vacuum, there could possibly be some residual out gassing in the system. Below 1,500
microns any remaining moisture is present as ice which will sublime. In this case the vacuum
pump should be operated one more time to further dry the system. After a hold time of ten to
fifteen minutes at 300 microns the system is considered successfully evacuated.
An inability to pump down to 1,500 microns indicates a system leak or a pump problem. A loss
of vacuum to above 1,500 microns during the hold test indicates a system leak. System leaks
must be repaired before the refrigeration system can be safely operated. Any system leak
requires you go through the necessary steps to insure there has been no contamination of the
refrigerant.
Something to remember: After you have finished using the vacuum pump, a good procedure is
to change the oil. Any contamination in the refrigeration system is now in the vacuum pump oil.
If you do not change the oil and the vacuum pump sits idle for any period of time, the
contamination will start attacking its internal components.
Deep Vacuum (Evacuation of system)
Equipment, Tools and Supplies:
1. 4 port manifold gauge set
2. High Capacity dual stage Vacuum pump (4 cf. or greater)
3. 134A Charging Cylinder and Charging Hose
4. Refrigerant Charging Scale
5. Temporary access Valves
6. Brazing Equipment
7. Fire Extinguisher
8. PPE - Personal Protection Equipment - Approved Eye Protection
9. Tubing Cutters
10. 1/2” wrench, 7/16” wrench, Pliers, Triangle File and Assorted hand Tools
11. Extension Tube with Pin Valve (For insertion into process tube)
12. 90 Degree shut off valves
13. VOM /AMP Probe
14. Dye Drier
Phase 1: Evacuation of System
1. Unplug or disconnect power to refrigerator, this will lock both sides of the 3-way valve in the
open position in order to service sealed system.

73
2. Remove the machine compartment cover.
3. Connect high and low side manifold hoses to the drier and process tube (Service Line) shut
off valves.
4. Connect a hose from evacuation manifold gauge valve to the inlet of the vacuum pump.
5. (Charging Cylinder) Connect a hose from the charging cylinder to the Refrigerant port on the
manifold.
5a. (Electronic scale) Connect a hose from the shut off valve attached to the refrigerant cylinder
to the Refrigerant port on the manifold.
6. Close all valves.
7. Open vacuum pump vent and start the vacuum pump.
8. Open the inlet valve on the vacuum pump.
9. Open the VAC valve on the manifold.
10. Open the REF valve on the manifold.
11. Open the high side manifold valve.
12. Open the high side shut off valve.
13. Open the low side manifold valve.
14. Open the low side shut off valve – Close vacuum pump vent.

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15. Evacuate from both the high and low side of the system.
Note: If the evaporator is cold open the door and allow warming or using a heat gun to heat
the evaporator
16. Evacuate the system until the pressure drops to a minimum of 30 psig (760 mm Hg,
760,000m microns).
17. Close the VAC valve on the gauge manifold and shut off the vacuum pump.
18. The 30 psig (760 mm Hg, 760,000m microns) vacuum should remain constant – any
increase in pressure indicates moisture in the system or a system or equipment leak.
19. If the vacuum remains at a minimum of 30 microns for 5 minutes proceed to the charging
phase.
Measurement of Vacuum
Measuring vacuum, as with any kind of measuring, requires standard units of measure. Inches
or millimeters of mercury, torr, and micron are three units of measure typically associated with
the vacuum furnace industry. Other fields of vacuum use Pascal (Pa or kPa.)
Types of Vacuum Measuring Instruments
As it has become practical and desirable to create higher and higher vacuums, it has also
become necessary to assess the level of those vacuums accurately. Absolute pressure is
measured relative to perfect vacuum (0 psig) with zero as its zero point.
Gauge pressure is relative to ambient air pressure (14.5 psig), using atmospheric pressure as its
zero point (0 psig = 14.5 psig).
Many gauges are available to measure vacuum within a vacuum furnace chamber. These
gauges vary in design based on the particular range of vacuum they are analyzing.
Removal of Moisture from Systems by Vacuum Pump
The purpose of this specification is to improve the effectiveness of our procedures for removing
moisture from refrigerating systems at the commissioning stage on sites. It should be noted
that this is not a factory vessel dehydration standard where different and rigorous procedures
are required and where we apply heat to pressure vessels to remove water following
hydrostatic pressure tests.
1. For the evacuation of an industrial refrigerating system, a vacuum pump of reasonable size
will be required. This should have a swept volume in the range of at least 280 to 425 liters
/minute (10 to 15 cfm). The vacuum pump should be associated with a vacuum gauge capable
of reading down to at least 1 torr or 1,000 microns. It is desirable to have a vacuum gauge on
the vacuum pump side of the isolating valve to check pump performance and there must be
another vacuum gauge on the plant side of the isolating valve to check behavior of the vacuum
when the pump has been valved off from the system. It is very important to use good quality
vacuum gauges and that these gauges are carefully stored and looked after when not in use.
Gauges that have been subject to rough handling or that are in any way in doubt should be
replaced or recalibrated.
2. The vacuum pump must be in good condition and capable of pulling a vacuum of 1000
micron against a shut valve.
3. The correct grade of vacuum pump oil to suit the pump must be used and must be changed
at least after every 10 hours operation or when it becomes “milky” or emulsified due to

76
moisture. Always put new oil in the pump before starting to evacuate a system. Wherever
possible we should avoid pumping refrigerant through the vacuum pump because the
refrigerant will contaminate the oil and rot the pump valves.
4. The vacuum pump must be connected to both high and low sides of the system being
evacuated.
5. Solenoid valves in the system should be jacked open, have a magnetic coil valve lifter fitted
or their seats and armatures should be removed. Where check valves or thermostatic
expansion valves are likely to prevent or restrict a flow path to the pump, system connections
from either side of the valve will be required.
6. A good place to connect the vacuum pump is in place of a relief valve on either the high or
low side of the system. For this purpose, a ¾” male NPT to ¾” male flare fitting would be
appropriate. The connections to the vacuum pump must be a generous size, minimum ½”. 6mm
tube may be used to connect to the high and low sides of the system if it is a very small system
(say internal volume less than about 200 liters).
7. Before starting to pull a vacuum, the complete system should be subjected to a strength
pressure test and a tightness test using oxygen-free nitrogen from a cylinder with a reducing
valve. The pressure test should be at the pressure stated on the refrigerant circuit diagram
(Diagram of Connections or P & ID). The pressure test has the additional benefit of removing
scale or flux which might seal a leak under vacuum.
8. Blow off all the pressure.
9. Connect the vacuum pump and commence evacuation using the gas ballast if the pump has
this facility.
10. Evacuate until a steady condition of 8 torr (8,000 microns) or less is achieved. 11. Shut the
vacuum pump suction valve and observe the vacuum on the system side, using a good quality
vacuum gauge. Wait for 30 minutes. If the pressure rises by more than 2 torr then this is not
acceptable and it is likely that either there is moisture in the system or a leak or both. If the
pressure rise is due to moisture it will be slower than if there is a leak and will tend to level off
at about the values given in the table in 12 for a given temperature. If moisture is present stop
the pump and remove the vacuum gauge. Use OFN to raise the pressure to atmospheric and
leave the system to stand for at least 1 hour to allow the dry nitrogen to absorb moisture.
Change the vacuum pump oil and run the pump again with vacuum gauge fitted. The vacuum
pressure achieved should be lower than the first evacuation. This process will need to be
repeated until the level of vacuum achieved and held after stopping the pump is less than the
values in the table, 12 only then will all the moisture have been removed. The final maximum
vacuum required and to be held can then be attained.
12. Once all possibility of leakage has been eliminated the pump should be operated without
gas ballast and run until a vacuum of better than 2 torr (2,000 microns) or 2.66 mbar has been
achieved and maintained for several hours. Note, virtually all of the air in the system can be
removed in about 10 to 15 minutes. However, moisture takes much longer. It is very important
that a sufficient length of time is allowed. The length of time required to remove moisture
depends on the quality of the vacuum pump and the temperature of the system at the time of
the evacuation. The table below is a good guide but only if you are using a high-quality vacuum
pump with good oil. The “temperature” represents the coldest part of the system.

77
13. When it is clear that there is no moisture in the system, the vacuum pump should be
isolated and the vacuum should be broken with refrigerant vapor. Particular care is required
when charging CO2 to prevent dry ice forming.
14. If the vacuum pump has a gas ballast facility it is good practice to run it for some time after
dehydration is complete, with its suction valve shut and the gas ballast fully open. This tends to
remove contaminants from the oil. Vacuum pumps are only as good as the vacuum oil which
they contain. When moisture has been removed by use of a vacuum pump, some of the
moisture contaminates the oil and must be drained off or driven off to restore the effectiveness
of the pump. Remember, it takes time and heat to remove moisture by vacuum. The process
cannot be hurried. It is much easier in summer than it is in winter. Starting to charge a
refrigerating system which has moisture in it will waste a lot more time and money than waiting
for the vacuum pump to do its job properly.
Leak Detection while in Vacuum
There are two methods to detect the leak while a system is in Vacuum-
By Helium Gas
The System of smaller volume is evacuated directly by the leak detector. If the system is of large
volume, it is additionally evacuated by a separate vacuum pump.
(a) In the spray-probe mode, a gas gun (connected to a helium cylinder) is used to discretely
spray He gas on suspected leak sites of the system. Any leaks are evidenced when He gas
molecules flows through the leaks of the evacuated system and is detected by the leak
detector.
(b) The system is placed in a volume containing He gas, which flows through all leaks to the
interior of the TP, where it is detected.

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By Soap Froth (Bubble Soap) Method
Make soap froth by shampoo and apply on the suspected leak sites. If the forth is un-stable in
desired time then we can detect the leak.
General Evacuation Procedures
If the system is large enough or if you must evacuate moisture from several systems, you can
construct a cold trap to use in the field.
Cold Trap
In the evaporation process, the Cold Trap is the coldest spot in the evaporation system. Vapors
naturally migrate to the coldest spot, where they freeze and are trapped in the condenser.
Because of this natural migration of the vapors, Cold Traps can also increase evaporation rates
since vapors are collected as a frozen solid (and are therefore not condensed inside the vacuum
tubing, which would slow evaporation).

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Nitrogen Pressure Holding in System and Standing Pressure Test
Equipment, Tools and Supplies:
1. 2 port manifold gauge set
2. Brazing Equipment
3. Fire Extinguisher
4. PPE - Personal Protection Equipment - Approved Eye Protection
5. Tubing Cutters
6. 1/2” wrench, 7/16” wrench, Pliers, Triangle File and Assorted hand Tools
7. Extension Tube with Pin Valve (For insertion into process tube)
8. Nitrogen cylinder with Regulator and gauge assembly
Phase 2: Nitrogen Pressure Holding in System
1. Unplug or disconnect power to the machine.
3. Connect the pin valve at service line/charging line braze it safely.
4. Connect a hose from manifold gauge valve to the inlet of the service line.
5. (N2 Cylinder) Connect a hose from the N2 cylinder to the Refrigerant port on the manifold.
6. Open the N2 cylinder valve slightly.
7. Open the manifold gauge valve.
8. Let the N2 gas flow in the system.
9. Check the pressure hold in the system through manifold gauge and close the manifold gauge
valve when pressure reaches at 250 psig.
10. Close the valve on the manifold.
11. Close the valve on the N2 cylinder regulator.
12. WARNING – Never start the system when pressure is hold.
13. Now check the standing pressure in system through pressure gauge.
Phase 3: Leak Detection through Nitrogen Pressure Holding in System
1. Hold the N2 pressure as described above in system.
2. Check the pressure after 2 and 5 hours, weather it is decreased or not.
3. If the standing pressure is less than the previous pressure.
4. Make froth bubble by shampoo and apply at the suspected area.
6. If the bubbles are not stable as desired, point out the leak
7. Open the leak point and re-braze it after proper cleaning.

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Cleaning a Dirty System with Nitrogen Gas
1. Unplug or disconnect power to the machine.
3. Disconnect the system (Evaporator or Condenser) from compressor assembly
4. Connect the pin valve at one end of the system braze it safely.
4. Keep the system open at other end of the system
5. (N2 Cylinder) Connect a hose from the N2 cylinder to the first end pin valve.
6. Open the N2 cylinder valve slightly.
7. Let the N2 gas flow in the system.
9. Press the other end by thumb.
10. When un-bearable pressure appears on the other end, realize it (Process called “Flushing”).
11. Make flush unless or until fresh N2 gas doesn’t come out.

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Chapter: 5
Compressors and Motors
4 Basic Refrigeration Systems &
Practice
 Types and function,
 Operation of reciprocating compressors,
 Operation of rotary compressors,
 Centrifugal compressors,
 Screw compressors,
 Helical compressors
 Single acting compressors,
 Double acting compressors,
 Two-stage and multi stage compression
compressors,
 Hermetic compressors,
 Semi-hermetic compressors,
 Overhauling and servicing of reciprocating
compressors,
 Open drive Compressors
 belt driven compressors,
 direct driven compressors, reciprocating
compressor components:
 crankshaft,
 connecting rod,
 piston,
 valve plate,
 shaft seal,
 reciprocating compressor efficiency
 Types of electric motors
 Uses of electric motors parts of an electric
motor,
 Electric motors determining motor speed,
 Power supply for electric motors
A compressor is a mechanical device that increases the pressure of a gas by reducing its
volume. (The fluid here is generally air since liquids are theoretically incompressible).
 George Medhurst of England designed the first motorized air compressor in 1799 and used
it in mining.

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Type and Function of Compressors
Compressors are classified on the basis of Volumetric Compression method as followed-
1. Positive Displacement
 Rotary Compressors
1. Screw Compressor
2. Scroll Compressor
3. Lobe Compressor
4. Vane Compressor
 Reciprocating Compressors
1. Single Acting Compressor
2. Double Acting Compressor
3. Diaphragm Compressor
2. Dynamic Compressors
 Axial Compressor
 Centrifugal Compressor
1. Single Stage Compressor
2. Multi stage Compressor
Compressors are classified on the basis of Structure method as followed-
1. Open Type
 Single Stage
 Two Stages
2. Hermetic Type
 Semi-Hermetic Type
 Hermetic Type
1. Positive Displacement Compressors
Positive-displacement compressors operate by forcing a fixed volume of fluid from the inlet
pressure section the compressor into the discharge zone of the compressor.
Reciprocating Compressors
Reciprocating Compressors are one of the most widely used types of compressors for
refrigeration and air conditioning applications. The reciprocating compressors comprise of the
piston and the cylinder arrangement similar to the automotive engine. While the engine
generates power after consuming fuel, the reciprocating compressor consumes electricity to
compress the refrigerant. Inside the cylinder the piston performs reciprocating motion which
enables the compression of refrigerant inside it.
Principle of Working of the Reciprocating Compressors
Apart from the piston and the cylinder arrangement, the reciprocating compressor also
comprises of the crankshaft, connecting rod and other small connecting elements. The
crankshaft is connected to the electric motor directly by coupling or by belt and driven by the
pulley arrangement. The rotary motion of the crankshaft is converted into the reciprocating

83
motion of the piston inside the cylinder via the connecting rod. Let us see the various strokes of
the piston inside the cylinder (refer the figures below):
Working of Reciprocating Compressor
1) Piston at Top Dead Center (TDC) Position:
Let us suppose that initially the piston is at the top position inside the cylinder; this is called as
the top dead center (TDC) position of the piston. From the top dead center position the piston
starts moving towards the downward direction. At this instance the discharge valve is already
closed, while the suction valve opens due to suction pressure of the refrigerant from the
suction pipeline. The refrigerant from the suction pipeline is taken inside the cylinder of the
compressor via the suction valve. As the piston moves downwards, the amount of the
refrigerant taken inside the cylinder increases. When the piston reaches bottom most position
it is said to be in bottom dead center (BDC) position. At this position the maximum amount of
the refrigerant is sucked by the cylinder or compressor.
2) Piston at Bottom Dead Center (BDC) Position:
At the BDC position the maximum amount of the refrigerant has been taken inside the cylinder
from the suction line of the refrigeration or air conditioning system. The piston now starts
moving in the upward direction due to which the volume of the refrigerant inside the cylinder
starts reducing, that means the refrigerant starts getting compressed and its pressure starts
increasing. Due to high pressure of the refrigerant inside the cylinder, its suction valve closes.
Due to crankshaft motion the piston continues moving upwards and compressing the
refrigerant. The pressure of refrigerant goes on increasing as it gets more and more
compressed. At the end of the compression stroke the discharge valve opens and the
refrigerant is delivered to the discharge pipeline or tubing of the refrigeration or the air
conditioning system. Due to the rotary motion of the crankshaft the reciprocating motion of the
piston continues inside the cylinder and it finally reaches the TDC position, where the entire
compressed refrigerant inside the cylinder is delivered to the discharge line and the discharge
valve closes. From here on the piston starts moving again to the BDC position and the operation
of the compressor continues.
Reciprocating Compressor Components:
Crankshaft
Larger compressors, normally above 150 kW (200 hp), have forged steel crankshafts for
compressor less than or equal to 150kW machines ductile iron crankshaft. Crankshafts should
have removable balance weights to compensate for rotary unbalance as well as reciprocating
unbalance. The crankshaft should be dynamically balanced when above 800 rpm.
Connecting Rod
For reciprocating compressor of above 150 kW (200 hp), have forged steel connecting rod are
used and for compressor less than or equal to 150kW machines ductile iron material is used.
Like Crankshafts, the connecting rod should have drilled hole for oil passage. The connection

84
rod is used to connect the crankshaft and the crosshead. The connecting rod converts the
rotary motion into
reciprocating motion. The connecting rod bolts and nuts shall be securely locked with cotter
pins or wire after assembly.
Piston Rod
The piston rod is threaded to the piston and transmits the reciprocating motion from the
crosshead to the piston. The piston rod is normally constructed of alloy steel and must have a
hardened and polished surface particularly where it passes through the cylinder packing
(double-acting cylinders).
Piston
The piston is the heart of the reciprocating compressor. The piston translates the energy from
the crankcase to the gas in the cylinder. In order to avoid the leakage of compressed gas
between the piston and cylinder, the piston is equipped with a set of sliding seals called as
piston rings. Usually, the rings are made of a material, that having self-lubricating property to
reduce the slide friction force between the cylinder and the piston. Normally the piston is made
up of lesser weight materials such as aluminum and aluminum alloys; this is to reduce the
reciprocating compressor shaking forces and Rod load. In the case, piston diameter larger
piston diameter hollow pistons are also used to reduce the weight. For low speed compressors
(up to 330 rpm) and medium speed compressors (330-600 rpm), pistons are usually made of
CAST IRON.
Valve Plate
The plate valves, as shown in Figure, are similar to the concentric ring valve except that the
rings are joined into a single element. The advantage is that the valve has single element
making flow control.

85
Somewhat easier, Because of the single element, the number of edges available for impact is
reduced. The valve may be mechanically damped, as this design permits the use of damping
plates. It has the disadvantage that because of the geometry used; the stress is higher due to
the potential of higher stress concentrations. These valves are mostly used in the industrial
process compressor.
Shaft Seal
Rod packing is required to prevent the gas leakage along the piston rod where it passes through
the crank end cylinder closure.
If cooling packing is required, the stuffing box may be jacketed for liquid coolant.
The packing rings are the heart of rod packing assembly. The main packing rings types are-
 Radial Ring or Pressure Breaker Ring
 Tangent Ring
 Backup ring
Cylinder Block and Piston
In most compressors, the cylinder block is integrated with the crankcase and forms a single
casting. The crankcase and the cylinder block are usually made of high-grade cast iron. In
medium and large reciprocating compressors, pre-machined cylinder liners or sleeves are often
inserted in the crankcase, and they can be replaced when worn. It costs far less to replace
cylinder liners or sleeves than to replace the cylinder block.
Suction and Discharge Valves
The suction valve controls the vapor refrigerant entering the cylinder, and the discharge valve
controls the hot gas discharging from the cylinder. Suction and discharge valves are usually

86
made of high carbon-alloy steel or stainless steel. Spring-action ring valves are most extensively
used in medium and large compressors. Ring valves are usually heat- treated to the resilience of
spring steel and must be precisely ground to a perfectly flat surface. A defection of 0.001 in.
(0.025 mm) may cause leakage.
Oil Lubrication
Oil lubrication is necessary to form a fluid film separating the moving surfaces to protect them
from wear and corrosion. Oil is also used as a coolant to carry heat away and cools the
refrigerant. Oil provides an oil seal between the piston and cylinder and between the valve and
valve plates. In refrigeration systems, mineral and synthetic oils are used for lubrication.
Accessories:
Liquid Receiver
If not all the refrigerant in the system can be condensed and stored in the condenser during the
shutdown period, a high-pressure-side liquid receiver is needed to provide auxiliary refrigerant
storage space. There are two types of receivers: through-type and surge-type receivers. In a
through-type receiver, the liquid flows from the condenser to the receiver and the pressure in
the receiver is always lower than that at the condenser outlet. For a surge-type receiver, its
purpose is to allow liquid to flow directly to the expansion valve and remain sub cooled.
Operation of Rotary Compressors
These compressors use rotors in place of pistons, giving a pulsating free discharge air. These
rotors are power driven. They have the following advantages over reciprocating compressors:
1. They require a lower starting torque
2. They give a continuous, pulsation free discharge air
3. They generally provide higher output
4. They require smaller foundations, vibrate less, and have lesser parts, which means less failure
rate
Centrifugal Compressors
Centrifugal compressors use a rotating disk or impeller in a shaped housing to force the gas to
the rim of the impeller, increasing the velocity of the gas. A diffuser (divergent duct) section,
also called plenum, converts the velocity energy to pressure energy; hence we get air at high
pressure.
They are primarily used for continuous, stationary service in industries such as oil refineries,
chemical and petrochemical plants and natural gas processing plants. They are generally single
stage machines, but with multiple staging, they can achieve high output pressures (>69 M Pa).
The centrifugal air compressor is an oil free compressor by design. The oil lubricated running
gear is separated from the air by shaft seals and atmospheric vents. It’s a continuous output
machine.

87
Screw Compressor
It is also called helical screw compressor because of two helical rotors.
1. Rotary screw compressor use two meshed rotating positive-displacement helical screws to
force the air into a smaller space.
2. These are usually used for continuous operation in commercial and industrial applications
and may be either stationary or portable.
3. Because of simple design and few wearing parts, rotary screw air compressors are easy to
install, operate, and maintain.
Rotary screw compressors are commercially produced in Oil flooded and Oil free types:
Oil flooded compressors are nothing but oil cooled compressors; where oil seals the internal
clearances of the compressor. Though filters are needed to separate the oil from the discharge
air, cooling takes place right inside the compressor, and thus the working parts never
experience extreme operating temperatures leading to prolonged life.
The oil free screw air compressors use specially designed air ends to compress air, giving true
oil free air. They are water cooled or air cooled and provide the same flexibility as oil flooded
rotary compressor.

88
(Fig. Rotary screw compressor working)
Working principle-Air sucked in at one end and gets trapped between the rotors and get
pushed to other side of the rotors. The air is pushed by the rotors that are rotating in opposite
direction and compression is done when it gets trapped in clearance between the two rotors.
Then it pushed towards pressure side.
Rotary screw compressors are of two types oil-injected and oil-free.
Oil-injected is cheaper and most common than oil-free rotary screw compressors.
Advantages
1. It is less noisy
2. These are called the work-horses as they supply large amount of compressed air.
3. More energy efficient as compared to piston type compressors.
4. The air supply is continuous as compared to reciprocating type compressors. Relatively low-end
temperature of compressed refrigerant.
Disadvantages
1. Expensive than piston type compressor.
2. More complex design.
3. Maintenance is very important.
4. Minimum one day use is required in a weak to avoid rusting.
Scroll Compressor
It is one of the best compressor types in rotary compressors. The air is compressed using two
spiral elements. One element is stationary and the other one moves in small eccentric circles
inside the spiral. Air gets trapped inside the spiral way of that element and gets transported in
small air-pockets to the center of the spiral.

89
Simply air gets trapped at the outer edge and get compressed due to reduction of are as it
travels from outer edge to inner edge. It takes about 2 to 3 turns for the air to reach the
pressure output in the center.
(Fig. Scroll Rotary air compressor)
Advantages
1. It is very quiet.
2. This is very compact in size.
3. Simple design with not so many parts, oil free design and low maintenance.
Disadvantages
1. Output capacity is low.
2. Relatively expensive.
Helical Compressors
Helical Compressor or rotary-screw compressor is a type of gas compressor that uses a rotary-
type positive-displacement mechanism. They are commonly used to replace piston
compressors where large volumes of high-pressure air are needed, either for large industrial
applications. The gas compression process of a rotary screw is a continuous sweeping motion,
so there is very little pulsation or surging of flow, as occurs with piston compressors.
Single Acting Compressor
A Single Acting Reciprocating (piston) compressor consists of a single cylinder which only takes
in and discharges fluid at one end.

90
Double Acting Compressor
A Double acting unit also has only one cylinder but it is piped up to take in and discharge fluid at
both ends.
Single–Stage Reciprocating Compressor
Compression is done in single stage or by single cylinder only and it is used for generation of
low pressure air.
Double–Stage Reciprocating Compressor
It is a compressor that produces highly pressurized air and mostly it is used nowadays in heavy
duty mechanical devices.

91
Hermetic Compressor
The compressor and motor are connected and housed in same housing, which is hermetic
sealed by welding. Compared with the semi hermetic compressors the hermetic compressor
excels in air tightness. Comparatively small size reciprocating compressors and rotary
compressors are in most cases of the hermetic type. In case of compressor failure, it is
necessary to replace whole compressor.

92
Semi-Hermetic Compressor
The compressor and motor are connected and housed in same housing. The cover of each part
is tightened by bolt. No shaft seal required because no gas leakage.

93
Overhauling and servicing of reciprocating compressors:
Service Procedures
The service section covers replacement of valve plates and gaskets, service to the bearing head
assembly containing the oil pump, and a clean-up procedure to follow in case of motor burn
out. Most other internal service requires replacement of the compressor.
REMOVE, INSPECT AND REPLACE CYLINDER HEAD AND VALVE PLATE ASSEMBLY
To test for leaking discharge valves or blown cylinder head or valve plate gaskets:
1. Pump compressor down.
2. Observe suction and discharge pressure equalization. If valves are leaking or a gasket is
blown, the pressure will equalize rapidly. Maximum allowable discharge pressure drop is 3 psi
per minute after initial drop of 10 to 15 psi in first half minute. New reed valves may require 24
to 48-hour run-in time to seat completely. A compressor bank (head) with a blown gasket can
also usually be detected by touch since the head temperature will normally be much hotter
than a bank with good gaskets.
3. If there is an indication of loss of capacity and discharge valves are functioning properly,
remove valve plate assembly and inspect suction valves.

94
NOTE: This test procedure is not applicable to compressors equipped with pressure actuated
un-loader valves due to rapid pressure equalization rate. Inspect suction and discharge valves
by disassembling valve plate.
Direct Driven Compressor
Direct Driven type compressor have the motor directly attached to the pump unit and can be
both lubricated or oil free. These compressors are maintenance free and during failure of
compressor hole compressed need to change.
Open Drive or Belt Driven Compressor
Belt-drive compressors have a V-belt running from a smaller pulley wheel on the motor to a
larger pulley wheel on the pump. Therefore, the pump spins slower than the motor. This is the
traditional arrangement for a long-lasting capable compressor. An additional advantage is that
if anything were to go wrong you can replace the individual parts. Motors and pumps are
commercial items.
Reciprocating Compressor Efficiency
Performance Assessment
Over a period of time, both performance of compressors and compressed air systems reduces
drastically. This is mainly attributed to poor maintenance, wear & tear, etc.
These lead to additional compressor installations which further reduce the efficiency.
Therefore, a periodic performance assessment is essential to minimize the cost of compressed
air.
Performance terms & Definitions
Compression ratio (r): It’s the ratio of absolute discharge pressure at last stage, to the absolute
intake pressure.

95
Where, P1 = absolute intake pressure
P2 = absolute delivery pressure
Capacity: The capacity of a compressor is the full rated volume of flow of gas compressed and
delivered under standard conditions of total temperature, total pressure, and composition
prevailing at the compressor inlet.
Free Air Delivery (Qf): It’s the actual flow rate, rather than rated volume of flow. It’s called free
air delivery (FAD) because it means air flow rate at atmospheric conditions at any specific
location, and not standard conditions.
Compressor Load: The loads on any air compressor are system frictional resistance, piping
backpressure and the head the load imposes.
Input Power: It’s the shaft horsepower supplied to the compressor including mechanical and
electrical losses in the drive system. This is the power that determines the electric bill.
Isothermal Power: It’s the least power required to compress air assuming isothermal (constant
temperature) compression conditions.
Where, P1= Absolute inlet pressure (kg/cm2).
r = compression ratio
Qf = Free air delivered (m3/hr)
Isothermal Efficiency: It’s the percentage ratio of isothermal power to shaft power supplied.
Isothermal Efficiency = Isothermal Power x 100
Actual measured Input Power
Volumetric Efficiency: It’s the ratio of free air delivered to the compressor swept volume.
Where, Qf = Actual free air delivery of compressor
D = cylinder bore, meter
L = cylinder stroke, meter
S = compressor RPM x = 1
for single acting, and 2 for double acting cylinders
Compression ratio (r) = P2/P1
Isothermal Power (kW) = P1 X Qf X log (r)
36.7
Volumetric Efficiency = Qf / compressor displacement x 100
Compressor displacement = π/4 x D2 x L x N x X x N

96
n = number of cylinders
Specific Power Consumption: It’s defined as input power (kW) per unit volume flow rate
(m3/h).
ELECTRIC MOTOR
Electric motors can be powered by alternating current (AC) or direct current (DC). AC electric
motors use a secondary and primary winding (magnet), the primary is attached to AC grid
power (or directly to a generator) and is energized. The secondary receives energy from the
primary without directly touching it. This is done using the complex phenomena known
as induction.
Types of Electric Motor
Electric motors can be categorized on the basis of electric supply-
a) Direct Current (DC) Motor
These motors are quite expensive requiring a direct current source or a converting device to
convert normal alternating current into direct current. They are capable of operating with
adjustable speeds over a wide range and are perfectly suited for accurate and flexible speed
control. Therefore, their use is restricted to special applications where these requirements
compensate the much higher installation and maintenance costs.
b) Alternating Current (AC) Motor
These are the most frequently used motors because electrical power is normally supplied as
alternating current. The most common types are:
Synchronous Motors: Synchronous motors are three-phase AC motors which run at fixed
speed, without slip, and are generally applied for large outputs (due to their relatively high
costs in smaller frame sizes).
Induction Motor: These motors generally run at a constant speed which changes slightly
when mechanical loads are applied to the motor shaft. Due to its simplicity, robustness and low
cost, this type of motor is the most widely used and, in practical terms, is quite suitable for
almost all types of machines. Currently it is possible to control the speed of induction motors by
frequency inverters.
Uses of Electric Motor Parts
There are many kinds of electric motors but in general they have some similar parts. Each
motor has a stator, which may be a permanent magnet or wound insulted wires. The rotor sits
the middle (most of the time) and is subject to the magnetic field created by the stator. The
rotor rotates as its poles are attracted and repelled by the poles in the stator. The strength of
the motor (torque) is determined by voltage and the length of the wire in an electromagnet in
the stator.
Specific Power Consumption = Input Power kWh/m3
Qf

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