Hydraulics & pneumatics (AU) unit-I

By,
Arulprakasam G
Assistant Professor
Dept.of.Mech.Engg.,
KIT-CBE.
HYDRAULICS AND PNEUMATICS

OBJECTIVES: L T P C
3 0 0 3
 To provide student with knowledge on the application of fluid power in process,
construction and manufacturing industries.
 To provide students with an understanding of the fluids and components utilized in
modern industrial fluid power system.
 To develop a measurable degree of competence in the design, construction and
operation of fluid power circuits.

UNIT - I
FLUID POWER PRINICIPLES AND HYDRAULIC PUMPS
Introduction to Fluid power – Advantages and Applications – Fluid power systems –
Types of fluids - Properties of fluids and selection – Basics of Hydraulics – Pascal’s Law
– Principles of flow - Friction loss – Work, Power and Torque Problems, Sources of
Hydraulic power : Pumping Theory – Pump Classification – Construction, Working,
Design, Advantages, Disadvantages, Performance, Selection criteria of Linear and Rotary
– Fixed and Variable displacement pumps – Problems.

UNIT II
HYDRAULIC ACTUATORS AND CONTROL COMPONENTS
Hydraulic Actuators: Cylinders – Types and construction, Application, Hydraulic
cushioning – Hydraulic motors - Control Components : Direction Control, Flow control
and pressure control valves – Types, Construction and Operation – Servo and Proportional
valves – Applications – Accessories : Reservoirs, Pressure Switches – Applications –
Fluid Power ANSI Symbols – Problems.

UNIT III
HYDRAULIC CIRCUITS AND SYSTEMS
Accumulators, Intensifiers, Industrial hydraulic circuits – Regenerative, Pump Unloading, Double-
Pump, Pressure Intensifier, Air-over oil, Sequence, Reciprocation, Synchronization, Fail-Safe, Speed
Control, Hydrostatic transmission, Electro hydraulic circuits, Mechanical hydraulic servo systems.

UNIT IV
PNEUMATIC AND ELECTRO PNEUMATIC SYSTEMS
Properties of air – Perfect Gas Laws – Compressor – Filters, Regulator, Lubricator, Muffler, Air
control Valves, Quick Exhaust Valves, Pneumatic actuators, Design of Pneumatic circuit – Cascade
method – Electro Pneumatic System – Elements – Ladder diagram – Problems, Introduction to
fluidics and pneumatic logic circuits.

UNIT V
TROUBLE SHOOTING AND APPLICATIONS
Installation, Selection, Maintenance, Trouble Shooting and Remedies in Hydraulic and Pneumatic
systems, Design of hydraulic circuits for Drilling, Planning, Shaping, Surface grinding, Press and
Forklift applications. Design of Pneumatic circuits for Pick and Place applications and tool handling
in CNC Machine tools – Low cost Automation – Hydraulic and Pneumatic power packs.

UNIT - I
FLUID POWER PRINICIPLES AND HYDRAULIC PUMPS

INTRODUCTION TO FLUID POWER
 Fluid power technology actually began in 1650 with the discovery of Pascal's law.
 Pascal found that when he rammed a cork down into a jug completely full of
wine, the bottom of the jug broke and fell out.
 He found “Pressure applied to a confined fluid is transmitted undiminished in all
directions throughout the fluid and acts perpendicular to the surfaces in contact with
the fluid”.
 Pascal's law explains why a glass bottle, filled with a liquid, can break if a stopper
is forced into its open end.
 Pascal's law indicated that the pressures were equal at the top and bottom of the
jug. However, the jug has a small opening area at the top and a large area at the
bottom. Thus, the bottom absorbs a greater force due to its larger area.

INTRODUCTION TO FLUID POWER (Cont…)
Fig : Pascal’s Law
 The modern era of fluid power is considered to have begun in 1906 when a
hydraulic system was developed to replace electrical systems for elevating and
controlling guns on the battleship USS Virginia.
 For this application, the hydraulic system developed used oil instead of water.
This change in hydraulic fluid and the subsequent solution of sealing problems were
significant milestones in the rebirth of fluid power.

 Fluid power is the technology that deals with the generation, control, and
transmission of power, using pressurized fluids.
 Fluid power is used to push, pull, regulate, or drive virtually all the machines of
modern industry.
For example, fluid power steers and brakes automobiles, launches spacecraft,
moves earth, harvests crops, mines coal, drives machine tools, controls airplanes,
processes food, and even drills teeth.
 In fact, it is almost impossible to find a manufactured product that hasn't been
"fluid-powered" in some way at some stage of its production or distribution.

 Fluid power is called hydraulics when the fluid is a liquid and is called
pneumatics when the fluid is a gas.
 Thus fluid power is the general term used for both hydraulics and pneumatics.
 Hydraulic systems use liquids such as petroleum oils, synthetic oils, and water.
The first hydraulic fluid to be used was water because it is readily available.
 However, water has many deficiencies. It freezes readily, is a relatively poor
lubricant, and tends to rust metal components.
 Hydraulic oils are far superior and hence are widely used in lieu of water.
 Pneumatic systems use air as the gas medium because air is very abundant and
can be readily exhausted into the atmosphere after completing its assigned task.
 Pneumatics systems exhibit spongy characteristics due to the compressibility of
air.

 There are actually two different types of fluid systems.
a) Fluid transport and
b) Fluid power.
FLUID TRANSPORT
The delivery of a fluid from one location to another to accomplish some useful
purpose.
Examples include
Pumping stations for pumping water to homes and
Cross-country gas lines etc.,

FLUID POWER
Fluid power systems are designed specifically to perform work.
The work is accomplished by a pressurized fluid bearing directly on an operating
fluid cylinder or fluid motor.
A fluid cylinder produces a force resulting in linear motion.
A fluid motor produces a torque resulting in rotary motion.
Thus in a fluid power system, cylinders and motors (which are also called
actuators), provide the muscle to do the desired work. Of course, control components
such as valves are needed to ensure that the work is done smoothly, accurately,
efficiently, and safely.

ADVANTAGES (LIQUIDS):
 Ease and accuracy of control
 Multiplication of force
 Constant force or torque
 Simplicity, safety, economy
ADVANTAGES (GASES):
 It is fire resistant
 It is not messy
 It can be exhausted back into the atmosphere

DISADVANTAGES (LIQUIDS):
 Hydraulic oils are messy, and get leak
 Hydraulic lines can burst possibly
 Oils can cause fires
DISADVANTAGES (GASES):
 Due to its compressibility, cannot be used in an application where accurate
positioning or rigid holding is required
 Air can be corrosive, since it contains oxygen and water
 A lubricant must be added to air to lubricate valves and actuators
 Loud noise

APPLICATIONS :
Fluid power drives,
 Tankers and harvesting equipments
 Excavators
 Robotic dexterous arm
 Loads (Punching, pressing etc.,)

HYDRAULIC FLUID :
A hydraulic fluid has the following four primary functions
 Transmit power
 Lubricate moving parts
 Seal clearances between mating parts
 Dissipate heat

HYDRAULIC FLUID :
Primary properties
 Density
 Viscosity
1. Dynamic viscosity or absolute viscosity (μ)
Viscosity measured under force induced flow that is force per unit area (shear
stress) required to move one surface over another in a second is called dynamic
viscosity.
2. Kinematic viscosity (ν)
Viscosity measured under gravity induced is called kinematic viscosity. It is the
ratio of dynamic viscosity and density.
 Viscosity Index (VI)
 Bulk modulus (β)

HYDRAULIC FLUID :
To accomplish properly the four primary functions and be practical from a safety and
cost point of view, a hydraulic fluid should have the following properties:
 Good lubricity
 Ideal viscosity
 Chemical stability
 Compatibility with system materials
 High degree of incompressibility
 Fire resistance
 Good heat-transfer capability
 Low density
 Foam resistance
 Non toxicity
 Low volatility

TYPES OF HYDRAULIC FLUIDS :
 Water based (Water and water solutions)
 Oil based (Petroleum based oils and synthetic oils)
Bulk modulus (β)

CIRCUIT DIAGRAM

EXTERNAL GEAR PUMP :
modulus (β)

 Which develops flow by carrying fluid between the teeth of two meshing gears.
 One of the gears is connected to a drive shaft connected to the prime mover. The
second gear is driven as it meshes with the driver gear.
 Oil chambers are formed between the gear teeth.
 The suction side is where teeth come out of mesh, and it is here that the volume
expands, bringing about a reduction in pressure to below atmospheric pressure.
 Fluid is pushed into this void by atmospheric pressure because the oil supply tank
is vented to the atmosphere.
 The discharge side is where teeth go into mesh, and it is here that the volume
decreases between mating teeth. Since the pump has a positive internal seal against
leakage.
 The oil is positively ejected into the outlet port.

 The following analysis permits us to evaluate the theoretical flow-rate of a gear
pump using specified nomenclature:
Do =outside diameter of gear teeth (in, m)
Di = inside diameter of gear teeth (in, m)
L = width of gear teeth (in, m)
Vp = displacement volume of pump (in/rev, m/rev)
N = rpm of pump
QT = theoretical pump flow-rate
Then the volumetric displacement can be represented by,

ADVANTAGES :
 High volumetric efficiency
 Self priming
 Compact in size
 Can handle high viscous fluids
DISADVANTAGES :
 Unbalanced forces on the shaft
 Flow rate can not be varied
 Need strainer on the suction side
 Little noisy operation

INTERNAL GEAR PUMP :
modulus (β)

 It is the general family of gear pumps.
 The design consists of an internal gear, a regular spur gear, a crescent-shaped seal,
and an external housing.
 As power is applied to either gear, the motion of the gears draws fluid from the
reservoir and forces it around both sides of the crescent seal.
 Crescent seal acts as a seal between the suction and discharge ports.
 When the teeth mesh on the side opposite to the crescent seal, the fluid is forced
to enter the discharge port of the pump.

ADVANTAGES :
 Pulse free operation
 Self priming
 Compact in size
 Operates well in either direction
DISADVANTAGES :
 Limited pressure only can be handled
 Operation at moderate speed only

GEROTOR PUMP :
modulus (β)

GEROTOR PUMP :
 The Gerotor pump, operates very much like the internal gear pump.
 The inner gear rotor (Gerotor element) is power-driven and draws the outer gear
rotor around as they mesh together.
 This forms inlet and discharge pumping chambers between the rotor lobes.
 The tips of the inner and outer rotors make contact to seal the pumping chambers
from each other.
 The inner gear has one tooth less than the outer gear.
 The volumetric displacement is determined by the space formed by the extra tooth
in the outer rotor.

GEROTOR PUMP :
ADVANTAGES :
 High speed operation
 Self priming
 Quieter in operation
DISADVANTAGES :

LOBE PUMP :
modulus (β)

GEROTOR PUMP :
 It operates in a fashion similar to the external gear pump.
 Unlike the external gear pump, both lobes are driven externally so that they do not
actually contact each other.
 Thus, they are quieter than other types of gear pumps.
 Due to the smaller number of mating elements, the lobe pump output will have a
somewhat greater amount of pulsation.
 Its volumetric displacement is generally greater than that for other types of gear
pumps.

LOBE PUMP :
ADVANTAGES :
 High volumetric displacement when compared with other gear pumps
 Self priming
 Lobes have no direct contact
DISADVANTAGES :
 High pulsation

SCREW PUMP :
modulus (β)

SCREW PUMP :
 It is an axial flow positive displacement pump.
 Three precision ground screws, meshing within a close-fitting housing, deliver
nonpulsating flow quietly and efficiently.
 The two symmetrically opposed idler rotors act as rotating seals, confining the
fluid in a successcion of closures or stages.
 The idler rotors are in rolling contact with the central power rotor and are free to
float in their respective housing bores on a hydrodynamic oil film.
 There are no radial bending loads. Axial hydraulic forces on the rotor set are
balanced, eliminating any need for thrust bearings.

SCREW PUMP :
ADVANTAGES :
 High speed operation
 Self priming
 High suction head
DISADVANTAGES :
 High cost (because of high tolerances)
 Limited to viscosity range

VANE PUMP :
modulus (β)

VANE PUMP (Unbalanced):
 The rotor, which contains radial slots, is splined to the drive shaft and rotates
inside a cam ring.
 Each slot contains a vane designed to mate with the surface of the cam ring as the
rotor turns.
 Centrifugal force keeps the vanes out against the surface of the cam ring.
 During one-half revolution of rotor rotation, the volume increases between the
rotor and cam ring.
 The resulting volume expansion causes a reduction of pressure. This is the suction
process, which causes fluid to flow through the inlet port and fill the void.
 As the rotor rotates through the second half revolution, the surface of the cam ring
pushes the vanes back into their slots, and the trapped volume is reduced.
 This positively ejects the trapped fluid through the discharge port.

ADVANTAGES :
 Self priming
 Less leakages
DISADVANTAGES :
 Not suitable for high pressure
 Limited to viscosity range

VANE PUMP (Balanced) :
modulus (β)

 It has two intake and two outlet ports diametrically opposite each other.
 Pressure ports are opposite each other, and a complete hydraulic balance is
achieved.
 Instead of having a circular cam ring, a balanced design vane pump has an
elliptical housing, which forms two separate pumping chambers on opposite sides of
the rotor.
 This eliminates the bearing side loads and thus permits higher operating
pressures.
 A balanced vane pump containing vanes and a spring-loaded end plate.
 The inlet port is in the body, and the outlet port is in the cover, which may be
assembled in any of four positions for convenience in piping.
 One disadvantage of a balanced vane pump is that it cannot be designed as a
variable displacement unit because of elliptical housing.

VANE PUMP (Balanced):
ADVANTAGES :
 Self priming
 Less leakages
DISADVANTAGES :
 Not suitable for high pressure applications
 Not suitable for high viscosity fluids

PISTON PUMP (Bend Axis) :
modulus (β)

PISTON PUMP (Swash Plate Type) :
modulus (β)

PISTON PUMP (Radial Type) :
modulus (β)

PUMP SELECTION :
 Select the actuator (hydraulic cylinder or motor) that is appropriate based on the
loads encountered.
 Determine the flow-rate requirements. This involves the calculation of the flow
rate necessary to drive the actuator to move the load through a specified distance
within a given time limit.
 Select the system pressure. This ties in with the actuator size and the magnitude of
the resistive force produced by the external load on the system. Also involved here is
the total amount of power to be delivered by the pump.
 Determine the pump speed and select the prime mover. This, together with the
flow-rate calculation determines the pump size (volumetric displacement)
 Select the pump type based on the application (gear. vane, or piston pump and
fixed or variable displacement).

PUMP SELECTION :
 Select the reservoir and associated plumbing, including piping, valving, strainers,
and other miscellaneous components such as accumulators.
 Consider factors such as noise levels, horsepower loss, need for a heat exchanger
due to generated heat, pump wear, and scheduled maintenance service to provide a
desired life of the total system.
 Calculate the overall cost of the system.

PUMP PERFORMANCE:

Hydraulics & pneumatics (AU) unit-I

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