ME3492 HYDRAULICS AND PNEUMATICS

1. Unit 1 - Fluid Power Principles and
Hydraulic Pumps

2. 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.

3. All machines require some type of power source and a way of
transmitting this power to the point of operation.
The three methods of transmitting power are:
 Mechanical
 Electrical
 Fluid
In this course we are going to deal with the third type of power
transmission which is the Fluid Power.

4.  Fluid power is the method of using pressurized fluid to transmit
energy.
 Fluid power is the technology that deals with the generation,
control, and transmission of power, using pressurized fluids.
 Liquid or Gas is referred to as a fluid. Accordingly, there are
two branches of fluid power; Pneumatics, and Hydraulics.

5.  Ancient historical accounts show that water was
used for centuries to produce power by means of
water wheels, and air was used to turn windmills
and propel ships.
 Pascal’s law [1647–48] and Bernoulli’s law [1738]
operate at the very heart of all fluid power.
 In 1906 when a hydraulic system was developed to
replace electrical systems for elevating and
controlling guns on the battleship USS Virginia.
 In 1926 the United States developed the first
unitized, packaged hydraulic system consisting of a
pump, controls, and actuator.

6.  Fluid transport systems
Fluid transport systems have as their sole objective the
delivery of a fluid from one location to another to accomplish
some useful purpose
Example: pumping stations for pumping water to
homes.
 Fluid power systems
Fluid power systems are designed specifically to perform
work.
Example: Operating fluid cylinder or fluid motor.

7.  Hydraulic systems. (High Power Applications)
 Water Based (Water and Water Solutions)
 Oil Based (Petroleum oils and synthetic oils)
 Pneumatic Systems. (Low Power Applications)
 Air as the Gas medium.

8.  What is Hydraulic (from the Greek words hydra for water and
aulos for a pipe)?
Hydraulics is the discipline that deals with the mechanical
properties of liquids, and applies the principles to solve
engineering problems.
 Hydraulic systems are commonly used where mechanisms
require large forces and precise control.
 Examples include vehicle power steering and brakes, hydraulic
jacks and heavy earth moving machines.

10.  What is Pneumatic (from the Greek pneumn for wind or
breath).?
Pneumatics is the discipline that deals with mechanical
properties of gases such as pressure and density, and applies the
principles to use compressed gas as a source of power to solve
Engineering problems.

12. Mobile: Here fluid power is used to transport, excavate and lift
materials as well as control or power mobile equipment. End use
industries include construction, agriculture, marine and the military.
Applications include backhoes, graders, tractors, truck brakes and
suspensions, spreaders and highway maintenance vehicles.
Industrial: Here fluid power is used to provide power transmission and
motion control for the machines of industry. End use industries range
from plastics working to paper production. Applications include
metalworking equipment, controllers, automated manipulators,
material handling and assembly equipment.
Aerospace: Fluid power is used for both commercial and military
aircraft, spacecraft and related support equipment. Applications
include landing gear, brakes, flight controls, motor controls and cargo
loading equipment.

13.  Fluid power systems provide many benefits to users including:
 Multiplication and variation of force
 Easy, accurate control
 Multi-function control
 High horsepower, low weight ratio
 Low speed torque
 Constant force or torque-This is a unique fluid power attribute.
 Safety in hazardous environments

14.  A hydraulic element needs to be machined to a high degree of
precision.
 Leakage of hydraulic oil poses a problem to hydraulic
operators.
 Special treatment is needed to protect them from rust,
corrosion, dirt etc.,
 Hydraulic oil may pose problems if it disintegrates due to
aging and chemical deterioration.
 Hydraulic oils are messy and almost highly flammable.
 Hydraulic systems contain highly pressurized fluid. This can
cause burns, bruises or the accidental injection of fluid into the
body.

15.  Viscosity:
It is a measured of the sluggishness with which a fluid moves. When the viscosity is
low, the fluid flows easily because it is thin and has low body.
 Viscosity Index:
A low V.I. signifies a relatively large change of viscosity with changes
of temperature. In other words, the oil becomes extremely thin at high temperatures and
extremely thick at low temperatures. On the other hand, a high
V.I. signifies relatively little change in viscosity over a wide temperature range.

16. Other important Properties
1. Oxidation. 2. Flash point.
3. Fire point. 4. Corrosion.
5. Demulsibility. 6. Flammability.

17.  Energy:
The ability to do work
 Energy Transfer:
From prime mover, or input source, to an actuator, or output device

18.  Work:
Force multiplied by distance - Measured in foot-pounds.
 Power:
The rate of doing work.
Work over time in seconds.
 Torque:
Twisting force x distance - Measured in foot-pounds.

19. Positive
displacement
pumps
Gear pumps Vane pumps Piston pumps

20. Vane pumps
Fixed Displacement
Vane pump
Variable Displacement Vane
pump
Balanced Vane
pump
Unbalanced
Vane pump

21. Type of
Pump
Pressure
Rating (bar)
Speed Rating
(rpm)
Overall
Efficiency
(%)
HP per
Ib Ratio
Flow in
Ipm
External gear
pump
130-200 1200-2500 80-90 2 5-550
Internal gear
pump
35-135 1200-2500 70-85 2 5-750
Vane pump 70-135 1200-1800 80-95 2 5-300
Axial piston
pump
135-800 1200-1800 90-98 4 5-750
Radial piston
pump
200-800 1200-3000 85-95 3 5-750

22.  A slotted rotor is eccentrically supported in a cycloidal cam.
 The rotor is located close to the wall of the cam so a crescent-
shaped cavity is formed.

24.  1- Handles thin liquids at relatively higher pressures
 2- Compensates for wear through vane extension
 3- Can run dry for short periods
 4- Can have one seal or stuffing box
 5- Develops good vacuum

25.  balanced vane pump is one that has two intake and two outlet ports
diametrically opposite each other.

26.  In variable displacement the discharge of pump can be changed by
varying the eccentricity between rotor and pump cam-ring.

28.  low noise but higher than screw pump.
 Range of work from 500 – 1800 r.p.m
 Semi continuous flow
 Pressure of work between 50 – 80 bar
 Vane motor must have spring backward to the vane to face the flow.

29.  Q = (No. of Pistons) x (Piston Size) x (Piston Stroke) x (Drive Speed)

30.  Presence of foreign particles
 Foams and bubbles
 Overheating of oil
 Wrong selection of oil.

31.  Flow rate requirement
 Operating speed
 Pressure rating
 Performance
 Reliability
 Maintenance
 Cost and Noise
 Fluid Type

33.  Volumetric Efficiency
 Mechanical Efficiency
 Overall Efficiency
ηmech =Tth /TA