DPG POLYTECHNIC GURUGRAM(HR) E-Notes for HYDRAULICS AND PNEUMATICS (Mechanical department)

By:Chandra Kumar Diwakar

Title Index

S.No. Unit No Unit Name Page No.

1. 4. Hydraulic Machines 2-8

2. 6. Oil power Hydraulic and Pneumatic systems 9-17

2 | P a g e

4. Hydraulic Machines

4.1 Hydraulic Press : Principle, Construction, Working with Applications

Defination: Hydraulic press is a mechanical device which is based on the ‘Pascal’s law’

which states that equal intensity of pressure exerts on all the directions in a closed

system. It applicable here in such a way that if there is any pressure change at one point

in a closed system then same intensity of pressure will change at other point in the same

system.

Construction and working of Hydrualic Press:

In practical hydraulic press system, generally multiple rams are assembled together. The

number of rams used depends upon the working load. In hydraulic press multiple rams of

small sizes are preferred instead of a single large size ram to control the thrust forces

because it is easy to control the thrust forces on small size as compare to large size. In

press assembly one side/table is always fixed while the other is moving by the application

of ram force and in between fixed as free side pressing operation is take place. Ram is

operated by the hydraulic pressure of fluid. The high pressure liquid is supplied by using

pump and hydraulic accumulator. Hydraulic accumulator works as the junction between

the pump and the rams. Hydraulic accumulator stores the high pressure liquid when press

is at stationary position. Hydraulic press is used where high thrust is required for

operation.

3 | P a g e

Applications:

▪ The major application of the hydraulic press is in industry where big size metal

objects transform into thin sheets by the application of pressure force.

▪ Sheet metal operations such as drawing, deep drawing, punching and blanking etc

▪ In crushing of scraps and old vehicles.

▪ In Packaging industry.

4.2 Hydraulic Jack : Principle, Construction, Working with Applications

Defination: A jack is a mechanical device which uses a screw thread or a hydraulic cylinder

to lift heavy loads or apply great linear forces. The most common forms of jacks available

in the market are Scissor car jacks, House jacks, Hydraulic jacks, Pneumatic jacks and

Strand jacks that are extensively used in Construction, Industrial, Automobile and

Engineering segments.

Construction and working of Hydrualic jack:

It consist of two cylinders of different sizes which are connected together by a pipe and a

hydraulic fluid or oil. The hydraulic fluid is incompressible and using a pump plunger is

forced into the cylinder of the jack. Oil is used because of its stable and self lubricating

nature. When the plunger pulls back, oil is drawn out of the reservoir and it goes inside

the pump chamber. When the plunger moves forward, the oil is pushed back into the

cylinder. This oil movement builds up pressure in the cylinder. And it is this pressure

which leads to the working of the hydraulic jack. It also find usage in workshops and also

lift elevators in low and medium rise buildings.

These can be segmented into two types: Bottle Hydraulic Jack and Floor Hydraulic Jack.

Bottle are portable in design; in these the piston is in a vertical position and it supports a

bearing pad which touches the object being lifted. Bottle Hydraulic are most appropriate

for lifting vehicles (cars, trucks, SUVs, trailers), houses and other heavy objects. In a Floor

Jacks, the piston is in a horizontal piston and there is a long arm which provide the vertical

motion to a lifting pad. There are wheels and castors in floor jacks.

4 | P a g e

The working principle of all hydraulic jacks is common but these differ in their shapes and

sizes. Hydraulic jacks with varied sizes and specifications are used to lift different types of

heavy equipment and vehicles such as bulldozers, forklifts, elevators, trolleys & trailers

and excavators. These can also be found in household equipments as well like door

stoppers, cars, bikes etc. Hydraulic Jacks are high in demand across the globe owing to

their sturdy construction, reliable & hassle free operation, unparalleled performance,

user-friendly design and less maintenance.

4.3 Hydraulic Accumulator : Principle, Construction, Working with Applications

Defination: Hydraulic accumulator is a mechanical device used in hydraulic applications. It

works as an intermediate device between supply lines of hydraulic fluid from pump to

required machines like hydraulic lift, hydraulic press, hydraulic cranes etc.

Constructions and working:

A simple hydraulic accumulator consists of a cylinder with inlet and outlet ports for the

hydraulic fluid, inlet are attached with the pump where as outlet is connected with the

operational machine. Cylinder consists of a ram with reciprocating motion inside the

cylinder and having some weight on the top of the ram. The arrangement of the ram and

cylinder should be vertical in position.

5 | P a g e

Pump continuously supplies the hydraulic fluid to the operating machine through the

accumulator, when there is no requirement of the fluid the outlet becomes close. This

time continuous supply from the pump raises the ram/plunger in the upward position

gradually till the extreme end or until the outlet is open. This operation helps to store the

hydraulic energy inside the accumulator for a small period of time. As the operating

machine require pressurized fluid for the power stroke then the outlet port becomes

open and ram with weights on the top starts slides downward gradually which results

high pressurized liquid is delivered to the operating machine during its power stroke. This

6 | P a g e

whole operation repeated continuously and helps us to do difficult tasks with small

investment of energy in daily life.

4.4 Hydraulic Brake: Principle, Construction, Working with Applications

Defination: Hydraulic brake is a type of braking system which is widely used in the

automobiles with the application of the hydraulic fluid. The working principle of hydraulic

braking system is purely based upon Pascal’s law, which states that the intensity of

pressure exerted inside a closed system by the liquid is always equal in all the directions.

Constructions and working:

1. Master cylinder:

It is the main part is the whole assembly. It works as a hydraulic actuator which has a

piston-cylinder arrangement. It is responsible for the conversion of mechanical force into

the hydraulic force. As the brake pedal is pressed the fluid in the master cylinder

7 | P a g e

compressed and exerts pressure which is transmitted to Brake assembly through the

hydraulic lines.

2. Brake pedal and mechanical linkage:

Brake pedal works as the input to the master cylinder or we can say that whole assembly

will start working when the brake pedal is pressed. It is pressed manually when we have

to stop or slow down the running body. It is further attached with little mechanical

linkage such as spring which helps in retraction of the pedal further it connects to master

cylinder. After the execution of the brake pedal, the master cylinder comes into the

working.

3. Hydraulic/brake fluid reservoir:

It is kind of a small tank for the braking fluid. It is directly attached to the master cylinder.

For the proper operation of hydraulic braking. It is necessary to maintain the accurate

amount of braking fluid in the whole assembly. Sometimes due to small leakages the level

of fluid goes down into the master cylinder so to maintain the proper amount of brake

fluid in the working operation a reservoir is required. The braking fluid goes into the

master cylinder from the reservoir when it is required.

4. Hydraulic lines:

Hydraulic lines are the connections between the various components of the braking

system. Braking fluid travels through these lines from master cylinder to brake. These are

the small diameter pipes which replace the different types of mechanical linkage in case

of mechanical brakes.

5. Brake caliper (In case of disc brake):

Brake calipers are the parts of the braking system in case of disc brakes which execute the

brake. Inside the brake calipers pistons are mounted which is responsible for the braking.

The brake pads are also attached with the piston. Calipers are mounted on the periphery

of the disc. The disc brake is externally applied braking system. A disc is mounted in

between the calipers.

6. Drum cylinder (In drum brake system):

Drum cylinder is a kind of small cylinder which is used in the Drum brakes and situated

inside the brake drum and connected to both the brake shoes. A drum brake is internally

applied brakes.

8 | P a g e

Working:

The working of the hydraulic braking system is very simple. To execute the brake we have

two types of components one is disc brake and the other is a drum brake. The initial

working for both the types is same but the execution technique is different. The disc

brake is externally applied brake by means of the brake caliper and disc whereas drum

brakes are internally applied by means of brakes shoes and brake drum. The working of

both the types is as follow:

Disc brake:

Working of the hydraulic braking system having disc brake starts with the pressing of

brake pedal. Due to compressive action the fluid the brake fluid compressed into the

master cylinder by means of piston-cylinder arrangement. The compressed fluid creates

pressure in the hydraulic supply lines and then transfers whole pressure energy at the

brake caliper of the disc brake. A disc is mounted in between the calipers. Both the

calipers have piston arrangement and brake pads are mounted on the piston. As the

brake pedal is pressed then the movement in the pistons starts i.e. both the pistons start

moving towards the discs and at the end brake caliper compresses the disc and brake

executed then running parts stop.

Drum brake:

The initial working of the drum brake is the same as disc brake the difference is in the

execution of the brake. In case of drum brake; drum and drum cylinder is used at the

place of disc and caliper. As the brake pedal is pressed the high-pressure fluid goes in the

drum cylinder of drum brake by means of hydraulic lines. As the fluid reaches into the

drum cylinder it starts expands and presses the brake shoes and brake is applied. When

we release the brake pedal then spring between both the brake shoes is responsible for

the releasing of the brake. After the releasing the brake pedal fluid from the brake

cylinder return back and brake released.

9 | P a g e

6. Oil power Hydraulic and Pneumatic systems

6.1 Introduction:

In the industry we use three methods for transmitting power from one point to another.

Mechanical transmission is through shafts, gears, chains, belts, etc. Electrical transmission is

through wires, transformers, etc. Fluid power is through liquids or gas in a confined space. In this

chapter, we shall discuss a structure of hydraulic systems and pneumatic systems. We will also

discuss the advantages and disadvantages and compare hydraulic, pneumatic, electrical and

mechanical systems.

6.2Applications of fluid power:

Agriculture Tractors; farm equipment such as mowers, ploughs,

chemical and water sprayers, fertilizer spreaders,

harvesters

Automation Automated transfer lines, robotics

Automobiles Power steering, power brakes, suspension systems,

hydrostatic transmission

Aviation

Fluid power equipment such as landing wheels in

aircraft.

Helicopters, aircraft trolleys, aircraft test beds,

luggage

loading and unloading systems, ailerons, aircraft

servicing,

flight simulators

Construction For metering and mixing of concrete rudders,

10 | P a g e

excavators,

industry/equipment

lifts, bucket loaders, crawlers, post-hole diggers,

road

graders, road cleaners, road maintenance vehicles,

tippers

Defense Missile-launching systems, navigation controls

Entertainment

Amusement park entertainment rides such as roller

coasters

Fabrication industry Hand tools such as pneumatic drills, grinders, borers,

riveting machines, nut runners

Food and beverage

All types of food processing equipment, wrapping,

bottling,

Foundry Full and semi-automatic molding machines, tilting of

furnaces, die-casting machines

Glass industry Vacuum suction cups for handling

11 | P a g e

Hazardous gaseous areas Hydraulic fracturing technologies: It involves pumping

large volumes of water and sand into a well at high pressure

to fracture shale and other tight formations, allowing

hazardous oil and gas to flow into the well. However,

hydraulic fracturing has serious environmental and water

pollution related issues.

Instrumentation Used to create/operate complex instruments in space

rockets, gas turbines, nuclear power plants, industrial labs

Jigs and fixtures Work holding devices, clamps, stoppers, indexers

Machine tools Automated machine tools, numerically controlled(NC)

machine tools

Materials handling Jacks, hoists, cranes, forklifts, conveyor systems

Medical Medical equipment such as breathing assistors, heart assist

devices, cardiac compression machines, dental drives and

human patient simulator

Movies Special-effect equipment use fluid power; movies such as

Jurassic park, Jaws, Anaconda, Titanic

Mining Rock drills, excavating equipment, ore conveyors, loaders

Newspapers and periodicals Edge trimming, stapling, pressing, bundle wrapping

12 | P a g e

Oil industry Off-shore oil rigs

Paper and packaging Process control systems, special-purpose machines for

rolling and packing

Pharmaceuticals Process control systems such as bottle filling, tablet

placement, packaging

Plastic industry Automatic injection molding machines, raw material

feeding, jaw closing, movement of slides of blow molder

6.3 Basic components of hydraulic system:

Hydraulic systems are power-transmitting assemblies employing pressurized liquid as a

fluid for transmitting energy from an energy-generating source to an energy-using point

to accomplish useful work. Figure shows a simple circuit of a hydraulic system with

basic components.

Load Motor 1 – Off 2 – Forward 3– Return

Pressure Filter regulator

Pump

1 3 2

Direction control valve

Oil tank

13 | P a g e

Actuator

Functions of the components shown in Fig. are as follows:

1. The hydraulic actuator is a device used to convert the fluid power into

mechanical power to do useful work. The actuator may be of the linear

type (e.g., hydraulic cylinder) or rotary type(e.g., hydraulic motor) to

provide linear or rotary motion, respectively.

2. The hydraulic pump is used to force the fluid from the reservoir to rest of

the hydraulic circuit by converting mechanical energy into hydraulic

energy.

3. Valves are used to control the direction, pressure and flow rate of a fluid

flowing through the circuit.

The piping shown in Fig. is of closed-loop type with fluid transferred from the storage

tank to one side of the piston and returned back from the other side of the piston to the

tank. Fluid is drawn from the tank by a pump that produces fluid flow at the required

level of pressure. If the fluid pressure exceeds the required level, then the excess fluid

returns back to the reservoir and remains there until the pressure acquires the required

level.

Cylinder movement is controlled by a three-position change over a control valve.

1. When the piston of the valve is changed to upper position, the pipe pressure line is

connected to port A and thus the load is raised.

2. When the position of the valve is changed to lower position, the pipe pressure line is

connected to port B and thus the load is lowered.

3. When the valve is at center position, it locks the fluid into the cylinder(thereby

holding it in position) and dead-ends the fluid line (causing all the pump output fluid to

return to tank via the pressure relief).

14 | P a g e

In industry, a machine designer conveys the design of hydraulic systems using a circuit

diagram. Figure shows the components of the hydraulic system using symbols. The working

fluid, which is the hydraulic oil, is stored in a reservoir. When the electric motor is switched

ON, it runs a positive displacement pump that draws hydraulic oil through a filter and delivers

at high pressure. The pressurized oil passes through the regulating valve and does work on

actuator. Oil from the other end of the actuator goes back to the tank via return line. To and fro

motion of the cylinder is controlled using directional control valve.

Cylinder Extended

Retract

Motor Directional control valve

Pump

Pressure regulator

Filter

Breather

Reservoir

15 | P a g e

6.4 Basic Components of a Pneumatic System:

The functions of various components shown in Fig.are as follows:

1. The pneumatic actuator converts the fluid power into mechanical power to

perform useful work.

2. The compressor is used to compress the fresh air drawn from the atmosphere.

3. The storage reservoir is used to store a given volume of compressed air.

4. The valves are used to control the direction, flow rate and pressure of compressed

air.

5. External power supply (motor) is used to drive the compressor.

6. The piping system carries the pressurized air from one location to another.

Air is drawn from the atmosphere through an air filter and raised to required pressure by an air

compressor. As the pressure rises, the temperature also rises; hence, an air cooler is provided to

cool the air with some preliminary treatment to remove the moisture. The treated pressurized air

then needs to get stored to maintain the pressure. With the storage reservoir, a pressure switch is

fitted to start and stop the electric motor when pressure falls and reaches the required level

16 | P a g e

6.5 Comparison between Hydraulic and Pneumatic Systems:

Usually hydraulic and pneumatic systems and equipment do not compete. They are so dissimilar

that there are few problems in selecting any of them that cannot be readily resolved. Certainly,

availability is one of the important factors of selection but this may be outweighed by other

factors. In numerous instances, for example, air is preferred to meet certain unalterable

conditions, that is, in“hot spots” where there is an open furnace or other potential ignition hazard

or in operations where motion is required at extremely high speeds. It is often found more

efficient to use a combined circuit in which oil is used in one part and air in another on the same

machine or process. Table 1.2 shows a brief comparison of hydraulic and pneumatic systems.

Table :Comparison between a hydraulic and a pneumatic system</table>

S. No. Hydraulic System

Pneumatic

System

It employs a pressurized liquid It employs a compressed gas, usually

1.

air, as a fluid

as a fluid

2.

An oil hydraulic system operates at A pneumatic system usually operates

pressures up to 700 bar at 5–10 bar

3. Generally designed as closed system Usually designed as open system

4.

The system slows down when leakage Leakage does not

affect the system

occurs much

5. Valve operations are difficult Valve operations are easy

17 | P a g e

6. Heavier in weight Lighter in weight

Pumps are used to provide Compressors are used to provide

7. compressed

gases

pressurized liquids

8. The system is unsafe to fire hazards The system is free from fire hazards

9.

Automatic lubrication is provided Special arrangements for lubrication

are needed

18 | P a g e

Objective Type Questions

Fill in the Blanks

1. Fluid power is the technology that deals with the generation, and transmission of

forces and movement of mechanical elements or systems.

2. The main objective of fluid transport systems is to deliver a fluid from one location to

another, whereas fluid power systems are designed to perform .

3. There are three basic methods of transmitting power: Electrical, mechanical and .

4. Only are capable of providing constant force or torque regardless of speed

changes.

5. The weight-to-power ratio of a hydraulic system is comparatively than that of an

electromechanical system.

State True or False

1. Hydraulic lines can burst and pose serious problems.

2. Power losses and leakages are less in pneumatic systems.

3. Pneumatic system is not free from fire hazards.

4. Hydraulic power is especially useful when performing heavy work.

5. Water is a good functional hydraulic fluid.

Review Questions:

1. Define the term fluid power.

2. Differentiate between fluid transport and fluid power systems.

3. Differentiate between hydraulics and pneumatics.

4. List the six basic components used in a hydraulic system.

5. List the six basic components used in a pneumatic system.

6. List 10 applications of fluid power in the automotive industry.

19 | P a g e

7. Name 10 hydraulic applications and 10 pneumatic applications.

8. List five advantages and five disadvantages of hydraulics.

9. List five advantages and five disadvantages of pneumatics.

10. List the main components of a fluid power system and their functions.

11. Discuss in detail the future of fluid power industry in India.

12. Compare different power systems used in industries.

13. What is the main difference between an open-loop and a closed-loop fluid power system?

14. List five major manufactures of fluid power equipment and systems in India.

15. List five major manufactures of fluid power equipment and systems in the world.

16. Visit any industry nearby and list the hydraulic/pneumatic parts or systems used and their purposes.

17. Why is the hydraulic power especially useful when performing heavy work?

18. Differentiate between oil hydraulics and pneumatics.

19. List any five applications of fluid power systems.

20 List the main components of a fluid power system and their functions.

Answers

Fill in the Blanks

1. Control

2. Work

3. Fluid power

4. Fluid power systems

5. Less

State True or False

1. True

2. True

3. False

4. True

5. False