Hydraulic and Pneumatic Question Paper
Hydraulic and Pneumatic Question Paper
Hydraulic and Pneumatic Question Paper
This article is about (Hydraulics and Pneumatics Question paper) based on the
hydraulic and pneumatic subject this contains model questions and answers from
previous exams, This article is just to prepare for the exams.
Hydraulics means fluid form and the fluid can be defined as a substance that can flow
and does not maintain a fixed shape. Fluids display properties such as
Pneumatics means gas or air. It can be defined as a branch of fluids power in which gas
is used as a fluid.
Answer:
Methods of power transmission: There are basically 3 of transmission of power & they
are :
(a) Mechanical & Electrical mode: The power that drives a machine is transmitted
through.
(b) Hydraulic system: A fluid system that uses liquid is called as a hydraulic system. It
generates forces & transmits motion using hydraulic fluids.
(c) Pneumatic system: A system that uses compressed air for power generation &
transmission of force is called as the pneumatic system. Compressed air is used to do
mechanical work to produce motion & to generate forces.
2. Define pump and state the purpose of the pump in hydraulic system &
classify pumps.
Answer:
Definition of pump: The pump is a device that is used to pump fluid. A pump
converts mechanical energy into hydraulic energy.
Classification of Pumps.
Ans: External gear pump. In this type, gears are meshing with each other
one if the gear is connected to a drive shaft which is attached to the power
source.
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Hydraulic and Pneumatic Question Paper
4. How are the control valve classified? write the classification of the
control valve.
Answer:
The control valve is classified into 3 types depending upon the function they perform:
1. Directional control valves: Identify the path through which fluid passes in a
given circuit.
2. Pressure control valve: It protects the system against the excessive pressure
which may occur due to high actuator loads.
3. Flow control valve: To control fluid rate in various line of a hydraulic circuit to
control actuator speeds depends on flow rates.
Classification
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Hydraulic and Pneumatic Question Paper
1. gate valve
2. Plug valve
3. Needle valve
4. butterfly valve
5. Non-return valve
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Hydraulic and Pneumatic Question Paper
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Hydraulic and Pneumatic Question Paper
When the fluid enters the back end of the cylinder during its extension stroke piston
moves towards the right. Exhaust flow passes freely out of the cylinder.
During reaction stroke, the fluid enters the rod end side of the piston through a small
opening. This makes the piston move left. Also, the exhaust flow passes freely out of the
cylinder from the left. Direction control valves & flow control valves are used.
6. Write a note on pipe material, types of fittings & connectors in the fluid
system.
Answer:
1. Pipe materials:
The pipe which is used in the fluid power system is made of steel, copper, brass,
aluminum stainless steel.
Steel pipe & tubing are expensive & used in many hydraulic & pneumatic
system.
Copper pipe & tubing are used fluid power lines.it is having high resistance to
corrosion & easily drawn or bent.
Stainless steel tubing is used in certain areas of many aircraft fluid power
systems.
2. Types of fittings:
The end of the metal tube is attached to the port of the hydraulic elements by means of
various adapters called fittings. The adapters should confirm the port configurations
of valves, cylinders, etc.
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Hydraulic and Pneumatic Question Paper
3. plain female
4. Plain male
3. Types of connectors:
Types of connectors are provided in order to connect the lines of components to the
system & to connect sections of line to each other.
1. Welded connectors
2. Flange connectors
3. Brazed connectors
4. Threaded connectors
5. Flared connectors
6. Formed connectors
7. Screwed connectors
8. Clampcouplings
Pneumatics:
It is derived from Greek word Pneuma, which means air, wind or breath.
It can be defined as the branch of fluid power in which gas is used as a fluid.
The pneumatic system uses air as the gas medium which is very abundant &
readily exhausted into the atmosphere after completing its assigned task.
Applications of pneumatics :
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Hydraulic and Pneumatic Question Paper
Answer:
A single-stage reciprocating when the piston moves downwards during the suction
stroke, the air is drawn into the cylinder through the inlet valve.
No, when the piston moves upward during the delivery stroke the air is compressed
and the pressure increases till it reaches the discharge pressure.
At this stage-discharge valve opens and the air is delivered to the container and once
again the same cycle is repeated. But sometimes, the air is required at high pressure.
In such cases either we have to employ a large pressure ratio or compress the air in two
or more cylinders in series with an intercooler between the stages are used.
First, the fresh air is sucked from the atmosphere through the suction filter and inlet
valve in low pressure (LP) cylinder during its suction stroke.
The air after compression in the LP cylinder (ie. first stage) is forced into the intercooler.
Now the air is cooled at constant pressure.
After this, the air is sucked into the high pressure (HP) cylinder during its suction
stroke, and finally, the air is further compressed (i.e. second stage) to the desired level
and is fed to the receiver through the condenser by opening the outlet valve.
Advantages of multi-staging:
Answer:
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Hydraulic and Pneumatic Question Paper
It consists of two ports connected to each other with passages, which are
connected & disconnected.
In one external spool position, Port A is open to port B, the flow path through the
valve is open.
Inthe other external, the large diameter of the spool closes the path between A &
B, the flow path is blocked. It gives an on-off function.
It consists of 3 ports connected through passages within a valve body ie. port A,
port P &port Ex.
If port A is connected to an actuator, port P to a source of pressure & port Ex is
open to exhaust, the valve will control the flow of air to port A
The function of this valve is to pressurise & exhaust one actuator port. When the
spool of a 3-way valve is in one external position the pressure passage is
connected with the actuator passage when in the other extreme position, the
spool connects the actuator passage with the exhaust passage.
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Hydraulic and Pneumatic Question Paper
These valves are having four different flow paths within the valve body.
To perform this function, spool connects the pressure port with one actuator
port. At the same time, the spool connects the other actuator port with the
exhaust port.
Five ports are one pressure port, two actuator ports, & two exhaust ports. These valves
provide the same basic control of flow paths as four-way directional valves have
individual exhaust ports.
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Hydraulic and Pneumatic Question Paper
Ans:
1. Constant discharge.
2. Spur or helical gears are used.
3. Only one gear is driven externally.
4. Oil is discharged due to the meshing of gears.
5. Gears are in actual contact with each other.
Lobe pump :
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Hydraulic and Pneumatic Question Paper
Hydraulic system :
1. Speed is limited
2. Operates at high pressure
3. Pump is necessary
4. No noise is produced
5. Resistances to fluctuating load
6. Suitable for feed movement in m/ c tools
7. Most expensive
8. Oil as a media to transfer energy
9. Cavitation is a big problem
Pneumatic system :
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Hydraulic and Pneumatic Question Paper
Answer:
Fluidics: Fluidics is a part of the fluid power technology that develops a totally reliable
hydrauic& pneumatic control system using fluid flow phenomena in components &
circuits to perform a variety of control functions such as sensing, logic, memory &
timing.
The subject which deals with the area of fluid logic is called fluidics.
1. Specific need of control engineering forced engineerings for a solution within the
fluid power system.
2. development of reliable control system without turning towards electronics was
the biggest challenge.
3. Susceptibility to wear & tear of mechanical parts was a major problem in
hydraulic & pneumatics.
13. Pilot controlled double acting cylinders using 4/2 D.C valve in
pneumatics.
Answer:
With a large capacity pneumatic valve, the operating force requires to move the valve
can be large. If the required force is too high for manual operation or solenoid, a two-
stage process called pilot operation is used.
the principle operation of pilot operated valve is shown in the figure. Valve 1 is a main
operating valve that is used to move the ram. The operating force required to move the
valve is too high. Threrfource a direction by a pilot valve is used. A second smaller
valve 2 Known as the 4/2 pilot valve has been added to allow the main valve to be
operated by system pressure.
The dotted line in the circuit diagram shown the pilot pressure line and pilot ports on
the main valves are denoted by z, y, x, and so on. The pilot port ′z′ is depressurized
when the 4/2 pilot valve is de-energized and the ram is retracted. When the start button
is pressed, valve 2 changes over-pressurized Z, by the impulse of air energy, causing
valve 1 to energize and the ram to extend. The signal pilot valves are also termed the
signal generator. This signal is provided to the pilot-operated valve by means of an air
impulse.
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Hydraulic and Pneumatic Question Paper
Answer:
The figure has shown a pilot operated valve consists of main spool, a valve body
a spring & a second adjusting screw.
In this valve, the fluid flows freely through the primary passage to operate the
first phase until the pressure setting of the sequences valve is reached. When the
spool lifts flow floe is divorced from the secondary port to operate the second
phase.
Answer: The figure is shown a simple piston pump called a positive displacement or
hydrostatic pump.
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Hydraulic and Pneumatic Question Paper
As the piston driven down, the inlet valve opens and a volume of fluid
(determined by the cross-section area of the piston and the length of stroke) is
drawn into the cylinder.
Next, the piston is driven up with the inlet valve closed and the outlet valve
open, driving the same volume of fluid to the pump outlet.
This pump is used for high passage and low discharge application.
Advantages :
Answer:
Working
Once the pump starts, the gears also start meshing with each other causing the tooth
space of the gears to be evacuated one after the other. The oil at atmospheric pressure
enters the chamber through the inlet port.
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Hydraulic and Pneumatic Question Paper
The oil is further carried around the housing in chambers due to gears rotation towards
due to teeth mesh which reduces the volume between mating teeth.
Since the pump has a positive internal seal against leakages, the oil positively
discharges into the outlet port.
Answer:
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Hydraulic and Pneumatic Question Paper
Answer:
Spring applies force on the piston. As the fluid is pumped into it, the piston compresses
the spring & thus energy is stored in the spring.
Ans:
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Hydraulic and Pneumatic Question Paper
Working: As each blade moves fast the inlet passage, compression begins due to the
decreased volume between the rotor and the casing. When each blade arrives at the
delivery passage, delivery begins.
Unlike roots blower, some or all of the compression is obtained before the trapped
volume is opened to delivery.
Further compression takes place due to the backflow of air from the receiver which
occurs in an irreversible manner.
Answer:
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Hydraulic and Pneumatic Question Paper
Answer:
As the name indicated it consists of a diaphragm, secured in the shell. The diaphragm
acts as an elastic separator between the oil and gas. A shut-off button is provided at the
base of the diaphragm. It covers the inlet of the line connection when the diaphragm is
fully stretched. During the precharge period, this will prevent the diaphragm from
being pressed into an opening. On the gas side, the screw plug allows control of the
charge pressure and charging of the accumulator by means of a charging device.
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Hydraulic and Pneumatic Question Paper
Ans: Hydraulic system: It uses the liquid as its medium. Six basic components are as
follows:
Ans:
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Hydraulic and Pneumatic Question Paper
In the design of the DC valve, 5 openings are preferred. This ensures easy exhausting of
the valve. In position-1, when the spool is actuated towards the outer direction port 'P'
connects to 'B' and 'S' remains closed while A gets connected to 'R'. In Position-2 when
the spool is pushed in the inner directions, port P and A gets connected to each other
and B to S while port R remains closed.
Ans: The intensity of pressure at any point in a fluid at rest is the same non-directions.
2) Consider a hollow sphere having small holes on its sides with a piston inside. The
sphere is filled with water, as the piston moves, the water spurts out of all the holes.
The piston exerts equal pressure on the surface of the water. As a result, part of the
water is squeezed out of the sphere in the form of jets flowing out of all the holes
simultaneously illustrated the pressure transmitted is the same in all directions.
3) The liquid flows into the large container at the bottom, the pressure pushes the liquid
equally up into the tubes above the container. The liquid rises to the same level in all of
the tubes, regardless of the shape or angle of the tube. Ex: Hydraulic jack
1. With the help of an accumulator, the energy can be stored, for used when the
power is off.
2. It offers a wide range of speed control which is difficult to be obtained on the
machine drive.
3. it doesn't require any lubrication, as it is very much required in all mechanical
drives. as a result, parts don't wear out rapidly.
4. Its maintenance is very simple. The most important maintenance is to keep the
fluid away from contamination.
5. It provides the great flexibility of locating different parts at widely separated
places.
6. It offers a wide range of speed control which is difficult to be obtained on the
machine drive.
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Hydraulic and Pneumatic Question Paper
Answer: Relief valves are automatic valves used on systems lines and equipment to
prevent over pressurization.
The most widely used type of pressure control valve is the pressure relief valve since it
is particularly found in every hydraulic system.
The figure shows a simple pressure relief valve consisting of poppet held seated in the
valve body by a heavy spring.
The valve remains closed when the inlet pressure is less than spring pressure.
When the system pressure reaches a valve that is high enough to force the poppet off its
seat this permits the flow from the outlet to the tank until the system pressure drops to
set the valve.
An adjacent screw is provided to vary the spring force so that the valve can set open
any pressure within a specified range.
27. Explain the construction & working of the single acting cylinder of the
pneumatic system.
Answer:
The flow of oil is acting on one side of the piston is called the single-acting cylinder.
It consists of piston places inside a cylinder called a barrel, a rod attached to the one end
of the piston, which extends outside the cylinder.
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Hydraulic and Pneumatic Question Paper
The compressed air is supplied on only one side (left side) of the piston face and the
other side is open to the atmosphere, the cylinder can produce work in only one
direction.
The return movement of the piston is affected by a built-in spring or by the application
of an external force.
The built-in spring is designed in such a way that it will come back to its start position
with sufficiently high speed under no-load conditions.
The exhaust air on the piston rod side is exhausted through the drain hole. The single-
acting cylinder is used in cutting operation ejecting parts, clamping of the workpiece,
feeding, and lifting.
Ans. It states that "The intensity of pressure at any point n a fluid at rest, is the same in
all direction".
It can also be stated that "when pressure is applied to the fluid which is confined to flow
in all the directions, then that fluid transmits the same pressure in all direction at the
same rate".
Mathematically,
Px = Py = Pz, where
Px = Intensity of horizontal pressure on the element of the liquid
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Hydraulic and Pneumatic Question Paper
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