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
- Resisting lightly due to viscosity
- Ability to flow and take the shape of the container in which it is filled.
Pneumatics means gas or air. It can be defined as a branch of fluids power in which gas is used as a fluid.
Hydraulics and Pneumatics Question paper
1. Explain Basic methods of transmission of power in brief.
Methods of power transmission: There are basically 3 of transmission of power & they are :
- Mechanical & Electrical mode
- Hydraulic system
- Pneumatic system
(a) Mechanical & Electrical mode: The power that drives a machine is transmitted through.
- By using chain which mounted on sprockets.
- By using belt or rope mounted on pulleys. This is driven by the electric motor.
- By means of gears form a separate electric motor attached to each machine.
(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.
Definition of pump: The pump is a device that is used to pump fluid. A pump converts mechanical energy into hydraulic energy.
purpose of pump: Mechanical energy can be supplied through an electric motor. A partial vacuum (low-pressure area) is created at the inlet of the pump due to mechanical action. Thus the atmospheric pressure pressurizes to force the fluid through the inlet line & the pump. The pump forces the fluid into the hydraulic system.
Classification of Pumps.
3. Sketch and explain external gear pump.
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.
- The second gear is driven as it meshes with the driven gear.
- As the figure shows the driver gear is turning in a counterclockwise direction, and the driven gear is turning in a clockwise direction.
- The inlet port is connected to the fluid supply line, and the outlet port is connected to the pressure line.
- As the teeth pass the inlet port, the liquid is passed between the teeth & housing. This liquid is carried around the housing to the inlet port.
- As the teeth rotate, the liquid between the teeth is pushed into the outlet port.
- This action produces a positive flow of liquid into the system.
4. How are the control valve classified? write the classification of the control valve.
The control valve is classified into 3 types depending upon the function they perform:
- Directional control valves: Identify the path through which fluid passes in a given circuit.
- Pressure control valve: It protects the system against the excessive pressure which may occur due to high actuator loads.
- Flow control valve: To control fluid rate in various line of a hydraulic circuit to control actuator speeds depends on flow rates.
Types of pressure control valves:
- Pressure Relief valve
- Pressure Reducing Valve
- Counter-balance valve
- Pressure switch & forces
Types of Direction control valve:
- Sliding spool types
- Rotary spool types
Types of flow control valves:
- gate valve
- Plug valve
- Needle valve
- butterfly valve
- Non-return valve
5. Explain with a neat sketch construction & working of the double acting cylinder.
The figure shows the Double acting cylinder.
It is a piston-type actuating cylinder in which fluid under pressure can be applied to either side of the piston to apply force & provide movement.
Construction of double-acting cylinder
- The cylinder barrel is made of steel tubing which is seamless.
- The inner surface is perfectly boned.
- The piston is manufactured by ductile iron.
- U-packing is used to prevent leakage between the piston & the barrel.
- Port is located in ends caps.
- They are secured to the barrel by tie rods.
- Piston ends are tapered. It ensures shock-free operation.
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.
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.
The following are the types of fittings:
- Female threaded – parallel & taper
- Male threaded – parallel & taper
- plain female
- 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.
There are different types of connectors & they are: W-F-B-T-F-F-S-C
- Welded connectors
- Flange connectors
- Brazed connectors
- Threaded connectors
- Flared connectors
- Formed connectors
- Screwed connectors
7. Mention the applications of pneumatics in the engineering field.
- 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 :
- In brack system of automobiles, railway coaches, wagons, printing presses.
- In operation of machine tools.
- Air tools like pneumatic drilling, punching riveting etc.
- To drive liner & rotary actuators
- In stamping
- In metal forming and filling.
8. Draw a piston type reciprocating air and explain its working.
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:
- Increase in compressor efficiency.
- Reduction in input power requirements.
- Increase in volumetric efficiency.
- Reduction heat due to compression by using intercoolers.
9. Mention types of the directional control valve and method of their actuation symbols.
Types of the directional control valve (DCV) :
- Two-way directional valve
- three-way directional valve
- Four-way directional valve
- Five port directional valve
1. Two-way directional control valve:
- 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.
2. Three-way directional valve :
- 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.
3. Four-way Directional valve :
- 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.
4. Five Port Directional valve :
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.
10. Differentiate external gear pump with lobe pump.
External gear pump :
- Constant discharge.
- Spur or helical gears are used.
- Only one gear is driven externally.
- Oil is discharged due to the meshing of gears.
- Gears are in actual contact with each other.
Lobe pump :
- Discharge can vary.
- Lobe is used.
- Both the lobe are driven externally.
- Oil is discharged due to rotation of lobes.
- Lobes do not contact with each other.
11. Mention differences between hydraulic & pneumatic systems.
Ans: Differences between hydraulic & pneumatic systems:
Hydraulic system :
- Speed is limited
- Operates at high pressure
- Pump is necessary
- No noise is produced
- Resistances to fluctuating load
- Suitable for feed movement in m/ c tools
- Most expensive
- Oil as a media to transfer energy
- Cavitation is a big problem
Pneumatic system :
- Very high speed is possible
- operates at low pressure
- No pump at all
- A lot of noise is produced
- Non-resistant to fluctuating load.
- Unsuitable for teed movement.
- Less expensive
- Air as a media to transfer energy
- No cavitation problem
12. Define fluidics & mention the needs for fluidics.
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.
Need for Fluidics:
- Specific need of control engineering forced engineerings for a solution within the fluid power system.
- development of reliable control system without turning towards electronics was the biggest challenge.
- 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.
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.
14. Sketch & explain pilot-operated sequence valve.
- When the operation of two hydraulic cylinders is required to be performed in sequence by using a single direction valve called pilot-operated sequence valve is used.
- 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.
15. Explain positive displacement pump & mention its advantages.
Answer: The figure is shown a simple piston pump called a positive displacement or hydrostatic pump.
- 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.
- widely used in the hydraulic system
- Very high pressure can be generated.
- High volumetric efficiency.
- Greater flexibility of performance.
16. Explain with neat sketch gear type motors.
This figure shows the construction of the gear pump.
- It consists of two meshed gears.
- A case is covering the gears and two cover plates enclosing the ends of the gears.
- Gears are mounted on a shaft supported by the bearing in the end covers.
- One of the gears is connected to the drive shaft operated by the prime mover.
- Two ports, inlet and delivery are located on the opposite ends of the gear casing.
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.
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.
17. Explain construction & working of the single acting cylinder.
Construction and working
- The piston is housed in a barrel.
- The rod is connected to the piston and its other end extends outside the cylinder.
- Oil pressure is fed only on one side of the cylinder either during extension or retraction.
- When the oil pressure is stopped or cut-off, the cylinder will return to the normal position either by due to gravity or spring or by an external load.
- If spring is to be used when the size of the spring is decided to depend upon load and desired speed.
18. Explain with neat sketch spring load accumulator.
In a spring-loaded accumulator, the piston is preloaded with a spring.
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.
It is released as it is required by the demand of the system. This type of accumulator delivers only a small amount of oil at low pressures.
19. Explain with neat sketch vane compressor.
Construction: A simple vane compressor consists of a rotor mounted eccentrically in the body and supported by ball and roller bearings in the end covers of the body. Blades are mounted on the slotted rotor and are usually non – metallic, made of fiber or carbon.
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.
20. State the advantages and disadvantages of the poppet valve.
Advantages of poppet valve:
- The poppet valve is simple and also easy to operate.
- It is suitable for high-pressure duties and indirect actuation.
- High response relative insensitivity to contamination.
- No leakage.
- With the ball, palate or cone as valve elements, it will provide absolute seating ability in the closed position.
Disadvantages of poppet valve:
- Not for large valve size.
- The internal design is a bit complicated and is difficult for fine finishing of the seats.
21. Explain the construction and working of Diaphragm Accumulator.
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.
22. Sketch and explain the basic hydraulic system.
Ans: Hydraulic system: It uses the liquid as its medium. Six basic components are as follows:
- A tank (reservoir) to hold the hydraulic oil.
- A pump to force the oil through the system.
- An electric motor or another power source to drive the pump.
- Valves to control oil direction, pressure and flow rate.
- An actuator to convert the pressure of oil into mechanical force. For linear motion, cylinders are used. For rotary motion, motors are used.
- Piping to carry oil from one location to another.
23. What in 5/2 DCV? Explain with neat sketch.
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.
24. Define Pascal’s law & Its Applications.
Ans: The intensity of pressure at any point in a fluid at rest is the same non-directions.
Applications of Pascal law:
- The mode of transmission of force in a soli and in a liquid is as shown in fig.
Example: pressures, Injection molding, Machine.
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
25. What are the advantages of a hydraulic system?
Answer: Advantages of a hydraulic system:
- With the help of an accumulator, the energy can be stored, for used when the power is off.
- It offers a wide range of speed control which is difficult to be obtained on the machine drive.
- 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.
- Its maintenance is very simple. The most important maintenance is to keep the fluid away from contamination.
- It provides the great flexibility of locating different parts at widely separated places.
- It offers a wide range of speed control which is difficult to be obtained on the machine drive.
26. Sketch & explain pressure relief valves.
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.
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.
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.
28. What are the common faults in the hydraulic system?
Ans. Common faults in the hydraulic systems are:
- Shape noise in the system.
- The steep rise in the oil temperature.
- Reduced speed of travel of machine tool elements.
- Feed rates.
- Slow response to control.
- Excessive leakage in the system.
- Cavitation of pumps.
- The high rate of seal failure.
- No supply from the pump.
- Excessive loss of system pressure.
29. Explain the Pascal’s Law with the equation.
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”.
- Px = Py = Pz, where
- Px = Intensity of horizontal pressure on the element of the liquid
- Py = Intensity of vertical pressure on the element of the liquid
- Pz = Intensity of pressure diagonal of the triangular elements of the liquid
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