JNTU
JNTU B.Tech IV Year FLUID POWER SYSTEMS Previous Question Paper (July/August - 2022 - R18)
Answer any five questions. All questions carry equal marks.
Main
Differentiate between hydraulic and pneumatic systems for control units with sufficient examples.
Answer
Hydraulic and pneumatic systems differ primarily in the working medium used to transmit power and their operational characteristics. Hydraulic systems use incompressible liquids (typically mineral oil) to transmit power, allowing for high force density and precise control, whereas pneumatic systems use compressible gases (typically compressed air), making them suitable for high-speed, low-force applications.
| Feature | Hydraulic System | Pneumatic System |
|---|---|---|
| Working Medium | Liquid (Oil) | Gas (Air) |
| Operating Pressure | High (up to 700 bar) | Low (up to 10 bar) |
| Compressibility | Incompressible | Compressible |
| Response Speed | Slow and steady | Fast |
| Lubrication | Self-lubricating | Requires external lubricators |
| Applications | Earthmoving equipment, presses | Automation, packaging, hand tools |
With a suitable sketch, explain the basic components required in a hydraulic system.
Answer
A basic hydraulic system consists of several essential components that work together to convert mechanical energy into fluid power and then back into mechanical motion. The primary components are:
- Hydraulic Power Unit (HPU): Includes the reservoir (tank) for fluid storage, a pump driven by an electric motor to generate flow, and a relief valve for pressure regulation.
- Control Valves: These include directional control valves to manage the path of the fluid, pressure control valves to maintain system limits, and flow control valves to regulate actuator speed.
- Actuators: Hydraulic cylinders (linear motion) or hydraulic motors (rotary motion) that convert the hydraulic energy back into mechanical work.
- Transmission Lines: Hoses and pipes that carry the pressurized fluid between components.
- Accessories: Filters to clean the fluid, heat exchangers to maintain temperature, and pressure gauges for monitoring.
In operation, the pump draws oil from the reservoir and delivers it at high pressure. The directional control valve directs this fluid to the actuator, causing it to extend or retract, while the relief valve returns excess fluid to the reservoir if the pressure exceeds the set limit.
What is meant by the K factor of a valve or fitting? “To minimize pressure losses, the K factor of a valve should be made as small as possible”. True or false? Justify.
Answer
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Illustrates the operation of an external gear pump. Obtain the expressions for volumetric displacement, theoretical flow rate and volumetric efficiency.
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What is hydraulic actuator? Classify hydraulic actuators based on their principles of operation.
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Describe the construction and working of double-acting cylinders with a piston rod on one side and on both sides.
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A pressure relief valve contains a poppet with a 4.20 cm2 area on which system pressure acts. During assembly a spring with a spring constant of 3200 N/cm is installed in the valve to hold the poppet against its seat. The adjustment mechanism is then set so that the spring is initially compressed 0.50 cm from its free-length condition. In order to pass full pump flow through the valve at the PRV pressure setting, the poppet must move 0.30 cm from its fully closed position. Determine the cracking pressure and full pump flow pressure.
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What is the difference between closed-circuit and open-circuit hydrostatic transmissions?
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Explain how valves are actuated using manual, mechanical, fluid pilot, and electric solenoid methods.
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Describe in detail about the construction, principle, working and applications of regenerative cylinder circuit.
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Explain the various types of compressors used in pneumatic applications.
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What is a time delay valve? What are its components? Explain the principle of operation and applications of a time delay valve.
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List and explain seven basic electrical devices used in electro pneumatics.
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Draw the Displacement-Step Diagram and Displacement-Time Diagram for a pneumatic drilling operation.
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