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What is an accumulator ? Why accumulator is necessary for huge hydraulic pressers ?

makes available to the system whenever required. Necessity of accumulator for every huge hydraulic press: Oil requirement of the system is not continuous but intermittent. A hydraulic press needs the oil only during the lifting operation. While, during the lowering of load, holding the load or during idle period, it doesn’t not require any supply of oil. During such period, the hydraulic pump has to stop or delivered oil must be drained back to the sump. But frequent starting and stopping of pump is not desirable as it reduces the pump life.

Draw and explain working of pressure reducing valve.........

Draw and explain working of pressure reducing valve. The main function of pressure reducing valve is to reduce the pressure in particular branch of the circuit to different level as demanded by consumer in that branch. Construction: It consists of spool and spring housed in the bore of valve body. Spring compression can be adjusted by pressure setting screw. Port P is pressure port connected to pump. Port A is consumer port requiring reduced pressure.

 

State the four merits and demerits of using a rubber hose in pneumatic circuit..............

Merits: 1)Well equipped with quick connect or disconnect end fitting 2)Can be manufactured in long lengths 3)Capable of withstanding to very high pressures. 4)They can absorb very heavy shocks tha rigid tubes. Demerits: 1) Very poor in abrasion resistance 2) Poor in resisting whether condition. 3) Initial cost is very high 4) They can damage due to incompatible oil

Discuss pilot operated check valve with neat sketch............

When pilot signal of pressurized oil is used to control movement of poppet in the check valve, it is called as pilot operated check valve. It is used when no flow characteristics of the valve is desired only for a portion of the system cycle. Figure shows the pilot operated check valve. A pilot piston is introduced below moving poppet. This pilot piston can move up by introducing pilot signal. Working: In normal position there is no flow from (A) to (B) because the movable valve poppet has blocked the flow. Now pilot signal is given through port (C).

What is seal ? Classify seals according to shape. State the factors for seal selection.........

Seal: The seal is an agent or element which prevents leakage of oil from hydraulic elements and protects the system from dust and dirt. Classification of seals based on shape:- a) ‘O’ Ring seal b) ‘V’ Ring seal c) U-packing seal d) T- ring seal e) Cup seal

Factors for seal selection: 1) Type of fluid used in system 2) Maximum temperature of system in working condition 3) Functional reliability expected 4) Cost of seal 5) Working pressure of system 6) Environmental condition

 

Explain any two mounting methods of cylinder. ................

1) Centreline mounting Centreline mounts are used to take care of thrust that can occur linearly or along a centreline with the cylinder. Proper alignment is essential to prevent compound stresses that may cause excessive friction and bending, as piston extends. Additional holding strength may be essential with long stroke cylinders. 2) Foot mounting It consists of mounting the cylinder with the help of side end lungs or side covers. These mountings are used where cylinders are to be mounted on to surface parallel to the axis of cylinder

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