Draw & explain in brief hydraulic bleed off circuit.

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written 5.8 years ago by

teamques10 ★ 68k

• modified 5.8 years ago

Fig shows typical bleed off circuit. Here, the flow control valve is arranged to bypass a part of the pump output directly to the tank. When the flow control valve is completely closed, the full flow from the pump would go into the cylinder. However, the moment the flow control valve is opened, some portion of the pump outlet will be bledoff and the cylinder starts to slow down.
Adjusting the size of the opening will bleed off any amount necessary to control the speed of piston.Unlike the meter-in and meter-out circuit there is no excess flow going over the relief valve. The excess oil bleed-off circuits are more efficient in energy saving and work in a cooler environment.
However, bleed off circuit provides less accuracy is speed control, because they don‟t compensate for any change in fluid losses due to pressure change. Here the measured flow goes to the tank rather than the cylinder.
This makes the cylinder speed subject to change with the pump delivery and hydraulic system leakage which occur as work load pressure changes. To minimize these effects, it is recommended to bleed-off no more than half the pump delivery and avoid using a bleed-off circuit completely where there is a wide fluctuation is the load pressure.In general, bleed-off speed control is best employed when the majority of the pump outlet is utilized by the cylinder and only a small percentage is bypassed.
Also it is employed in systems where the pressure is reasonably constant and precise speed control is not the criteria.

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