The bleed-off circuit is the third basic circuit, which controls neither the flow going to the actuator not flow returning from the actuator but control the diverted part of the fluid to control the flow.
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Bleed Off Circuit Diagram
In this type of circuit flow control valves are placed in the bypass lines. The cylinder speed, in this case, is determined by the difference between the pump deliver flow and the flow being directed to the tank through the flow control valve.
The bleed-off circuit controls the fluid which is diverted for controlling the flow.
Advantages of bleed-off circuit
Unlike the meter-in circuit and meter-out circuit, there is no excess flow going through the pressure relief valve, hence the system is more efficient and energy-saving as well the hydraulic fluid is not heated due to flow through the relief valve.
Disadvantages of bleed-off circuit
- The bleed-off circuit provides less accuracy in speed control because in these circuits metered flow goes to the tank rather than to the cylinder.
- In such types of circuits, an individual pump should power each cylinder.
- The bleed-off circuit is not sensitive enough to compensate for very small flow such as those encountered in precise boring operations.
Applications of bleed-off circuit
- Bleed-off circuits are applied where pressure is reasonably constant and precise speed control is not the prime requirement.
- These circuits are widely used in broaching machines, shapers, planers, etc where a large quantity of fluid is to be used, and a small percentage is bypassed.