The role of the pressure reducing valve is to protect a part of the hydraulic circuit by reducing the pressure.
- Protect the brake of a hydraulic motor.
- Provide reduced pressure to hydraulic joystick controls.
- Reduce the pressure of a control circuit.
There are two types of pressure reducting valve:
- Direct action.
The direct acting pressure reducer is composed of a setting spring (item 8), adjustable by the screw (item 9). The spool (item 6) is controlled by the channel (item 7). The channel (item 10) provides external drainage of the spring box.
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3- Operation (cylinder output phase)
The symbol B is representative of the mechanical figure A.
The fixed displacement pump (item 1) driven by the engine (item 2) provides a flow rate of 30l / min.
The hardness of the setting spring of the pressure relief valve (item 3) is set to 200 bars.
The hardness of the setting spring (ref 8) of the pressure reducer is adjusted by the screw (item 9) to 100 bars. The pressure reducer is a valve normally open at rest, put in series on the circuit and controlled on the output.
The oil from the pump moves the cylinder piston (item 5).
The pressure required to move the cylinder is 50 bars found on the manometers (M1 & M2), pressure that is created by the mechanical strength of the load.
The pressure is established on the spool (item 6), but the mechanical stress of the setting spring (item 8) is greater than that of the pressure exerted on the surface of the pusher (item 6).
The pressure reducer remains open and all the flow of the pump (item 1) is directed towards the cylinder (item 5).
To note: The pressure reducers are externally drained to decompress the spring box. Indeed, there is a pressure on each side of the valve (M1 & M2) which prevents spool leak decompress (item 6) in internally.
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4- Operation (cylinder phase in mechanical stop)
The cylinder (item 5) is in mechanical stop and the pump (item 1) is driven by the motor (item 2) to the working regime.
The oil instantly accumulates in the cylinder (item 5) and the pressure rises in the circuit.
The pressure exerted on the spool (item 6) reaches the value of the spring (item 8) or 100 bars.
The flow moves the spool (item 6) and closes the oil passage from A to B.
At this moment the pressure in the cylinder cannot increase.
The flow is accumulated at the inlet of the pressure reducer. It is evacuated by the pressure relief valve (item 3) under a pressure of 200 bars.
To note: If a leak appears on the piston of the cylinder (item 5), the pressure in M2 will tend to drop, the spool (item 6) will move slightly and let the flow necessary to compensate for this leakage without exceeding 100 bars.
5- Adjusting the pressure reducer
It is imperative to install a pressure gauge after the pressure reduction.
- Loosen the pressure reducer.
- Start the pump, engine working speed (max).
- Tighten the pressure relief valve by checking the setting (200 bar) on the pressure gauge installed at the pump outlet (M1).
- Tare the pressure reducer. At 50 bars the cylinder moves, at this moment it is necessary to stop the adjustment and wait until the cylinder is in mechanical stop.
Finish setting the pressure reducer at 100 bars read on the pressure gauge M2.
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