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Scheet N° 7

Constant pressure pump adjustment

(Hydraulic expertise)




1- Open circuit pump type A4VSO (Rexroth)


The Rexroth "A4V" pump is a variable displacement piston pump that can be used in open circuit (A4VSO) and loop circuit (A4VSG).

1.1 In the photo above, we can see that the pump has three connections:

A rigid suction pipe of big size. In general, piston pumps suck very badly, it is necessary either to force-feed them or to put them in charge (oil enters the pump by gravity).

A hose delivery hose on the side of the pump.

A hose drain hose on the underside of the pump needed to evacuate internal leaks as well as the flow generated by the movement of the servo-piston when the pump changes displacement.

Note: It is common for hydraulic systems with constant pressure pumps to perform a flushing.

That is to say put in place a flow of fresh oil through the drain lines to cool the box of pumps that tend to heat when they are waiting for cycle.

1.2 On the picture above, we find two displacement stop screws (one on each side of the servo piston) and a screw for adjusting the flow cancellation.

Note: the flow cancellation of the pump can be called:

     - Compensator

     - PC valve (Constant Pressure)

     - DR valve (Druck Régulator)

2- Pressure relief valve with pilot action with bypass.



In the photo above, we find the manifold block on which is installed the pilot operated pressure relief valve   with by-pass function, and the pressure gauge that will allow us to make adjustments (pump - pressure relief valve)





  1- Loosen the pressure relief valve and pump flow cancellation

  2- Start the pump

  3- Operate the bypass directional valve (EVD)

  4- Tighten the pump setting (flow cancellation) to convert it to a fixed displacement pump

  5- Set the pressure limiter to 200 bars

  6- Set pump flow cancellation at 180 bars

Note: It is essential to set the pressure relief valve above the pump's flow-canceling pressure to avoid rolling the oil into the pressure relief valve.

The pressure relief valve is indispensable in the circuit. Adjusted in shockproof, it remove the pressure peaks created by the reaction times of the pump tray.

Caution: On large hydraulic systems it is possible that the pressure relief valve is undersized and does not pass the entire flow of the pump.



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