The Rexroth tech manual does't give any kind of procedure for adjusting the pressure controls and we had some well intentioned but uninformed knob twisters make adjustments. Does anyone have any advise on how to do this properly?
What's the application? What is the pump being used for?
From the Rexroth manual, the A4VS40DR the A4VS is a 'Variable pump, swashplate design, for industrial drives' and the DR denotes 'Press. control, single sided operation'. Is the pump used with a variable speed (VS???) drive or just an induction motor running at a constant speed?
Is the output of the pump also protected with a pressure relief valve?
In general, an axial piston pump with a swashplate design just requires adjusting the swashplate position to set the output pressure, presuming there is not excessive flow through the pump. There have been cases of relief valves improperly relieving and causing excessive flow through the pump and an inability to set the pump output pressure. One way to determine if there is excessive flow is to monitor the power being consumed by the motor; if the power (current draw for an induction motor) is excessive, then it's a safe bet the flow through the pump is higher than rated.
If there is a relief valve being used to protect the pump or the components downstream of the pump, it's very common for people to incorrectly assume that the relief valve is used to set the pump discharge pressure. The relief valve is pressure setting must be above the pump output pressure setting, and the only way to check the relief valve operation is to increase the pump output pressure until the relief valve starts relieving, then adjust the relief valve if necessary. Then, back down the pump pressure output adjustment to set the pump output pressure.
There are also applications with redundant pumps feeding a common header, with check-valves to prevent back-flow through the "stand-by" pump. These check valves have failed and caused problems, again, usually because of excessive flow.
Thanks for your response and sorry for the delay in my response, but my recent stay in the hospital took me off line for a while.
The pump provides bearing/shaft lift oil for a 200 MW steam turbine. So the system pressure/flow requirements are pretty constant. There is a relief valve, which has no apparent flow through it so it's set above the operating pressure.
There is also a pressure adjustment on the outlet of the pump which is maxed out. Then there are two other adjustable devices on either side of the pump which appear to be pressure regulators. I think these adjust the swashplate angle. The motor runs at a constant speed.
I have noticed that there's flow through the casing drain, which is located between the presumed swashplate adjusters. I don't know if flow through this drain is normal or not.
There is a single nut adjustment on the control valve, this will set regulating, or system pressure. The 2 adjustments you are talking about (on the ends of the control piston) are minimum and maximum volume stops, and under normal circumstances should be backed out all the way. The pump will vary the swash angle based on the DR pressure control. If pressure drops, the pump comes on stroke, if pressure reaches the DR control setpoint, the pump comes off stroke.
In your application you may want to set the minimum volume to ensure proper lubrication of the equipment.
Also, don't forget to set your system relief about 10-15% higher than your DR control. To properly set this you will need to walk the relief and DR control adjustments in until you are sure the relief is closed, and the DR is regulating the pump to the desired relief setpoint, then back the relief out until it just cracks open at this pressure.
Then finally set your system pressure via the DR control.
The case drain is of course supposed to see flow! The pump is self lubricating, and this flow cools and flushes the bearings. Ensure that there is no pressure on the case drain line (no restrictions back to reservoir).
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