Rexroth A10VSO Pressure Compensator Adjustment

The A10VSO is a swashplate axial piston variable pump for open circuits, and almost every service call that starts with the pump will not build pressure, or it runs hot at idle, ends at the controller on the end cap. This guide covers setting the DR pressure compensator and the DFR / DFR1 standby on an A10VSO Series 31.

First, confirm which controller you have

The A10VSO type code tells you which control device is fitted. It is position 05 in the code, immediately after the size. Adjusting the wrong screw is the most common mistake on these pumps.

Code	Control device	What is adjustable
DG	Two-point control, direct operated	No pressure adjustment. Swivels to max or min only.
DR	Pressure controller, hydraulic	One screw: maximum system pressure.
DRG	Pressure controller, remote controlled	Local max pressure, plus an external relief valve piped to port X.
DFR / DFR1	Pressure and flow controller	Two screws: pressure as DR, and differential pressure for standby.
DFLR	Pressure, flow and power control	As DFR, plus a factory-set power curve.
ED / ER	Electrohydraulic pressure control	Pressure set by solenoid current, with an adjustable hydraulic pressure cut-off.

Setting ranges, A10VSO Series 31

Parameter	Value (bar)	Value (psi)
Nominal pressure	280 bar	approx. 4,060 psi
Maximum pressure	350 bar	approx. 5,075 psi
DR pressure control setting range	20 to 280 bar	approx. 290 to 4,060 psi
DR standard factory setting	280 bar	approx. 4,060 psi
DFR / DFR1 standard differential pressure	14 bar	approx. 203 psi
DFR / DFR1 differential pressure range	14 to 22 bar	approx. 203 to 319 psi
Zero-stroke standby pressure	approx. 1 to 2 bar above the differential setting	approx. 15 to 30 psi above
Hysteresis and repeatability	4 bar maximum	approx. 58 psi

Sizes covered by Series 31: NG 18, 28, 45, 71, 88, 100 and 140. Published characteristic curves are referenced at a drive speed of 1,500 rpm and a fluid temperature of 50 degrees C. Readings taken on a cold system will not match the data sheet.

What you need

• A calibrated pressure gauge rated well above the pump maximum, at least 400 bar or 6,000 psi.
• A gauge port at the pump outlet, port B, or a tee into the pressure line. Port X on the controller is G 1/4 in.
• Hex key for the adjustment screw and a wrench for the locknut.
• A way to load the system so pressure actually rises to the compensator setting.

Procedure, DR pressure compensator

1. Record the existing setting. Before changing anything, run the system, deadhead it against a closed function and note the pressure the gauge settles at. If you have to put it back, you will want that number.
2. Bring the fluid to operating temperature. Cold oil reads high and settles differently. The data sheet references 50 degrees C.
3. Check the system relief valve first. The pump compensator should be set below the system relief, so the pump de-strokes before the relief dumps. If the relief is set lower than the compensator, the compensator can never control and you will be chasing a fault that is not in the pump.
4. Loosen the locknut on the pressure adjustment screw. Hold the screw so it does not move as the nut breaks free.
5. Adjust with the gauge live. Clockwise increases the setting, counter-clockwise decreases it. Move in small increments, a quarter turn at a time, and let the reading stabilize between adjustments. Verify the direction on your unit from the first small movement rather than assuming it.
6. Stay inside 20 to 280 bar. The screw can be driven past this. Do not.
7. Lock it off. Hold the screw at the setting and tighten the locknut, then re-run the system and confirm the reading has not shifted. Tightening a locknut frequently moves the screw.

Procedure, DFR and DFR1 standby

On a load-sensing DFR pump, the second screw sets the differential pressure the controller maintains across the system orifice. It is what determines standby pressure when the load-sensing line is unloaded.

1. Set the DR pressure screw first, using the procedure above.
2. Unload port X to tank so the pump goes to zero stroke.
3. Read standby on the gauge. Expect roughly 1 to 2 bar, 15 to 30 psi, above the differential pressure setting, before system influences.
4. Adjust the differential pressure screw within 14 to 22 bar. The factory standard is 14 bar. Raising it increases responsiveness but also standby losses and heat.
5. Lock off and re-verify.

When adjustment is not the answer

If the pump will not hold the setting, or will not reach it at all, the controller is usually reporting a problem rather than causing one:

Symptom	Likely cause
Pressure rises then collapses under load	Worn rotary group, slipper faces, cylinder barrel or valve plate. Internal leakage is beating the control.
Setting drifts after being locked	Contamination in the control spool, or a damaged compensator spring.
High case drain flow with the pump destroked	Rotary group wear. Measure case drain against the data sheet before condemning the controller.
Noisy, foamy oil, erratic pressure	Suction-side restriction or air ingestion. Fix the inlet before adjusting anything.
Standby high on a DFR1	Load-sensing pilot line cannot unload. A valve-system issue, not a pump issue.

If any of these describe your pump, a compensator adjustment will not fix it. See our repair and rebuild service, our guide to what a rebuild actually costs, or order a Rexroth seal kit if you are doing the work in-house.

A10VSO and A10V parts by frame size

• A10VSO parts
• A10V10
• A10V18
• A10V28
• A10V45
• A10V60
• A10V63
• A10V71
• A10V74
• A10V85
• A10V100
• A10V110
• A10V140
• Rexroth seal kits

Frequently asked questions

Which way do I turn the A10VSO pressure adjustment screw?

Clockwise increases the pressure setting and counter-clockwise decreases it. Confirm the direction from the gauge on the first small movement rather than assuming, and never set by counting turns, because the valve can be driven beyond the permissible range of the pump.

What is the A10VSO pressure setting range?

On a Series 31 pump with the DR pressure controller, the setting range is 20 to 280 bar, roughly 290 to 4,060 psi, infinitely variable. The standard factory setting is 280 bar. Nominal pressure for the series is 280 bar with a maximum of 350 bar.

What should A10VSO standby pressure be?

On a DFR or DFR1 pump the zero-stroke standby pressure sits roughly 1 to 2 bar, 15 to 30 psi, above the differential pressure setting. The standard differential is 14 bar, adjustable from 14 to 22 bar.

Where is the pressure adjustment on an A10VSO?

On the controller mounted to the pump end cap. A DR pump has a single adjustment screw with a locknut. A DFR or DFR1 has two, pressure and differential pressure. Identify which control you have from position 05 of the type code before adjusting.

My A10VSO will not build pressure at all. Is it the compensator?

Sometimes, but check the cheap causes first: fluid level and suction restriction, the system relief valve setting, drive rotation direction, and whether the load-sensing line can unload. If pressure builds and then collapses under load, that usually indicates rotary group wear rather than a control fault. See hydraulic pump not building pressure.

Related guides and catalogs

• Rexroth brand hub
• A10VSO / A10VO model code decoder
• Rexroth piston pumps
• Rexroth seal kits
• Rexroth parts catalog
• Rexroth pump guide
• What a rebuild costs
• Repair and rebuild service