Rexroth A10VSO and A10VO Pump Troubleshooting

When a Rexroth A10VSO or A10VO will not make pressure, gets loud, runs hot or hunts, the cause is usually outside the pump: air or a starved inlet, a case drain that is pressurizing the housing, a relief valve set below the compensator, or a load-sense line that cannot unload. Check those against Rexroth's own limits below before you touch the controller or pull the pump, and if the inlet, case and settings are all right and it still will not hold pressure, the rotating group is worn.

The figures here come from Bosch Rexroth's data sheets for Series 31, 32 and 52/53 and the Series 52/53 instruction manual. Where Rexroth does not publish a number, we say so.

Three gauges before any wrench. Rexroth's own commissioning instructions call for gauges on working pressure, case pressure and suction pressure. Working pressure at port B, case pressure at port L or L1, suction at port S. With those three readings most A10 faults name themselves.

What limits is the pump supposed to run within?

These are the figures you are checking your gauges against. Note that Rexroth gives inlet and case pressure as absolute, not gauge.

Limit	A10VSO Series 31 (RE 92711)	A10VSO Series 32 (RE 92714)	A10VO Series 52/53 (RE 92703)
Nominal / maximum pressure	280 / 350 bar	280 / 350 bar	250 / 315 bar
DR pressure setting range	20-280 bar	20-280 bar	35-250 bar
Minimum inlet pressure at S	0.8 bar absolute	0.8 bar absolute (1.0 high-speed)	0.8 bar absolute
Maximum inlet pressure at S	10 bar	10 bar absolute	5 bar absolute
Maximum case pressure at L / L1	2 bar absolute, and never more than 0.5 bar above the inlet pressure at S. A drain line back to the reservoir is required.
Fluid temperature at the drain port	Up to 110 °C with FKM (Viton) seals, 85 °C with NBR	-25 to +85 °C, and no point on the pump above 90 °C	-25 to +110 °C, and no point on the pump above 115 °C
Optimum viscosity	16-36 mm²/s
Cleanliness	At least 20/18/15 to ISO 4406, tightened to 19/17/14 at very high fluid temperatures

What absolute means on your gauge: at sea level a gauge reads about 1 bar below absolute. So 0.8 bar absolute at the inlet is roughly 0.2 bar (about 6 inHg) of vacuum, and 2 bar absolute in the case is roughly 1 bar, or about 15 psi, on the gauge. The 0.5 bar rule is usually the tighter one. With a flooded inlet sitting near zero on the gauge, the case should not read more than about 0.5 bar, or 7 psi.

A10VSO troubleshooting: symptom, cause, check, fix

This follows the malfunction table in Rexroth's instruction manual RE 92703-01-B, with the checks we make in the shop. Rexroth's first advice is worth repeating: find out what changed before the fault appeared, and do not turn screws at random, because that destroys the evidence.

Symptom	Likely causes	Check	Fix
No flow	Case and suction line not filled or bled. Failed coupling. Wrong rotation. Drive speed too low. Suction blocked or a shut-off valve closed.	Bubbles at the drain line. Rotation against the nameplate arrow. The coupling.	Fill the case through the highest drain port and bleed it. Open every shut-off valve. Correct rotation or coupling.
Low pressure, or will not build pressure	System relief set below the compensator. DR screw set low. On a DFR, the load-sense line at X is open, broken or unloaded, so the pump sits at standby. On a DRG, the remote relief valve on X is set low or leaking. Starved inlet. Control spool stuck with dirt. Worn rotating group. A worn motor or cylinder downstream.	Pressure at port B deadheaded, against the relief setting. Standby with X unloaded. Suction and case pressure.	Set the relief above the compensator. Restore the load-sense signal. Clean the control. Pressure that builds then collapses under load, with good inlet and case readings, means a worn rotating group.
Pressure or flow unstable, hunting	Air in the system. Poor suction. Controller and system relief fighting each other because they are set too close. Unstable electrical control signal on ED or ER. Remote line on a DRG too long. Contamination on the control spool.	Foamy oil, suction reading, relief vs compensator gap, X line length, control current.	Fix the inlet first. Separate the relief and compensator settings. Keep DRG remote piping within Rexroth's 2 m. Clean or replace the control valve.
Noise	Air. Suction line too small, oil too thick, suction height too great, a filter in the suction line, debris in the suction line. Drive speed too high. Wrong rotation. Bad mounting or coupling. Controller vibrating. Bearing damage.	Suction pressure at nominal speed and full stroke. Oil grade and temperature. Coupling and alignment.	Fix the suction side. Correct speed, rotation and mounting. Bearings mean a teardown.
Overheating	Hot oil reaching the inlet: failed cooler, low reservoir, return oil drawn straight back into the suction. Relief or pressure cut-off set wrong, so oil is dumping over a valve. Standby set high on a DFR. Worn pump.	Temperature at the drain port and in the reservoir. Whether the relief passes oil with the pump destroked. Standby pressure.	Fix cooling and reservoir layout. Set the compensator below the relief. Bring standby back toward the factory setting. A hot pump with good settings is a rebuild.
Leaking at the shaft seal	Case pressure above the limit: drain line too small, shared with another unit, fitted with a check valve, or plumbed into a pressurized return. Overheated seal. A pressure washer aimed at the seal.	A gauge in the case drain at maximum working pressure.	Fix the drain plumbing first. Then the seal. See pump leaking from the shaft.
Control not responding, stuck at full or zero stroke	Control spool stuck by contamination. Insufficient pilot or control pressure. On a DFR1, the X line has no unloading path in the valve system. On ED or ER, wrong or missing solenoid current.	Pilot pressure at X. Current at the solenoid. Whether the valve system can vent the load-sense line.	Clean or replace the control valve and find the dirt source. Give the DFR1 X line a way to unload. Fix the electrical supply.

The compensator is not a relief valve. Rexroth says it plainly in every one of these data sheets: pressure controllers are not protection against overpressure, and the system needs its own relief valve. The relief belongs above the compensator setting. Set it below and the relief dumps oil all day, the pump never controls, and the oil cooks.

DR, DRG, DFR, DFR1 or LA: which control do you have?

The control code sits right after the frame size in the type code: A10VO71DFR/31L-PSC12K68. Read it before you touch a screw. Series 32 and the 52/53 data sheets also write the flow controllers as DRF and DRS, which are the same thing as DFR and DFR1.

Code	What it does	What you can adjust	Factory figures
DR	Pressure controller. Destrokes the pump at the set pressure.	One screw: pressure.	Series 31 and 32: 20-280 bar, 280 bar standard. Series 52/53: 35-250 bar, 250 bar standard.
DRG	DR plus a remote relief valve on port X, to set pressure anywhere below the DR setting.	Pressure screw, the differential pressure, and the external relief valve (not supplied with the pump).	Differential 10-22 bar, 20 bar standard. Remote piping no longer than 2 m.
DFR (DRF)	Pressure and flow (load-sense) controller. Holds a set pressure drop across an orifice or valve, so the pump delivers only the flow the load needs. X to tank open.	Two screws: pressure, and differential pressure (standby).	Differential 14 bar standard, adjustable 14-22 bar on Series 31 and 52/53, 10-22 bar on Series 32. Standby with X unloaded runs about 1-2 bar above the differential.
DFR1 (DRS)	As DFR, but X to tank is plugged, with a flushing function.	As DFR.	As DFR. The load-sense line must be able to unload through the valve system.
DFLR (Series 31), LA (Series 32, 52/53)	Pressure, flow and power control. Holds flow times pressure constant, capping input power.	Pressure and flow as above. The power curve is set at the factory to the order, for example 20 kW at 1500 rpm.	The LA5 to LA9 suffix gives the pressure at which power control begins, and the bands differ between Series 32 and 52/53.
ED / ER	Electrohydraulic pressure control set by solenoid current.	Current, plus a hydraulic pressure cut-off.	ED goes to maximum pressure as current falls to zero, by design, as a fail-safe for fan drives. ER drops to standby at zero current. Too much current on an ER (over 1200 mA at 12 V, 600 mA at 24 V) can overpressure the system, so Rexroth calls for a current limiter.

For the setting procedure itself, use our A10VSO pressure compensator adjustment guide: gauge first, oil at temperature, relief checked, small moves, lock it off and re-read.

On older controllers, Rexroth's 1989 A10VO / A10VSO operating instructions (RE 92701-B) put the pressure screw under a cap nut, with a 4 mm hex socket and a 17 mm locknut, and the flow screw behind a 13 mm cap nut with a 3 mm hex socket. Clockwise raised both. On the horsepower valve, screw 1 set where power control begins and screw 2 the cut-off. Current controllers can differ, so confirm on yours.

A10VSO case drain pressure: why it matters and what to check

The case is supposed to sit at nearly tank pressure. Every A10 data sheet here caps it at 2 bar absolute and no more than 0.5 bar above the inlet pressure. Go past that and the first thing to give up is the shaft seal.

Drain from the highest port, L or L1, so the case stays full.
One drain per pump if in doubt. A shared drain must keep every connected unit under its case limit in all conditions, cold start included. If it cannot, run separate lines. Combination pumps need a drain from each pump.
No check valve in the drain unless Rexroth has approved it for the installation.
Below the oil. Suction and drain lines both end below the minimum fluid level, far enough apart that hot drain oil is not pulled straight back into the suction.
Read it under load. Rexroth's commissioning check is case pressure at maximum working pressure, not at idle.

Some leakage to the case is normal, and the controller itself uses pilot oil: RE 92711 puts its consumption at roughly 3 l/min for a DR and up to about 5.5 l/min for a DFLR. The data sheets publish no wear limit for case drain flow, so compare against a known-good pump or your own records. Rising case flow on the same machine is the trend that matters.

Inlet conditions: the cause behind most noise

0.8 bar absolute minimum at port S, in operation and at cold start. Rexroth sets that floor to keep the pump from cavitating and damaging itself.
Suction height no more than 800 mm (Series 31 and 32), with the suction pipe at least 200 mm under the oil and 100 mm off the reservoir bottom.
No filter in the suction line unless it is one the system was designed for. Rexroth lists an impermissible suction filter as a cause of noise, no flow and no pressure.
Cold start: on Series 31, viscosity no higher than 1600 mm²/s, for no more than 3 minutes, unloaded (50 bar or less) and at 1000 rpm or less.
Above-reservoir installs are the noisy, risky ones. After a long standstill the case can drain down, with air getting in past the shaft seal, and the bearings start dry. Rexroth's instruction manual says such a pump must reach full swivel angle within three seconds at start-up and actually pull in oil and build pressure.

Side loads kill bearings too. RE 92711 does not permit pinion or V-belt drives on Series 31, and the Series 32 and 52/53 sheets say to ask Rexroth first.

Series 31 vs 32 vs 52/53: what actually differs

Series	Data sheet	Sizes	What the factory sheet points out
A10VSO 31	RE 92711	18-140	280 bar nominal, 350 bar max. Controls DG, DR, DRG, DFR, DFR1, DFLR, ED, ER. Two drain ports.
A10VO 31	RE 92701	28-140 (size 18 as A10VSO)	Same pressure ratings and control family as the A10VSO 31.
A10VSO 32	RE 92714	45-180	280 bar nominal, 350 bar max. Hydrostatic unloading of the cradle bearings, a sensor port on the high-pressure port, and higher resistance to cavitation, loss of suction pressure and case pressure peaks. LA power control. Lowest temperature ceiling of the three.
A10VO 52/53	RE 92703	10-100	250 bar nominal, 315 bar max. DR range 35-250 bar. Inlet limit 5 bar absolute. Adds EP electro-proportional controls. The ordering code is written A10V(S)O, so it covers A10VSO 52/53 as well.

The series is the number after the slash in the type code, and internal parts do not cross between generations even on the same frame size. Our A10VSO / A10VO model code decoder reads the rest of the code.

Starting up a rebuilt or replacement A10 pump

This is Rexroth's commissioning sequence from RE 92703-01-B, in the order we run it. Skip it and a fresh rebuild can be damaged in its first minute.

Fill and bleed. Fill the case through the drain port and fill the suction line, using filtered oil. New oil out of the drum is usually not clean enough for these pumps.
Open every shut-off valve in the suction and drain lines before the drive can start.
Check rotation by inching the drive at the lowest speed and comparing to the arrow on the nameplate.
Run at low speed until the drain oil is free of bubbles. The 1989 instructions add that if it is not delivering bubble-free after about 60 seconds, recheck the system.
Run unloaded, listening for noise and watching for leaks, then add load and confirm working pressure rises as it should.
Read suction pressure at nominal speed and full stroke, and case pressure at maximum working pressure, against the limits above.
Watch temperature through running-in. Rexroth puts running-in at about 10 operating hours, then recommends an oil sample, and an oil change if the sample fails or is not taken.

When it is the pump, not the system

If inlet and case read right, the relief sits above the compensator and the control is clean, and the pump still will not hold pressure or keeps getting louder, it is worn. Rexroth ties service life to the bearings and reads increased vibration as worn bearings.

A leak on its own, with good pressure and a clean case reading, is usually a seal kit job. Anything involving pressure loss, heat with good settings, or bearing noise is a teardown. Our repair and rebuild service starts with a free teardown evaluation and a firm itemized quote before any billable work, and repair work carries a 1-year warranty. Doing it yourself? See Rexroth seal kits, the A10VSO parts catalog and the Rexroth rebuild guide.

Frequently asked questions

Why is my A10VSO not building pressure?

Check the cheap causes first: a system relief set below the compensator, a low DR setting, a broken or unloaded load-sense line on a DFR (the pump then sits at standby), a starved inlet and wrong rotation. Pressure that builds then collapses under load, with good suction and case readings, means a worn rotating group.

What is the maximum case drain pressure on an A10VSO?

Rexroth gives 2 bar absolute at port L or L1 for Series 31, 32 and 52/53, and never more than 0.5 bar above the inlet pressure at port S. With a flooded inlet, that is roughly 0.5 bar (7 psi) on a gauge.

Why is my Rexroth A10VSO noisy?

Usually the suction side: air, a suction line too small, oil too thick, too much suction height or a filter in the suction line. Rexroth also lists overspeed, wrong rotation, poor mounting, a vibrating controller and bearing damage. Check suction against the 0.8 bar absolute minimum first.

Why is my Rexroth pump overheating?

Usually hot oil reaching the inlet from a failed cooler or low reservoir, or oil dumping over a relief set below the compensator. High DFR standby adds heat too. If cooling and settings are right and it still runs hot, the pump is worn.

Why is A10VSO pressure unstable or hunting?

Air or poor suction, a controller and relief set too close together, an unstable ED or ER control signal, a DRG remote line longer than Rexroth's 2 m limit, or dirt on the control spool. Fix the inlet before adjusting anything.

What should A10VSO standby pressure be?

On a DFR or DFR1 the standard differential is 14 bar, adjustable 14 to 22 bar on Series 31 and 52/53 (10 to 22 bar on Series 32). Standby with port X unloaded runs about 1 to 2 bar above the differential.

About the technical information on this page. Figures, procedures and part numbers here come from manufacturer service literature and are provided for reference only. They are only as accurate as the factory data, and the revision we have on file may not be the latest for your unit. Always confirm against the current manufacturer documentation for your exact model and follow safe work practices. RestoPower is not responsible for damage, injury or loss resulting from the use or misuse of this information, or from incorrect assembly, adjustment, installation or operation of any unit.

Send the type code and your three gauge readings

Give us the full code off the nameplate, working pressure, case pressure and suction pressure, and what changed before the fault started. That usually tells us whether you need a setting, a seal kit or a rebuild. We reply with price, availability and lead time.

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