We repair Danfoss and Sauer-Danfoss hydrostatic pumps and motors, including Series 90, H1 and Series 45 pumps, and the Danfoss orbital motors (OMP, OMR, OMS, OMT, OMV and similar) that drive winches, capstans, conveyors and many smaller deck and plant machines. We are an independent repairer, not a Danfoss authorised service partner.
A quick note on names
Danfoss and Sauer-Sundstrand merged in 2000 to form Sauer-Danfoss, which later became Danfoss Power Solutions. Equipment built in the 2000s often carries the Sauer-Danfoss name on the plate, while older units may say Sauer-Sundstrand. They are the same product lines. Danfoss also took over Eaton’s hydraulics business, so some Vickers and Char-Lynn products now sit in the same group.
The units we see most
| Unit | What it is | Typical use |
|---|---|---|
| Series 90 pumps and motors | Closed circuit axial piston, variable pump, fixed or variable motor | Hydrostatic drives on winches, drill rigs and mobile machines |
| H1 pumps and motors | Newer closed circuit family, often electronically controlled | Mobile machines, newer winch drives |
| Series 45 / Series 40 | Open circuit and smaller closed circuit pumps | Mobile plant, auxiliary drives |
| Orbital motors (OMP, OMR, OMS, OMT, OMV) | Low-speed high-torque gerotor motors | Capstans, small winches, conveyors, slewing drives, augers |
| Steering units (OSPC and similar) | Hydrostatic steering control units | Mobile machines, some marine steering |
How a closed circuit drive works
In a Series 90 or H1 system the pump and motor form a loop. The pump’s swashplate angle sets both direction and speed. A charge pump on the main pump keeps the loop topped up and cool, through check valves, while a loop flushing valve on the motor takes some hot oil out to the cooler. Multifunction or high pressure relief valves protect the loop.
This means many “pump failures” are actually problems in the support systems: low charge pressure, a blocked charge filter, a stuck flushing valve or a weak relief valve.
Typical failure modes
Series 90 and H1 pumps and motors
- Loss of drive in one or both directions, from low charge pressure or a faulty control.
- Slipper, swashplate and valve plate wear from contamination or heat.
- Overheating, often from a blocked cooler, a loop flushing problem or worn rotating groups leaking internally.
- Servo piston or control faults causing sluggish or uneven response.
- Shaft seal leaks from high case pressure.
Orbital motors
- Shaft seal leaks, usually caused by back pressure or case pressure above the motor’s rating. A drain line may be needed.
- Wear of the gerotor set and distributor valve, showing as loss of speed or torque under load.
- Shaft and bearing wear from side loads, for example from a chain or belt drive tensioned too hard.
In UAE conditions, closed loops in particular suffer when the cooler is undersized or clogged with dust, because the loop oil only cools through the flushing flow. See hydraulic overheating in UAE heat.
Checks before removal
- Charge pressure at idle and at working speed.
- Loop pressures in both directions with gauges.
- Case drain flow where accessible.
- Charge filter condition and oil temperature.
- For orbital motors: back pressure in the return and drain lines.
We often find a charge, filter or control fault that does not need the pump removed at all.
What to read off the nameplate
Danfoss and Sauer-Danfoss plates carry:
- Model code, a long string identifying the series, size, control and options (for example a Series 90 code beginning 90R or 90L with the size such as 055 or 075).
- Model number, a short number for ordering.
- Serial number, which also gives the build date.
For orbital motors, the type (OMP, OMR, OMS and so on), displacement in cc/rev and the code number on the label are enough. If the plate is missing, send photographs of the shaft, flange and ports and the machine it came from.
How we repair
- Strip and inspect the rotating group, valve plate, swashplate, charge pump, control and valves, and measure the wear.
- Report and quote, with photographs and the parts needed.
- Rebuild with genuine or equivalent parts, stated in the quote, and set the control and charge relief to specification.
- Test before return.
Orbital motors are often more economical to replace than repair, especially smaller sizes. We tell you honestly which is cheaper.
Repair or exchange
For Series 90 and H1 units the housings are robust and repair is usually good value. Exchange is worth considering if the housing or end cap is cracked, the shaft spline is worn or the unit is an obsolete variant. For small orbital motors, new is often the better option; for large OMT and OMV motors, repair is usually worthwhile.
