Popular Hydraulic Pump & Motor Questions, Answered
The questions below are the ones equipment owners, mechanics, and buyers search most about hydraulic pumps, motors, and valves. Each answer is short, straight, and links to the parts, seal kits, or guides you need next. Can't find yours? Send us photos and any numbers and a specialist will help.
Hydraulic pump & motor basics
What is the difference between a hydraulic pump and a hydraulic motor?
A hydraulic pump converts mechanical energy (from an engine or electric motor) into fluid flow. A hydraulic motor does the reverse — it converts hydraulic flow and pressure back into rotary mechanical motion to drive a wheel, winch, or fan. Many pumps and motors look alike on the outside, but their internal porting and bearings differ.
What are the three main types of hydraulic pumps?
| Type | Best for | Common series we support |
|---|---|---|
| Gear | Simple, economical, fixed flow, lower pressure. | Gear pumps & PTO units |
| Vane | Quiet, medium pressure, fixed or pressure-compensated. | Vickers V10, V20, 25V/35V/45V, VQ |
| Piston | Highest pressure and efficiency; fixed or variable displacement. | Vickers PVH, PVB, PVQ, PVM, Rexroth A10VSO |
How does a hydraulic pump work?
A pump creates flow, not pressure. As it turns, it opens an expanding volume at the inlet that draws fluid in, then a shrinking volume at the outlet that pushes fluid out. Pressure only builds when that flow meets resistance in the system — a cylinder under load, a closed valve, or an orifice.
What is the difference between a vane pump and a piston pump?
Vane pumps have a round or oval cartridge body, often a square mounting flange, and run quietly at medium pressure. Piston pumps are longer and barrel-shaped, usually with a pressure-compensator adjustment on the end cap, and handle much higher pressure. Our full walkthrough is here: How to identify a Vickers hydraulic pump.
What does fixed vs. variable displacement mean?
Fixed displacement pumps move the same volume every revolution (most gear and vane pumps). Variable displacement pumps — typically piston pumps with a compensator — adjust their output to match demand, which saves energy and runs cooler.
What is a pressure compensator?
On a variable piston pump, the pressure compensator automatically de-strokes the pump when system pressure reaches its setting. That caps maximum pressure, reduces wasted horsepower, and keeps the oil from overheating.
What does tandem, double, or thru-drive pump mean?
All three use one input shaft to drive more than one pumping section. A double or tandem pump feeds two separate circuits; a thru-drive passes power straight through to a second pump mounted behind the first. Vickers examples include V2010 and V2020 doubles.
Troubleshooting & failure
How do I know if my hydraulic pump is bad?
Common symptoms: unusual noise (whining or knocking), overheating, slow or weak operation, loss of pressure or flow, external leaks, and milky or foamy fluid. Metal particles in the oil or filter are a sign of internal wear. If you catch it early, a seal kit or rebuild often saves the pump.
Why is my hydraulic pump noisy or whining?
Almost always cavitation (a starved inlet) or aeration (air getting in). Check for a clogged suction filter, low fluid, a closed suction valve, cold or too-thick oil, a loose inlet fitting, or a worn shaft seal. Running a noisy pump destroys it quickly, so fix the cause first.
What is cavitation in a hydraulic pump?
When inlet pressure drops too low, vapor bubbles form in the fluid, then collapse violently on the pressure side. That implosion erodes the internal parts. It's caused by restricted or undersized suction lines, low oil level, a dirty filter, or cold, thick oil at start-up.
What causes a hydraulic pump to fail?
In order: contamination (dirt and water — the number-one cause), cavitation and aeration, low fluid, over-pressurization, the wrong or degraded fluid, worn seals, and shaft misalignment. Clean oil and the right filter prevent most failures.
Why is my hydraulic system overheating?
Heat comes from wasted energy: internal leakage in a worn pump, a relief valve stuck or set too low, low or dirty fluid, a plugged cooler, or a compensator not de-stroking. Persistent heat degrades the oil and seals, so it's worth diagnosing promptly.
Repair, seals & rebuild
Can a hydraulic pump be rebuilt or repaired?
Yes. Most vane and piston pumps are designed to be rebuilt with a seal kit and replacement wear parts — cartridge, rotating group, valve plate, bearings — for a fraction of the price of new. Browse used, reman & core parts or the Eaton / Vickers parts hub to source what you need.
What is a hydraulic seal kit?
A seal kit is the matched set of O-rings, the shaft seal, and gaskets needed to reseal a pump, motor, or valve. Replacing the seals fixes most external leaks and is the first step in any rebuild. We stock hydraulic seal kits in both standard Nitrile/Buna and high-temperature Viton FKM.
How do I identify my hydraulic pump?
Work from type → family → model code. Determine whether it's vane, piston, or gear; match the physical features to a family; then decode any surviving nameplate characters. Full guide: How to identify a Vickers hydraulic pump.
How long does a hydraulic pump last?
With clean fluid and proper maintenance, many industrial pumps run well past 10,000 hours. Contamination, cavitation, and running low on oil are what cut that life short.
What hydraulic fluid should I use?
Follow the equipment maker's specification — usually an anti-wear hydraulic oil (AW 32, 46, or 68) matched to your operating temperature. Don't mix incompatible fluids, and keep it clean; contamination causes more pump failures than anything else.
Buying, brands & new old stock
What hydraulic brands does RestoPower carry?
We specialize in Eaton Vickers, plus Char-Lynn / Eaton orbital motors, Denison, Parker Hannifin, Bosch Rexroth, Oilgear, Sundstrand, and Poclain. See the full products & catalogs list.
What is new old stock (NOS)?
New old stock is a genuine part that was manufactured but never used — often an obsolete or discontinued item still in its original box. NOS parts are prized for keeping legacy equipment running when the maker no longer supplies them.
Does RestoPower buy surplus or new old stock hydraulics?
Yes — we pay cash for it. Sell your Vickers surplus on our We Buy NOS Vickers page, or any brand on We Buy New Old Stock Hydraulics. Email your list to info@restopower.com for a quick quote.