Gerotor Pumps: Compact Lubrication, Charge and Transfer Pumps

How a Gerotor Pump Works

The name comes from "generated rotor". An inner rotor with, say, six teeth sits inside an outer rotor with seven. The shaft drives the inner rotor, which turns the outer rotor with it, slightly off centre.

As they turn, the spaces between the teeth grow on the inlet side and pull oil in. On the outlet side, the spaces shrink and push the oil out. Because every tooth stays in contact, the flow is smooth and the pump runs quietly, with very few moving parts.

Why Gerotor Pumps Suit Lubrication and Charge Duties

• Compact: a lot of flow from a very small package, so they are easy to build into a gearbox or engine.
• Quiet and smooth: low pulsation means steady lube pressure at every bearing.
• Good suction: they prime well and cope with thick oil better than many pump types.
• Simple: only two rotors and a housing, so there is little to wear out.
• Low cost: affordable to buy, and to keep as a spare.

The trade-off is pressure. Most gerotor pumps work at low to moderate pressure, often well under 100 bar, and many lube duties run far lower than that.

Where Gerotor Pumps Work

Lubrication Systems

Gearboxes, turbines, compressors and machine tool spindles all need a steady supply of clean oil. Gerotor pumps feed that oil through filters and coolers to every bearing and gear mesh. Many sit on small motor pump sets beside the machine, while others are driven straight off a gearbox shaft. Steam and gas turbines in power generation plants rely on this kind of lube system around the clock. In these plants, a lube pump failure can trip the whole unit, which is why many sites keep a matched spare on hand.

Charge Pumps

Closed-circuit hydrostatic drives need a small pump to top up the main loop, cool it, and keep the main pump fed. A gerotor is a common choice, often built into the back of the main axial piston pump, as on the Danfoss Series 90. If the charge pump wears, the drive loses power, runs hot and can damage the main pump, so a weak charge pressure reading deserves quick attention.

Oil Transfer and Circulation

Moving oil between tanks, running a cooling loop or feeding an offline filter cart are all simple jobs a gerotor handles well. Its smooth, gentle flow suits clean oil duties where you want to avoid foaming, and its small size makes it easy to fit onto a mobile cart or skid.

Reversible Gerotor Pumps

Some gearboxes turn both ways, which can leave a standard pump pumping backwards. Reversible gerotor pumps solve this with built-in check valves or a shifting outer ring. Whichever way the shaft turns, oil still leaves through the same outlet. This is common on marine gearboxes and on industrial drives that reverse during normal work. If your machine changes direction, check whether the old pump was reversible before you order.

Gerotor Pump or Gerotor Motor?

Orbital motors use the same rotor idea to turn oil flow into slow, high torque rotation for augers, conveyors and wheel drives. A motor will not work as a pump, and the parts are not interchangeable. If you actually need an orbital motor, our hydraulic motors range covers them.

Choosing the Right Gerotor Pump

Before you order, confirm these points:

1. Displacement, or flow at your shaft speed.
2. Working pressure, including any built-in relief valve setting.
3. Drive style: shaft-mounted, foot-mounted, or motor-pump set.
4. Rotation, or whether you need a reversible design.
5. Oil type and viscosity, especially the cold start viscosity.
6. Ports and mounting details.

Cold starts catch many people out. Thick oil on a winter morning can overload a small motor or starve the pump, so size the drive for the coldest conditions you expect. If you want a second opinion, our pump selection and sizing team can check the numbers.

Keeping a Lube System Healthy

A gerotor pump is only as good as the system around it. Keep these basics in check:

• Clean oil: change the filters on schedule, as worn rotor tips cut lube pressure quickly.
• Right temperature: a working oil cooler keeps viscosity in range and protects bearings.
• Good suction: keep strainers clear and the suction line short.
• Pressure monitoring: a gauge or switch on the lube line warns you before bearings suffer.

A slow fall in lube pressure over weeks usually means internal wear. A sudden drop points to a blocked strainer or a failed drive.

Gerotor, External Gear or Internal Gear?

Gerotor pumps are the specialists for low-pressure lubrication and charge work. For higher pressure mobile and general duties, external gear pumps offer more force for the money. For quiet, high-pressure indoor machines, internal gear pumps are the better pick.

Why Buy From TSA Hydraulics Engineering

As a gerotor pump supplier, we know lube and charge pumps rarely arrive with clear labels or full paperwork. Our engineers work from part numbers, photos and measurements to find the right match, and we tell you upfront whether it is genuine or an equivalent. You get clear prices in AUD and help sourcing generator pump replacement parts such as rotor sets and seal kits.