Internal gear pumps
They are suitable for systems that require very high working pressures. They are primarily used in die casting, plastic and rubber injection machine tools, and hydraulic power units sectors.
Thanks to special design features and effective force balancing, they ensure high volumetric efficiency and a significant reduction in noise emissions.
They are ideal for applications with a servo pump and allow for considerable energy savings.
Available internal gear pumps
| Brand | Series | Working pressure (bar) | Link |
|---|---|---|---|
 | QX | 400 | Read more |
| QXEH - QXEHX | 280 | Read more |
| QXM - QXEM | 400 - 250 | Read more |
 | HIGP1 - HIGP21 - HIGP42 | 315 | Read more |
What is an internal gear pump and how does it work
An internal gear pump is a positive displacement pump in which a small external gear (the pinion), driven by the shaft, meshes with a larger ring gear with internal teeth. A crescent-shaped filler piece separates the suction side from the delivery side: as the teeth disengage, oil is drawn in; as they re-engage, it is pushed towards the outlet at a constant volume per revolution.
Modern internal gear pumps use radial and axial compensation: the delivery pressure itself presses the sealing elements against the gears, reducing internal leakage. The result is high volumetric efficiency that stays constant as pressure varies, very low pressure and flow pulsations and low noise, with continuous pressures above 300 bar on the most advanced series.
Internal vs external gear pumps
| Internal gear pump | External gear pump | |
|---|---|---|
| Working pressure | High: up to 400 bar intermittent (Bucher QX) | Medium: typically 150–200 bar |
| Noise and pulsation | Very low, below 75 dB(A) on Bucher QX | Higher |
| Volumetric efficiency | High and stable as pressure varies | Good, decreases at high pressure |
| Variable speed / servo pump | Ideal, several series designed for it | Limited |
| Cost | Higher | Lower |
| Typical uses | Injection moulding, die casting, presses, machine tools, power units | Mobile hydraulics, agricultural machinery, simple power units |
Internal gear pumps for servo pump drives
In a servo pump system the pump is driven by a variable speed motor that delivers only the flow the machine needs at each moment, instead of running at constant speed and wasting energy through relief valves. Internal gear pumps are the reference technology for these systems because they keep their efficiency even at low speed, tolerate reversals and fast speed changes and stay quiet. The energy savings compared with a constant speed pump are significant, especially on machines with long holding phases such as injection moulding machines and presses.
Internal gear pump series available from Interfluid
| Series | Function | Continuous / max pressure (bar) | Displacement (cm³/rev) | Max speed (rpm) |
|---|---|---|---|---|
| Bucher QX | Fixed or variable speed pump | 320–360 / 400 | 3–450 | 3,600 |
| Bucher QXM | Pump/motor, four quadrants | 320 / 400 | 5–500 | 4,000 pump / 6,000 motor |
| Bucher QXEH | Variable speed with reversal | 250 / 280 | 10–250 | 5,500 |
| Bucher QXEHX | High dynamics, very high speed | 210–250 / 250–280 | 10–160 | 6,050 |
| Bucher QXEM | Pump/motor, multi-quadrant | 210 / 250 | 5–250 | 3,250 pump / 6,000 motor |
| Hydraut HIGP | Fixed displacement, single and double | max 315 | 4–180 | 3,000 |
How to choose an internal gear pump
- Pressure: continuous and peak pressure of the circuit. Above 300 bar continuous, Bucher QX and QXM.
- Drive: fixed speed motor or servo drive; for highly dynamic variable speed and reversal, QXEH, QXEHX or QXEM.
- Displacement and speed: the flow required at the operating speed.
- Fluid: mineral oil or fire resistant and biodegradable fluids (Hydraut HIGP works with HLP, HFC, HEES and HFD-U).
- Multiple pumps: double and multiple combinations with common or separate inlet.
- Budget and availability: Hydraut HIGP is a cost-effective alternative to Voith, Bucher, Eckerle and Rexroth internal gear pumps, with stock availability.
Internal gear pump FAQ
What is the difference between internal and external gear pumps?
Internal gear pumps reach higher pressures (up to 400 bar), are quieter and keep a stable efficiency as pressure varies, which makes them ideal for servo pumps. External gear pumps are simpler and cheaper and are used at medium pressures, mainly in mobile hydraulics.
What is the maximum pressure of an internal gear pump?
Up to 400 bar intermittent and 320–360 bar continuous with the Bucher QX series; up to 315 bar with Hydraut HIGP.
Can internal gear pumps be used with variable speed drives?
Yes. Bucher QXEH, QXEHX and QXEM are designed for variable speed and reversal, up to 6,050 rpm on QXEHX.
Is there an alternative to Rexroth, Voith or Eckerle internal gear pumps?
Yes: Hydraut HIGP internal gear pumps are an alternative to Voith, Bucher, Eckerle and Rexroth. Send us the code of the pump you use and we will propose the equivalent.
Why choose Interfluid
- Official Bucher Hydraulics distributor and Hydraut brand owner
- Stock of the most requested series: Bucher QX2 to QX8, QXEH and QXEHX; Hydraut HIGP1, HIGP21 and HIGP42
- Technical support for servo pump sizing and pump replacement
- Online ordering on Fluid-Hub.net
Tell us the pump code you use today or the pressure, flow and drive of your application – request a free consultation.
To learn more
Internal gear pumps: construction technology, operation and advantages
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