Gear Pumps - Internal

Smooth, Quiet and Precise

Internal gear pumps are a popular choice for hydraulic systems requiring quiet operation, high efficiency, and precise flow control. Known for their compact design and excellent suction capabilities, these pumps are ideal for handling a wide range of fluids – including those with higher viscosities.

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Internal gear pump. For impartial advice and access to our full range of hydraulic components, contact our expert team.

Invented by Jens Nielsen in the early 20th century, internal gear pumps use a clever offset gear arrangement to deliver smooth, continuous flow. Here’s how they operate:

A rotor (external gear) meshes with an idler (internal gear) inside a crescent-shaped cavity.
As the gears rotate, fluid is drawn into the expanding cavities on the inlet side.
The fluid travels around the pump casing and is compressed as the gears re-mesh on the outlet side.
The crescent-shaped partition separates the inlet and outlet, preventing backflow and ensuring consistent pressure.

This design allows internal gear pumps to deliver low-pulsation flow, making them ideal for applications where noise, vibration, and precision matter.

Most are not reversible due to their asymmetric design and the fixed position of the crescent partition. However, some specialised models offer bidirectional flow capabilities – typically with modified internal geometries.

If you need a reversible pump, our team can help identify the right solution based on your system’s requirements.

Yes. Internal gear pumps are among the quietest hydraulic pump types available. Their smooth gear engagement and low-pressure ripple make them ideal for noise-sensitive environments. Key design features include:

Internal gear geometry for smoother fluid movement
Tight tolerances that reduce vibration
Low operating speeds that minimise mechanical noise

These attributes make these pumps a top choice for precision machinery, laboratory equipment, and mobile hydraulic systems.

If you’re comparing hydraulic pump types or designing a new system, check out our Hydraulic Pumps Ultimate Guide covering:

Internal versus external gear pumps
Vane, piston, and screw pump comparisons
Ideal applications for each pump type
Tips for selecting the right pump for your system

Whether you’re an engineer, technician, or procurement specialist, this guide is packed with insights to help you make informed decisions.

Why choose an internal gear pump over an external gear pump? Internal gear pumps excel when you need smooth, pulse‑free flow and strong suction performance, especially with thicker or temperature‑sensitive fluids. They’re also better suited to applications where noise reduction and precise metering matter, whereas external gear pumps are typically chosen for simpler, higher‑speed, lower‑cost systems.

How do internal gear pumps perform with different fluid types? Their design makes them highly tolerant of a wide viscosity range, from thin hydraulic oils to heavy lubricants and polymers. This versatility is why they’re often used in chemical processing, lubrication circuits, and fluid transfer tasks where other pump types may struggle with cavitation or inconsistent flow.

What factors influence the service life of an internal gear pump? Longevity is shaped by fluid cleanliness, operating temperature, system pressure, and how well the pump is matched to the application. When correctly specified, internal gear pumps offer excellent durability thanks to their low internal stress and gentle pumping action. If you’re unsure about sizing or compatibility, our team can help you avoid premature wear.