Internal Gear Pumps: The Silent Guardian of Precision Fluid Transmission

As a representative positive-displacement pump, the internal gear pump stands out with its compact structure, low pulsation and superior viscosity tolerance. We break down five real-world cases—plastics, lubrication, chemical dosing, marine and food—where switching to internal-gear technology cut downtime and energy bills.

1. Plastics: Hydraulic Power Units for Injection Moulding Machines

Injection moulding machines require differentiated pressure and flow across clamping, injection, holding, cooling and mould-opening phases. When conventional fixed or variable displacement pumps run with asynchronous motors, flow continues during holding and cooling phases, with excess oil returning to the tank through the relief valve and energy lost as heat.

Internal gear pumps offer two technical advantages here. First, low flow pulsation. The internal gear meshing action produces smoother output than external gear designs, which helps reduce pressure fluctuation during holding pressure and improves part repeatability. Second, high volumetric efficiency at low speed. When the machine enters cooling and the servo motor speed drops to near standstill, the internal gear pump maintains stable volumetric efficiency rather than suffering increased internal leakage as speed falls. This makes it highly compatible with servo drive systems and a key component in achieving oil-on-demand and speed-on-demand control.

Selection considerations include whether the rated pressure covers the machine's maximum working pressure, whether displacement matches peak flow demand during the moulding cycle, and whether the shaft specification is compatible with the servo motor output shaft.

2. Lubrication: High-Viscosity Oil Delivery

In central lubrication systems, gearbox lubrication and large bearing lubrication, oil viscosity is often high, and fluidity drops markedly during cold starts. External gear pumps suffer significant pressure loss in the suction chamber when drawing high-viscosity oil, leading to cavitation, noise, vibration and premature seal failure.

The internal gear pump's suction principle gives it a natural advantage in this duty. Its larger inter-tooth volumes and favourable suction chamber geometry help high-viscosity oil fill efficiently with relatively low suction resistance. The internal gear pump also tolerates a wider viscosity range, maintaining stable output from cold high-viscosity starts through to high-temperature low-viscosity operation.

Selection requires confirming that suction port dimensions and suction path design suit high-viscosity oil, and whether larger suction piping or forced-feed supply is needed. Where self-priming is required, verify that suction height and inlet vacuum fall within the pump's allowable range.

3. Chemical Dosing: Shear-Sensitive Media Injection

Water treatment flocculants, polymer solutions and certain food additives are shear-sensitive and prone to molecular chain scission, floc structure damage or viscosity change under high shear. Traditional metering pumps such as progressive cavity or diaphragm pumps may affect downstream process stability through internal shear or pulsating output.

The internal gear pump's internal flow path is relatively smooth, and shear action during gear meshing is mild, making it suitable for shear-sensitive media. As a positive-displacement pump, its output flow is linear with rotational speed, enabling stable metered dosing when combined with variable-frequency drive, with lower output pulsation than plunger pumps and many screw pump designs.

Selection considerations include whether pump body and seal materials are compatible with the medium, whether a heating jacket is required, and whether the speed range covers the required dosing band. For precise dosing duties, prioritise pump types with stable volumetric efficiency and controllable internal leakage.

4. Marine: Fuel Oil and Lubricating Oil Transfer

Engine room space is limited, installation and maintenance conditions are constrained, and pumps must meet demanding requirements for size, weight and reliability. In fuel oil transfer, lubricating oil circulation and steering gear systems, internal gear pumps are widely adopted for their compact structure and high output flow per unit volume.

In fuel transfer, where heavy fuel oil has high viscosity and wide temperature variation, the internal gear pump's viscosity tolerance allows stable delivery across different oil temperatures and grades. In lubricating oil circulation, low pulsation output helps reduce pipework vibration and bearing supply pressure fluctuation. Internal gear pumps also have relatively few wearing parts, offering maintenance advantages over alternatives such as screw pumps.

Selection requires confirming that pump body materials meet classification society requirements, that shaft seal form suits the engine room environment, and that the mounting arrangement allows maintenance access in confined spaces.

5. Food: High-Viscosity Product Transfer

Chocolate mass, syrups, jams and edible oils require pump materials that meet hygienic standards while preserving product characteristics during transfer. Stainless steel versions of internal gear pumps with food-grade seal configurations can satisfy hygiene design requirements.

Technically, the internal gear pump's low pulsation output helps maintain stable feed to downstream filling or forming processes, reducing product weight variation caused by flow fluctuation. Its relatively simple internal flow path also facilitates cleaning, suiting production lines with frequent product changeovers by shortening cleaning time.

Selection considerations include whether the pump body uses stainless steel or other food-contact-compliant materials, whether seals hold relevant certifications, and whether the pump supports clean-in-place procedures. For food products containing particulates, assess whether inter-tooth clearances allow particle passage without jamming.

Cross-Industry Selection Points

Drawing together the application logic across five industries, internal gear pump selection can be reduced to several common dimensions:

Displacement and speed matching: Determine operating speed from required system flow and pump displacement, ensuring the pump runs in its efficient range. Positive-displacement pump flow is approximately linear with speed, allowing flexible regulation through variable-speed drive.

Pressure rating verification: Check rated and peak pressure capability against system maximum working pressure and possible pressure surges. Different internal gear pump series differ in pressure rating, so select according to actual duty.

Viscosity tolerance assessment: Based on the medium's viscosity range, confirm whether suction performance and volumetric efficiency meet requirements. High-viscosity duties require particular attention to suction port design and whether auxiliary supply is needed.

Medium compatibility: Pump body, gear and seal materials must be compatible with the medium. Corrosive media require corrosion-resistant materials; food and pharmaceutical applications require hygienic configurations.

Mounting interface: Confirm flange standard, shaft specification and port orientation match the existing system to avoid increased retrofit cost from interface mismatch.

Suction condition verification: Self-priming height, inlet vacuum and suction pipe diameter must fall within the pump's allowable range, with forced-feed supply or larger suction piping used where necessary.

Internal gear pumps are not superior to every other pump type in all duties. Manufacturing cost is relatively high, tooth profile machining is complex, and in extremely low-viscosity media or ultra-high-pressure duties they may be less suitable than plunger pumps. However, where low pulsation, high viscosity tolerance and compact structure are required, the internal gear pump's technical advantages rest on clear engineering principles. Understanding the reasoning behind these advantages is more useful for correct selection than memorising specific figures.