Internal gear pumps are rotary positive displacement pumps and, although part of the gear pump family, they represent a distinct design class. At the core is an internally toothed gear connected directly to the drive shaft. It drives a smaller externally toothed gear, which is mounted off-center within the pump head. This asymmetrical arrangement creates a variable-volume pumping chamber that transports the medium from the suction to the discharge side. Lubrication is typically provided by the pumped medium itself.
Depending on the design, the fluid is conveyed horizontally, vertically, or even at a 90° angle. The pump is usually driven by a gear motor with a coupling, though direct-drive versions with magnetic couplings are also available. Flow rate and performance depend on size, gear module, speed, and design. The output can be regulated via speed control or bypass systems. Discharge pressure is determined by the system backpressure, internal leakage, and the pump’s power limitations.
Typical performance data: pressures up to 16 bar, flow rates from 0.6 to 290 m³/h, viscosities from 1 to 200,000 mPas, temperatures from -40 °C to +300 °C, and power up to 75 kW. The maximum suction lift is approximately 4 m. Internal gear pumps are primarily suited for clean, non-abrasive fluids. However, robust designs can tolerate a limited amount of solids, subject to application-specific evaluation.
These pumps are self-priming, operate smoothly, and are known for very low pulsation. Thanks to their compact design and minimal number of components, they are also low-maintenance and cost-effective.
Available sealing options include gland packings, lip seals, single and double mechanical seals, and magnetic couplings. Materials include cast iron, cast steel, stainless steel, and other special alloys upon request.
