Gear Pump
A gear pump is a positive displacement pump that moves fluid by repeatedly enclosing a fixed volume within the cavities of interlocking meshing gears, transferring it mechanically from suction to discharge to deliver a smooth, pulse-free flow proportional to rotational speed.
On the shop floor, gear pumps are installed for high-viscosity fluid transfer such as lubricating oil, asphalt, resins, and paints, as well as high-pressure hydraulic systems exceeding 200 Barg where precise volumetric dosing is required. They rely on close running clearances, ranging from microns to 0.075 mm, for self-sealing and self-priming without check valves, ensuring reliable operation in demanding maintenance environments.
- Dry running causes rapid bearing or bushing seizure within minutes due to loss of fluid lubrication and thermal expansion.
- Cavitation from inadequate NPSH or excessive speed for viscous fluids creates vacuum bubbles that implode, eroding gear teeth and housing.
- Contamination wear from solid particles bypassing tight tolerances accelerates volumetric efficiency loss below 80% of new capacity, causing internal leakage.
What distinguishes external vs. internal gear pumps?
External pumps use two identical meshing gears for higher pressure up to 4000 psi in general hydraulics; internal pumps use a rotor and idler gear for higher efficiency of 95-98% and smoother flow in high-viscosity metering and lubrication.
How is volumetric efficiency maintained under variable loads?
The self-sealing meshing action prevents internal leakage, maintaining 91-98% efficiency up to 250 bar, provided thermal expansion is managed by precision clearances.
What is the critical maintenance metric for reliability?
Flow rate at rated pressure; if flow drops below 80% of new capacity, the pump must be rebuilt or replaced due to internal wear.
Can gear pumps handle abrasive fluids?
Generally no; abrasiveness dictates external vs. internal selection and often requires jacketed bodies or specialized materials, as standard clearances are too tight for solids.
What is the primary failure mode for high-pressure applications?
Shaft side-loading or bearing collapse due to inadequate shaft support on both sides of the gears, leading to housing contact and catastrophic failure.