A piston pump moves fluid in gulps. It has valves that slam, a stroke that stops and reverses, and a delivery that pulses. For a press that is fine. For anything that must be fed continuously — a lubrication system, a burner, a hydraulic circuit — it is a nuisance.

A gear pump has no valves and never stops. Two meshing gears turn inside a close-fitting housing. Where the teeth come out of mesh on the inlet side, space opens and fluid is drawn in. Each tooth space then carries its trapped charge around the outside, between the tooth and the housing wall, to the outlet. There the teeth go back into mesh, the space closes, and the fluid is pushed out.

The mesh itself is the seal. Fluid cannot take the short path back across the middle of the pump because the teeth are in contact there — which is why a gear pump needs no check valves at all.

It is positive displacement: a fixed volume per revolution, so flow follows speed and barely notices pressure. That is the opposite of a centrifugal pump, whose output collapses as back-pressure rises. The trade is that a gear pump will happily keep pumping into a blocked line until something bursts — which is why the next blueprint in this batch exists.

⚠ Attribution is genuinely contested. Johannes Kepler is credited with a gear pump around 1600–1604, a model of which was made by the Prague clockmaker Jost Bürgi in 1604. Gottfried Heinrich Graf zu Pappenheim is credited with a two-axis rotary pump in 1636. We state both; the mechanism is not in doubt.

Fluid Mechanics

Blueprints (56)

Ammonia Refrigeration Machine

Refrigerated Ship

Liquefying Air

Vapour-Compression Refrigeration

Hydraulic Brake

Gear Pump

Hydraulic Jack

Variable-Displacement Axial-Piston Pump

Bourdon Pressure Gauge

Safety Relief Valve

Hydraulic Accumulator

Hydraulic Ram Pump

O-Ring Seal

Hydraulic Press

Screw Propeller

Hydrostatic Balance