Reciprocating pumps include diaphragm, piston, and bellows pumps. Rotary Metering Pumps. Gear-type rotary pumps use gear teeth, lobes, or vanes to trap a fixed volume of fluid. A rotary motion carries the fluid from the inlet to the outlet of the pump. In a gear pump, for example, two meshing gears rotate in a closed cavity with minimal clearance between the gear teeth and the pump casing.
Fluid captured between each tooth and the casing at the inlet port is carried to the outlet port.
By maintaining precise volumes between the teeth and low leakage rates between each tooth and the casing, a gear pump can provide accurate metering. It is easy to achieve flow control by controlling the rotational speed of the gears. The accuracy of the control speed of the motor often determines the pump's flow accuracy. Lobe and vane pumps operate similarly, but substitute smooth lobes or vanes for the gear teeth. Rotary pumps that use gears or lobes provide low pulsation and continuous flow.