Metering pumps can be referred to as dosing pumps or proportioning pumps. The purpose of the metering pumps is to add small quantities of liquid into other liquid streams or vessels. A metering pump should be able to deliver measured volumes of liquid accurately without significant changes when the pressure alters. The flow accuracy can vary from +/-0.25% to +/- 3%. Metering pumps are often small plunger pumps, peristaltic pumps or diaphragm pumps.

The plunger pumps used for this process are slightly different from the standard plunger pumps. The main difference involves a variable stroke mechanism. This makes the flow adjustable while the pump remains running at a constant speed. Theoretically the pump can operate from zero to maximum flow. Practically it is from 10%-100% flow.

A metering pump is a single cylinder pump. When combining more pumps the pumps can be used as multiple units. This is suitable when different liquids have to be metered. For every cylinder the stroke is adjustable to deliver the right amount of volume.

There are two designs for the diaphragm metering pumps. The small diaphragm metering pumps have the diaphragm driven directly by an electric solenoid. The stroke length is mechanically adjustable and the stroke speed is electrically adjustable. The large diaphragm metering pumps have the diaphragms driven hydraulically. The hydraulics are controlled by a plunger pump.

The plunger type pumps are used when there is no risk of corrosion and the liquid is not toxic. The plunger pump can be used for all pressure ranges.
The diaphragm pump is used when the pump has to be leak free. Since metering pumps operate relatively slowly, high-viscous liquids aren't a problem.