A metering pump precisely controls the flow rate of a liquid by pumping it in a continuous succession of small doses. They can only be used for liquids because liquids are incompressible; they occupy the same volume independently of their pressure. For that reason, metering pumps are positive displacement pumps — the pumping mechanism moves only the exact amount of liquid that it is set to deliver in one revolution or one stroke. When working correctly, a metering pump will have no leakage or slippage from input to output or vice versa.
Metering pumps are widely used in laboratories, chemical plants, medicine, and commercial vending. When used in medicine, they can mete out exact amounts of medications to patients over a period of time. For manufacturing, they assure the right amounts of ingredients are measured into production processes. In commerce, metering pumps make sure customers receive all of the liquid that they have purchased. Metering pumps are often used to dispense oils, syrups, and food-related items, such as a steaming cup of hot chocolate from a vending machine.