Plunger type pumps are essentially ‘Metering Pumps’ and should be considered, first, as precision instruments used to feed accurately a predetermined volume of liquid or semi-solid into a process or system. Their secondary function is to pump, or move or transfer a fluid from one point to another. They contain special adaptation of the conventional positive displacement reciprocating class of pumps, which are designed primarily to transfer fluid at an accurately controlled rate. They differ in that the metering pump’s pumping rates can be varied by changing the effective stroke length.