Depamu metering pumps, a kind of reciprocating pumps evenly and stably transporting liquid in a measurable quantity, are widely applied to industries like petroleum, natural gas, chemical, electricity, environment protection, pharmaceutical, food, military, construction material, etc. and suitable for transportation of fluids with a high pressure, high temperature or strong corrosion, easy to volatile or crystallize, flammable, explosive, toxic or smelly, in a large specific gravity or high viscosity as well as radioactive metal.