What pumps does the positive displacement pump include?

In the process of periodically changing the volume of the pump chamber, a positive displacement pump transfers its volume to the liquid to be transported through the periodic changes of its action and displacement, so that its pressure can be directly increased to the required pressure value to realize transportation, such as: 1) reciprocating pumps, including piston pumps, piston pumps, diaphragm pumps and extrusion pumps. 2) Rotor pumps, including gear pumps, screw pumps, Roots pumps, rotary piston pumps, vane pumps, crankshaft pumps, flexible rotor pumps and peristaltic pumps.