The pumps, which are used on board ship, can be divided into two main groups: displacement pumps and centrifugal pumps. They can be broken down into three classes: (1) reciprocating, (2) rotary, and (3) centrifugal. Under reciprocating are the direct acting, power, and crank-fly wheel types. Under rotary are the gear, vane, screw and piston types. Under centrifugal are the volute, diffuser, mixed-flow, axial flow and turbine or regenerative types
