hydraulic ram

noun2

1. •
   A hydraulic cylinder with a piston activated by pumping hydraulic fluid into the cylinder.

   • The lifts are operated by means of a hydraulic ram with wire ropes, which derives its pressure from a small pump driven by an electric motor. — 1961
2. •
   A water pump in which a flow of water is intermittently halted by a valve so that the flow is forced upward through an open pipe, usually into a reservoir.