A Hydraulic cylinder (also called a linear hydraulic motor) is a mechanical actuator that is
used to give a linear force through a linear stroke.
Hydraulic cylinders are able to give pushing and pulling
forces of millions of metric tons, with only a simple hydraulic system. Very simple
hydraulic cylinders are used in presses; here the cylinder consists out of a volume in a
piece of iron with a plunger pushed in it and sealed with a cover. By pumping hydraulic
fluid in the volume, the plunger is pushed out with a force of plunger : area mulitiplyied by its pressure.
More sophisticated cylinders have a body with end cover, a piston-rod with piston and a
cylinder-head. At one side the bottom is for instance connected to a single clevis, whereas
at the other side, the piston rod also is foreseen with a single clevis. The cylinder shell
normally has hydraulic connections at both sides. A connection at bottom side and one at
cylinder head side. If oil is pushed under the piston, the piston-rod is pushed out and oil
that was between the piston and the cylinder head is pushed back to the oil-tank again.