A hydraulic press is a device which is used for lifting a heavy or large load by the application of a comparatively much smaller force than is required to lift the load mechanically or manually. Hydraulic press used in industries are generally converted or built to crush or to press any “process" or the “product". For example, this may include steel plates, aluminum rolls, metallic ores, etc.

The system is a very simple example which demonstrates the operation of a basic hydraulic system. It has two simple cylinders connected to each other, containing an adequate quantity of hydraulic fluid in it. One of the cylinders is larger in size when compared to the other. Both the cylinders have pistons in them, but in strict “hydraulic" terminology, the larger piston is called as a “ram" and small one a “plunger". A small force “P" applied on the plunger, in the downward direction, presses the hydraulic fluid below it. This pressure is transmitted equally in all directions and raises the “ram". The heavier load placed on the “ram" is thus lifted up.