Double-acting cylinder

A double acting cylinder in an engine is one in which the working fluid acts alternately on both sides of the piston. This is in contrast to a Single Acting Cylinder, in which the working fluid acts in one direction only.

Double acting cylinders are common in steam engines but unusual in internal combustion engines. In both types of engine, inlet and exhaust valves are required at each end. In an internal combustion engine, an ignition device and/or fuel injection device is also required at each end.

In order to connect the piston to an external mechanism, such as a crank shaft, a hole must be provided in one end fitted with a gland to prevent escape of the working fluid.