These 2 port poppet valves fullfill many requirements not coverd by other types of valves. They are simply on-off valves and two are required to operate a single acting cylinder. A double acting cylinder would require four valves. Two port valves are particularly suitable for locking purpose on hydro-pneumatic circuits, in whice case the port connection is reversed.

The valves for vacuum use are identical to the others, except that the seal on the poppet is reversed.

A feature of these valves is the isolation of the pilot chamber from the main supply, by a vent to atmosphere.