This type of valve is actuated by pressure acting on a piston or diaphragm. The fluid is usually neutral e.g. air, water, hydraulic oil. The pressure range varies and is specified accordingly in a data table.
"Normally Closed" (N/C) valves of this type remain closed under spring pressure, when de-activated.
"Normally Open" (N/O) valves of this type remain open under spring pressure, when de-activated.
When pressure is connected to port "Z" the valves open or close according to type.
A separate 3/2 pilot valve is used to supply pressure to port "Z", it is mounted either directly on the actuator or remotely.
In some cases a 4/2 or 5/2 pilot valve will be required. The main valve position can be N/C or N/O. The basic position is determined by connecting the pilot valve output lines accordingly. (The direction of flow is usually indicated by an arrow or shown schematically on the body).
