The Function of Solenoid Valves

The magnetic force is used directly to open or close the magnetic armature, which controls the flow of the fluid.

The performance is limited by the coil, the pressure, and the size of the valve orifice. For directly operated valves, the minimum operating pressure is 0 bar; the maximum pressure depends on the selected valve/coil combination.

Examples:
Series 121
Series 146

To control a higher flow, pilot operated valves must be used. The supply pressure enters the directly operated "pilot section," which directs the flow to a "control chamber," which in turn applies the control pressure over a larger area (usually a diaphragm or piston). Therefore, a large force is generated to move the main sealing elements against a higher pressure or over a larger orifice.

A condition for operation is to have a minimum differential pressure to switch the valve. In most applications, this is not a particular problem (see the section on Magnalift Valves). The rated pressure of the valve starts between 0.1 to 0.5 bar (depending on the valve).

(NOTE: Pilot operated valves are also referred to as servo-assisted valves).

Examples:
Series 321
Series 7321B

Magnalift valves combine the features of directly operated and pilot operated valves. A mechanical connection between the piston and the diaphragm allows the valve to operate as a directly operated valve at low pressures and as a pilot operated valve at higher pressures.

Magnalift valves are specifically designed for applications where no pressure is required for valve actuation and where a higher flow than in directly operated valves is present.

Example:
Series 221