Most solenoid valves with a fitting size over ½” make use of the servo-assisted principle, this uses the pressure in the fluid supply to open and close either a piston or (more commonly) a flexible rubber diaphragm. This allows a smaller more economical solenoid coil to be used than would be the case with a direct acting solenoid valve. Servo assisted valves can frequently be identified by the requirement in their data sheet for a minimum differential pressure (typically 0.1 – 0.5 bar). To operate successfully these valves rely on the use of small diameter (<1mm) holes. If these holes become blocked the valve will refuse to open or close correctly even if the solenoid operator can be felt or heard working when the valve is electrically operated.

If the valve won’t open the hole that the solenoid operator controls is blocked – so the solenoid operator should be dismantled and cleaned. Particular attention should be paid to the small orifice that the solenoid armature opens and closes, depending on the model this may be centrally over the flexing diaphragm or at the outlet end of the valve body.

 

Should the valve not close the hole in the diaphragm itself is probably blocked, this hole may be located in the rubber diaphragm or somewhere in the diaphragms central hub.

 

If these holes are blocked, they should ideally be cleaned under clean running water (or some other appropriate fluid) – if it is necessary to push something into the blocked hole to clean it care should be taken not to change the diameter of the hole as this will have been carefully sized by the valve maker for best performance.