Normally open mixed control solenoid valves
2-way solenoid valves normally open with mixed control. Main components: body with main orifice, cover, membrane (or piston) assembly, quill assembly + moving core assembly, coil. The normally open 2-way solenoid valves with mixed control have an inlet fitting and a fitting for use. The operation of these solenoid valves is, as far as the diaphragm movement is concerned, identical to that of the 2-way solenoid valves normally closed with mixed control, but instead of the normally closed kit, a normally open kit is mounted which opens and closes the orifice. pilot. In this case, therefore with the coil powered, the pilot orifice will be closed and therefore the membrane in a position to close the main orifice, while with the coil not powered, the pilot orifice is open causing the opening of the main orifice. Note: In this family of solenoid valves, unlike the servo-controlled ones, a minimum pressure difference between the supply and the use fitting is not necessary to guarantee the correct functioning of the solenoid valve itself. However, an excessive pressure difference between the supply and the use, as on the 2-way solenoid valves normally closed with direct control, causes an increase in the force required to open the pilot orifice, so if this difference pressure is higher than the maximum value for which the solenoid valve has been designed, the latter may not open even when the coil is not powered. For the correct operation of the solenoid valve and to avoid the rapid deterioration of the membrane, it is desirable that, when starting to close the valve, the flow rate value does not exceed Kv, i.e. the guaranteed flow rate with loss of load through the solenoid valve equal to 1 bar. For this reason, if the supply pressure with the valve open is higher than 1 bar, the use of the free-mouth valve is not recommended, i.e. without a suitable throttle on the discharge port which brings the pressure drop on the solenoid valve back to the value of 1 bar. In addition, particular attention must be paid in the design of the hydraulic circuit to the problem of water hammers, which can cause overpressures such as to tear the membrane or damage other parts of the solenoid valve.