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Indirectly controlled solenoid valves normally open
2-way solenoid valves normally open servo-controlled
Main components: body with main orifice, cover with pilot orifice, diaphragm (or piston) assembly, quill + mobile core + gasket + gasket assembly (kit normally open), coil. operation: the normally open 2-way solenoid valves servo-controlled have an inlet fitting and a usage fitting. as regards the displacement of the membrane, identical to that of the normally closed 2-way solenoid valves servo-controlled, but instead of the normally closed kit, a normally open kit is mounted which opens and closes the pilot orifice. 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. there will be a minimum difference in pressure between the supply fitting and the one used to guarantee correct operation of the solenoid valve itself. However, an excessive pressure difference between the supply and the use, as on the normally open 2-way solenoid valves with direct control, causes an increase in the force required to open the pilot orifice, so if this pressure difference it is higher than the maximum value for which the solenoid valve was designed, the latter may not reopen 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.