What Is a Pilot Diaphragm Solenoid Valve?

    Normally-closed (NC) multi-media solenoid valves use an NC pilot solenoid. Normally-open (NO) versions, used where rapid closing is critical, employ an NO pilot solenoid.

NC Design – Working Principle & Features:
    When de-energized, the plunger closes the pilot drain port under spring force. Inlet pressure (P) flows through a small orifice into the diaphragm chamber, creating higher pressure above the diaphragm. Combined with spring force, this pushes the diaphragm down to seal the main valve seat.
    When energized, the pilot opens, venting the diaphragm chamber. Since the pilot vent orifice is larger than the inlet orifice, chamber pressure drops rapidly. When upward force from P exceeds downward force, the diaphragm lifts, opening the main valve.

NO Design – Working Principle:
    When de-energized, the plunger opens the pilot port and closes the vent (R). The diaphragm chamber vents, allowing inlet pressure to lift the diaphragm and open the main valve.