The rigid, plastic insert molded into the diaphragm has a raised seat against which the soft tip, solenoid plunger seats with no need for critical registry, thus allowing greater clearance between the plunger and guide. The insert includes a depending boss which cooperates with the outlet to throttle flow during closure to reduce water hammer. The necessary bleed hole is in the insert for greater precision and uniformity of operation. The diaphragm material is molded to include a spacer preventing seating the bleed hole against the cup-like portion of the guide with consequent inability to close.