Abstract: A pilot valve assembly for use with a main valve apparatus coupled to a water pipe, includes a differential pilot valve apparatus, and first and second pilot valve apparatuses. An inlet of the differential pilot valve is coupled to a junction and an outlet is coupled to the first pilot valve apparatus. The differential pilot valve is responsive to a pressure differential to open the differential pilot valve apparatus for water to flow to the first pilot valve apparatus and to close the differential pilot valve apparatus to inhibit water flow to the first pilot valve apparatus. The second pilot valve apparatus is coupled to the junction to facilitate flow of water through the second pilot valve apparatus when the second differential valve member is in an open position. Adjustment mechanisms facilitate adjustment of the pressures responsive to which the first pilot valve member and the second pilot valve member close.

Abstract: An automatic control valve has a main valve member moveable between open and closed positions thereof in response to pressure applied to a first piston or diaphragm in a first control chamber. The valve member moves to modulate flow through the valve to maintain desired flow conditions. Pilot pressure signals are generated to reflect the flow conditions, usually upstream and downstream from the valve, which signals are processed to generate a control signal which is fed to the first control chamber to control pressure therein. Normal movement of the valve produces wear which causes leakage of the diaphragm or seals oft he piston causing loss of primary control of the valve member which tends to fail "open". This causes an initial rise in flow through the valve which is detected by the pilot pressure signal but because of the leakage, is unable to correct.