DIAPHRAGM ACTUATED SPOOL VALVE

1408992 Valves JOHNSON SERVICE CO 9 March 1973 [30 Aug 1972] 11492/73 Heading F2V A pilot valve comprises a housing formed of three plastics discs 18, 19, 20 and a cover 21 clamping a diaphragm activator 45 to which a valve member 5 is attached, the valve member 5 being reciprocable between a pair of flexible valve seats 29, 37 which form three chambers 33, 38 and 22. The chamber 33 is open to atmosphere via port (36) (Fig. 3, not shown); 38 is connected to the main valve via part (39) (Fig. 5, not shown); 22 is connected to a vacuum source. An inlet chamber 7 is formed above the diaphragm to which a signal is applied by a relay 10 or shut-off valve 51. The diaphragm is biased to the upper position. If relay 10 is opened, atmospheric pressure is admitted to it which causes the valve member 5 to move downwardly giving a vacuum signal at outlet (39) since the valve seat 37 is uncovered to allow the vacuum source to communicate with the chamber 38. If the relay 10 is closed, the chamber 7 is isolated, the vacuum in chamber 22 passes to the chamber 7 via passages 50, 47 to equalize the pressures in the two chambers, and the valve is biased upwardly by the fluid pressure acting on differential areas of the diaphragm. In the raised position of the valve member the outlet (39) communicates with atmosphere via chamber 33 and port 36.