GB860072A - Reverse acting gate valve - Google Patents

Abstract

860,072. Fluid-pressure servomotors ; valves. BUTLER, G. A. May 15, 1957 [Nov. 23, 1956], No. 15487/57. Class 135. In a rising stem gate valve having a pair of gate elements 30, 31, Fig. 1, urged apart by springs 32, 33 into engagement with removable seat members 22, 23, the sealing faces on the gate elements are located below the flow ports 34, 35 so that lowering the gate elements opens the valve and raising them closes it. Line pressure admitted to the valve chamber 11 due to the slight unseating of the upstream gate element regardless of the direction of flow through the valve acts upwardly on the valve stem 43 to assist closing of the valve. Each seat member is provided with a sealant reservoir 36 closed by a loose piston 41 acted upon by line pressure in the chamber 11 so that when the valve is closed the piston in the downstream seat member forces sealant through passages 80, 81 and an annular groove 82 in the seat member to seal the neck of that seat member. From the groove 82 the sealant flows through passages 83, 84, 85, 86, in the seat member gate element transfer recesses 89, 90, Fig. 6, and a circular groove 88 in the seat member surrounding the flow passage to form an effective seal between the seat member and gate element. The piston in the upstream gate member is unaffected since line pressure passing between the upstream gate element and its seat and transmitted to the underside of the piston is balanced by the pressure in the chamber 11 acting on the upper face of the piston. When the valve is opened the transfer recesses immediately isolate the sealant in the seat member passages from the circular groove 88 so that very little sealant is wasted. In another embodiment, instead of the gate being operated by a hand wheel 77 and the rising screwthreaded stem 43, pressure on the two sides of a restriction 132, Fig. 7, in a fluid-pressure line 134 acts on opposite sides of a diaphragm in an actuator 129 controlling a pilot valve 129g. When the pressure difference on the two sides of the restriction reaches a predetermined value the valve 129g opens to vent a chamber above a piston 123 mounted on the valve stem 160 so that the stem rises to close the valve. Line pressure being admitted to chambers above and below the piston 123 through the hollow valve stem and ports 23b, 19b. A rack and pinion 200, 201 is fitted at the top of the valve stem for direct mechanical operation of the valve.