Discharge valve

A discharge valve device for immersion in a fluid in a cistern, the device comprising an upper housing, an upwardly movable main valve assembly within the housing and forming, with the upper housing, a variable volume upper chamber, a restricted passage between the upper chamber and an exterior of the upper chamber, an outlet extending downward from a lower part of the upper housing the outlet having a seat rim for the main valve assembly so that, in a lowered position of the main valve assembly, the outlet is blocked against ingress of immersing fluid in which the device is immersed, and a pilot stem actuable remotely from the upper housing to put the upper chamber in free communication with the outlet, the arrangement being such that, when such free communication is established, fluid escapes the upper chamber and the change in relative pressures above and below the main valve assembly causes the main valve assembly to unseat thereby permitting flow of the immersing fluid into the outlet and substantially complete discharge of the immersing fluid from the cistern, the cessation of flow of the immersing fluid enables the main valve assembly to revert to a seated position with the pilot stem cutting off said free communication, and air penetrates the upper chamber and on replenishment of the immersing fluid a net downward pressure is created on the main valve assembly to keep the main valve assembly seated, and the pilot stem is hollow and communicates to atmosphere above a normal full set level of the immersing fluid in the cistern, the main valve assembly and the hollow pilot stem defining therebetween an annular passage.