Abstract: An improved discharge valve comprises an upper housing, an upwardly movable main valve assembly within the housing and forming with the upper part thereof a variable volume upper chamber, a restricted passage between the upper chamber and the exterior thereof, an outlet leading down from the lower part of the housing, a seat for the main valve assembly at the entry to the outlet so that, in the lowered position of the main valve assembly, the outlet is blocked against ingress of fluid in which the device is immersed, and a pilot stem actuable remotely from the housing to put the upper chamber in free communication with the outlet. The arrangement being such that, once 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 latter to unseat thereby permitting flow of the immersing fluid into the outlet and its substantially complete discharge.