second disc shaped seal plate 115 is fixedly mounted mid way along the shaft 109 both the seal plates are mounted co axially with the shaft the shaft and thus the first seal plate is biased in a downward direction by a spring 119 shown in fig1 as a broken line such that the first seal plate 113 abuts a rubber seal 113 a located in the base of the valve 101 the second seal plate is mounted on the shaft at such a height that it does not during normal use contact the housing water is therefore free to flow through the gap between the second seal plate and the housing and to collect between the first and second seal plates the lower portion of the housing 117 containing the rubber seal 113 a associated with the first seal plate is detachable from the remainder of the housing so that it can be inspected or replaced although the second seal plate does not contact the housing during normal use it is arranged to form a temporary seal with the housing when the lower portion 129 of the housing is removed in such circumstances the spring 119 pushes the shaft and thus the fixedly mounted second seal plate downwards the second seal plate contacts the housing forming a temporary seal until the lower portion of the housing is replaced in fig1 the valve is shown in the closed position when the water is to be drained from the tank a tool is inserted into the valve outlet from below and the shaft 109 is pushed upwards thereby lifting the first seal plate.