acts to positively block all flow so that the flush valve is not exposed to low pressure conditions in which it may not operate reliably the diaphragm seals against leakage from the housing 28 while permitting movement of the valve structure 54 with very little resistance to valve movement the friction resulting from an o ring seal or other sliding seal is eliminated as a result the opening operation of the valve in response to inlet pressure is highly sensitive and the control stop 16 opens reliably at the threshold pressure established by the spring force imposed by spring 78 this spring force can be selected to accurately determine a threshold opening pressure and this feature can be used to provide improvements in multiple flush valve systems fig5 illustrates a flushing system including a number or bank of eight flush valves 22 a 22 h each flush valve is supplied with water from a corresponding control stop 16 a 16 h all preferably having generally the structure of the control stop 16 illustrated in fig2 4 the bank of flush valves 22 a 22 h is supplied with water from a source 88 of pressurized water through a common header 90 connected to all of the supply conduits 12 the flush valves 22 a 22 h require a residual pressure to keep them closed therefore in the event of an interruption in the water supply some or all of the flush valves 22 a 22 h may be.