A control stop for a flush valve for a urinal or toilet fixture includes a housing defining a flow chamber divided by a valve seat into inlet and outlet sections. A valve structure is biased toward the valve seat by a spring applying a valve closing spring force. The housing is sealed by a diaphragm, and the diaphragm covers the movable valve structure, isolating it from water flowing through the housing. The diaphragm does not impede valve structure movement, and the closing spring force establishes a threshold water supply pressure for opening the control stop during increasing pressure following a no or low supply pressure condition. A plurality of control stops may supply a bank of flush valves and fixtures, and open in a cascading sequence during increasing pressure as a result of having springs with different closing spring forces.