its steady state value at about time t 0 corresponding to the termination of the flow mode the mass flow controller 22 fig1 is commanded u201c off u201d shortly thereafter i e 0 5 sec or less pneumatic on off valve 24 is actuated to close such that fluid flow decreases from the steady state rate to zero generally simultaneously with the actuation of valve 24 signal pressure is discontinued to regulator 50 to remove the differential pressure setting in this regard the operation of valve 24 and regulator 50 advantageously may be synchronized under the control of a common signal pressure with the differential pressure setting being removed the setting of regulator 50 effectively is reduced to 12 psi inasmuch as the outlet pressure remains at the operating pressure of 14 8 psi the regulator closes such that the outlet pressure is maintained substantially at 14 8 psi depending upon the length of the no flow period and or on the interval typically about 0 5 sec between when the no flow mode is initiated and when the control pressure signal is removed to effect the closing of the regulator the outlet pressure may increase slightly to perhaps 15 psi over the period u03b4t 0 it will be appreciated however that by virtue of the controlled differential pressure setting no appreciable creep effect is evident even when the system is operated with very long intervals i e 1 hour or more.