reference numerals in this embodiment the compressor discharge pressure p d is coupled directly at all times via the conduits 50 and 54 to the pressure ratio servo 64 which is identical with the embodiment of fig1 and functions to provide a predetermined control pressure p c for application to a fuel flow regulator 20 through a switching valve 14 however the position of the valve ball 38 of the switching valve 14 is controlled by a pressure differential switcher 112 which in turn is operated by a fluidics comparator circuit 110 as shown in fig2 the fluidics comparator circuit 110 is coupled to the ram air pressure p r by a line 17 and to the control pressure p c by a line 19 the comparator circuit 110 is pneumatically driven by the compressor pressure p d via a line 51 and exhausted via a line 53 the circuit functions to fluidicly compare the magnitudes of the two pressures p r and p c and to provide an amplified differential output to the differential switcher 112 this amplified pressure differential output is supplied to the switcher 112 via either a line 114 or a line 116 depending upon which pressure p r or p c comprises the lesser of the two pressures as will be explained the pressure differential switcher 112 includes a pair of flexible diaphragms 118 and 120 biased by a spring 119 and separated by a vented chamber 122 the diaphragms are both connected to an actuator rod 124 which has a central offset portion 126 and extends through a sealed flexure pivot 128 in a wall 130 the opposite end of the actuator rod 124 is connected to a.