applied to inlet passageway 182 and passes through chamber 151a and the resultant port 181 opening 34 throttled 34 by piston 174 and thence through passageway 186 to a suitably connected vented tank or other low pressure source passageway 188 transmits regulated pressure p1 to the exterior chambers 142 and 144 of servo valve assembly 110 passageway 164 with incorporated orifice 162 communicates inlet passageway 182 with throttle valve chamber 153 and with servo port 114 servo flow developed through any opening of servo port 114 passes through chamber 146 and passageway 148 and is exhausted to atmosphere through interface port 149 it will be observed from the above description of the back pressure regulator shown in fig2 that the regulator will serve to maintain the pressure level of the system fluid source applied to passageway 182 as a function of the compression to which spring 112 is adjusted a pressure level greater than the set level would cause the servo valve to move against the set spring force closing servo port 114 and causing throttle valve 150 to move and open throttle port 181 and venting the pressure in passageway 182 until equilibrium is regained reverse operation would be experienced if a lower pressure level than set level.