by injecting into or removing from a control pressure chamber metered quantities or doses of fluid doses are metered by timed openings of solenoid valves connecting the control pressure chamber to supply or return pressure sources special valve means are provided for moving the actuator piston to a preferred position in the event of control system failure and means are included for administering very small doses consistently without recourse to special extra fast response solenoid valves application_number US 2734379 A description referring now to fig1 one embodiment of my actuator is shown having a housing incorporating a pair of coaxial cylindrical bores 12 and 14 of unequal diameter positioned in bores 12 and 14 on a common shaft 16 which may be connected to a desired device to be actuated are a pair of pistons 18 and 20 for use in a gas turbine fuel control the smaller diameter piston 18 may cooperate with orifices in housing 10 to define the fuel metering area the operating fluid then being fuel pistons 18 and 20 in association with the bores 12 and 14 define three control pressure chambers 22 24 and 26 chamber 24 communicates through a passage 28 in housing 10 with a source of hydraulic fluid or fuel under substantial pressure p s chamber 26 communicates through a passageway 30 with the return side of the fluid pressure source p r or with a sump chamber 22 is a control pressure chamber p.