An electrohydraulic doser actuator of the kind comprising a step piston the axial position of which is variable as a function of metered doses of pressurized fluid which are vented to or from a control chamber by a first on-off valve connecting the latter to a high pressure source or a second on-off valve connecting it to a low pressure source, said valves being normally closed and thus establishing a hydraulic lock on the piston to maintain same in its last reached axial position.;In order to improve the precision of positioning of the piston (58, 60), the invention provides for a pair of additional on-off valves (52, 53) mounted in parallel relationship to the main on-off valves (51, 54), respectively, and having a smaller opening than said main valves for the control of small adjustments of the position of the piston.;For use particularly in gas turbine control systems.
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