A hydraulic actuator for vehicle steering system has a pump (22) driven by an electric motor (39) to provide pressurised fluid for the steering cylinder (11). There is a main valve (12) and a non-return valve (27) leading to a reservoir (28). The pressure is monitored by a sensor whose output signal controls the motor. The main valve is an "open circuit valve". There is a fluid tap-off from the main circuit through a control valve (26) which goes to the main valve through a check valve (31). This is upstream of the non-return valve protecting the reservoir. The motor has two speeds. Its normal speed is engaged by the starter switch for the engine whereas a higher speed is engaged by a pressure switch (42).
