A hydraulic vehicle seat system providing powered adjustment of the position of a seat or seat portion. The system comprises a pump, flow controller, and hydraulic actuator arranged in a hydraulic circuit. The actuator includes a first and second system protection valves for the respective inlet and outlet of the actuator. The system protection valves are adapted to be activated in response to pressure within the actuator exceeding a predetermined threshold level. When activated the system protection valves close off the respective inlet and outlets to hydraulically isolate the actuator and hydraulic fluid within the actuator from the remainder of the hydraulic circuit and adjustment system. This protects the remainder of the circuit and system from excessive pressures which may be generated within an by the actuators under crash loading.