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.