Abstract: A lockable hydraulic power-assisted steering system for steering one or more wheels of a vehicle, the system comprising: a hydraulic pump (1) having an inlet (2) and an outlet (3); a hydraulic reservoir (4) having an inlet (5) and an outlet (6); said pump inlet (2) being connected to the reservoir outlet (6); a hydraulic power steering housing (7a), the steering housing being operable by means of a steering wheel and the steering housing having an inlet port (8) and an outlet port (9); a hydraulic circuit, including: a pressure conduit connecting the pump outlet (3) to the steering housing inlet port (8), a return conduit connecting the steering housing outlet port to the reservoir inlet (5), a user operable lock valve (10) which selectively allows to connect and disconnect the steering housing inlet port (8) from the pump outlet (3) and/or to connect and disconnect the steering housing outlet port (9) from the reservoir inlet (5), characterized in that at the inlet port (8) of the hydraulic power steering ho