Abstract: An hydraulic fluid actuated power assisted steering system has an open center valve 4 adjustable in response to a steering input to control fluid flow to a power assistance ram 6. A by-pass valve 8 communicates between a pressure line 3 and a return line 7 of the valve 4. The by-pass valve has a control port 11 which is adjustable by a valve member 9 spring biased at 10 to normally open the control port 11 so that fluid flow from line 3 to line 7 by way of port 11 alleviates the generation of noise in the valve 4 and back pressure in the line 3. The valve member 9 is responsive to a predetermined fluid pressure differential developing between the line 3 and 7 when the valve 4 is operated so that the member 9 is displaced to close port 11 and direct greater fluid flow from pump 2 to the ram 6.

Abstract: A rotary valve assembly and a method of assembling such a valve has a sleeve 5 and a rotor 3 relative rotation between which from a neutral condition adjusts the valve. The sleeve and rotor are biased to the neutral condition by an encircling C-spring reacting on pins corresponding to projections 11a and 12 relatively rotatable with the sleeve 5 and rotor 3 respectively. For setting-up the valve in its neutral condition the sleeve and rotor are mounted in a jig 15 with the projection 11a of the jig engaging in a recess 27 of an adjustable component in the form of a second C-spring 24 which is intitially rotatable on the sleeve 5. The sleeve 5 is rotated relative to the spring 24 and projections 11a and 12 to determine the neutral condition by the characteristics of fluid applied through valve ports E, S, P.sub.1, P.sub.2. The spring 24 is now welded or otherwise secured to the sleeve 5.