62 through a threaded plug 68a or similar mechanical means a stepped down portion 64a of the valve member 64 extends into a chamber 71 defined by the bore 67 ports 73 are formed through the spool member 64 to provide fluid communication between the chamber 72 formed by the bore 63 which is fluidly connected to the restriction 70 and the conduits 74 and 76 an annular axially extending undercut 62a is formed in the body 62 adjacent the ports 73 a stepped piston 98 which includes an enlarged end portion 98a and a stepped down portion 98b is slidingly received in the body 62 the enlarged end portion received in the piston bore 103 and the stepped down portion 98b received in the sealing bore 69 and extending into the chamber 71 a threaded fluid connector 97 is engaged in the bore 105 to retain the piston 98 and provide communication between the chamber defined by the bore 103 and a conduit 96 fluidly connected to the piston master cylinder assembly 42 of fluid actuated brake system 26 to prevent mixing of fluids from the brake system 26 and the fluid power control system 24 the chamber defined by.