Abstract: A hydraulic spool valve 40 (FIG. 2(a)) of the edge control type in which the peripheral ends 31, 33 of a spool land 47 cooperate with a radial service port 41 to define by axial spool position the the closure of the port 41 and degree of opening to supply or return port 18, 19. The spool 25 is located in a sleeve 14 itself located in a housing 11 and O-ring seals 22', 22" inhibit leakage between sleeve and housing beyond the seals. Leakage fluid up to the seals exerts a contracting force onto the sleeve and when the spool is in a neutral position closing the service port stiction occurs between the sleeve and the end 36 of the spool land closest to the return port.

Abstract: In a fluid control valve, a force acting on the spool is produced by the inevitable inclination of the fluid flow into the spool chamber, and the force tends to be balanced by the fluid flowing over first and second surfaces of the spool, the inclination of the fluid flow as it leaves the spool chamber to a return port being less than, and of opposite sense to, the inclination of its entry. The fluid is received from the spool chamber by a chamber associated with the return port, the return port chamber being shaped to divert a portion of the fluid. In a known valve construction, the portion of the fluid is diverted to re-enter the spool chamber, to enhance the balancing force.