Ferranti International Plc

Antony J Wood

George F Gocher

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. Both the service port in the sleeve and the spool are constructed such that with the spool in the neutral position the spool groove 48 extends towards the return port so that the end 50 of the groove is at least in line 51 with the O-ring seal 22' and the supporting end region 36 of the spool, inevitably contacting the sleeve, does so at an axial part not subjected to a net contracting fluid pressure.

Fluid control valve

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. In accordance with the present invention, however, the return port chamber is modified so that a portion of the fluid flow is directed to form a stable vortex, the effect of the vortex ensuring that the whole of the fluid flow leaves the spool chamber at substantially the required inclination, increasing the balancing force in this manner. A second stable vortex may be formed to ensure the integrity of the fluid flow as it enters the spool chamber; and to enhance the stability of the first vortex.

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Hardingstone, United Kingdom

Antony J Wood