Abstract: Metering slots in valve spools are useful for modulatably controlling fluid flow through a control valve. The current metering slot configurations used in a meter out condition have high flow forces acting on the spool or metering areas that open or increase in size rather slowly relative to the valve spool movement. The subject metering slot is formed by plunging a ball-end end mill cutter into a control face of a valve spool at an acute angle and then moving the cutter laterally to provide the desired width of the metering slot. The resulting metering slot provides a metering area that increases in size rather quickly with a rather small increment of movement of the spool with the flow forces generated by the fluid passing through the metering slot being relatively low.

Abstract: A hydraulic system (9) includes a hydraulic motor (10), a main control valve (17) for controlling said motor (10), a make-up valve (78,79) operatively associated with said main control valve (17) and a vent line (93,94,95,99) for selectively venting said make-up valve (78,79). In such hydraulic systems, and in particular, in prior art hydraulic systems used to raise and lower a load, there is always the possibility that should hydraulic pressure not be maintained in the vent line the make-up valve could come open and the load could unexpectedly move. Such a situation could occur with, for example, air trapped in said vent line and the simultaneous failure of a pump of the system. The present invention solves this problem by providing pressure maintaining arrangement (200) in fluid communication with said vent line (93,94,95,99).