Fluid control system utilizing pressure drop valve

Abstract

A steering control system is disclosed of the type utilizing a variable fluid delivery source, such as a variable delivery pump, providing fluid to a steering cylinder, the flow to the steering cylinder being controlled by a steering control valve. The steering control valve includes a first orifice which is variable between a minimum orifice area permitting a minimum system flow and a maximum orifice area corresponding to a maximum system flow. The variable fluid delivery source is maintained at a generally constant level above the steering load as the system flow varies between the minimum and maximum flow rates. Disposed in series flow relationship between the fluid delivery source and the steering control valve is a second valve including a valve member defining a second variable orifice operable to maintain a relatively constant pressure drop across the second valve as the system flow varies between the minimum and maximum flow rates. The pressure drop across the second valve may be changed by changing or adjusting the biasing force on the valve member and therefore, the same steering control system may be utilized with any of several different pump control (standby) pressures by changing the pressure drop across the second valve, without the need for changing the configuration of the steering control valve and its variable orifice, because the steering control valve will, in each case, be subjected to approximately the same control pressure differential.