Abstract: A power steering system is disclosed which selectively controls the flow of fluid to a steering motor and an auxiliary device, and may have as its source of pressurized fluid either a fixed displacement pump, a variable displacement pump, or a load sensing pump. The system includes a steering control valve disposed between the pump and the steering motor, and an externally pilot operated flow control valve, specifically, a priority valve, disposed between the pump and the steering control valve, such that the entire system flow enters the priority 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.