Fluid flow control apparatus

Claim 1

A priority valve for controlling fluid flow from a source of fluid to a steering circuit and an auxiliary circuit, said priority valve comprising a housing having an inlet port for connection to a source of fluid, a priority port for connection to a steering circuit, an auxiliary port for connection to an auxiliary circuit, and a pilot port for connection with a pilot flow control means in the steering circuit, the housing also having a plurality of fixed valve surfaces that at least partially define a fluid chamber communicating with said inlet port, means defining a pilot conduit communicating with said pilot port for directing a pilot flow of fluid thereto, a valve member disposed and movable in said fluid chamber to control fluid flow between said inlet port and said priority and auxiliary ports, said valve member having a plurality of axially extending lands which cooperate with said fixed valve surfaces to define a plurality of variable size orifices, said plurality of axially extending lands comprising a first land cooperating with one of said fixed valve surfaces to define a first one of said plurality of variable size orifices communicating with said inlet port and said priority port, a second land cooperating with another of said fixed valve surfaces to define a second one of said plurality of variable size orifices communicating with said inlet port and said auxiliary port, and a third land cooperating with a third one of said plurality of fixed valve surfaces to define a third one of said plurality of variable size orifices communicating with said inlet port and said auxiliary port and establishing a fluid flow parallel to the fluid flow through said second variable orifice, said second and third lands defining an axially extending circumferential groove in said valve member between said second and third lands that communicates said third variable orifice with said auxiliary port, means for exposing a first end portion of said valve member to a first fluid pressure, means for exposing a second end portion of said valve member to a second fluid pressure which is taken from the pilot flow of fluid, said valve member being movable in a first direction under the influence of a variation in a difference between the first and second fluid pressures to decrease the size of said first variable orifice and to open said second variable orifice, thereby decreasing flow to said priority port and increasing fluid flow to said auxiliary port, said valve member being movable farther in the first direction under the influence of a further variation in the difference between the first and second fluid pressures to decrease further the size of said first variable orifice, to increase the size of said second variable orifice, and to open said third variable orifice, thereby further decreasing flow to said priority port and increasing flow to said auxiliary port.