Flow-control system having a wide range of flow-rate control

In combination, a pilot valve and a main valve for controlling delivery of pressure fluid from an upstream source to a downstream load;

• said pilot valve comprising a pilot-valve body with a passage between an inlet connected to said source and an outlet-line connection and having a valve-member seat therebetween, a flow restriction between said seat and said outlet-line connection, a pilot-valve member coacting with said seat, solenoid-operated means for applying to said pilot-valve member a valve-opening force proportional to solenoid-excitation, and fluid-pressure operated means differentially responsive to pressure on opposite sides of said flow restriction for establishing a constant delivery of pilot-valve outlet flow in said outlet-line connection for a given solenoid excitation and substantially independent of changes in source pressure;
• said main valve comprising a main-valve body having a passage between an inlet connected to said source and an outlet-line connection to said load and having a valve-member seat therebetween, a flow restriction in said outlet-line connection, whereby near said last-mentioned restriction there exists a first region of relatively low-pressure main-valve outlet fluid flow and a second region of relatively high-pressure main-valve outlet fluid flow upstream from said main-valve outlet flow restriction, fluid-pressure responsive means for operatively positioning said main-valve member and differentially responsive to pressure on one side for developing main-valve opening force and on the other side for developing a balancing force in opposition to the opening force, and a connection from said second region to said other side for developing balancing force from main-valve outlet pressure sampled from said main-valve outlet restriction;
• first means including a throttling orifice connecting the pilot-valve outlet-line connection to said first region, and second means connecting the pilot-valve outlet-line connection to said one side of the fluid-pressure responsive operating means of said main valve;
• whereby, depending upon the excitation of said solenoid, pilot-valve flow will be delivered to said load essentially with a first characteristic of proportionality to solenoid excitation;
• and further whereby main-valve flow will be additionally delivered to said load essentially with a second and steeper characteristic of proportionality to solenoid excitation, the pilot-valve flow rate at which said second characteristic becomes operative being a function of the setting of said throttling orifice.