Proportioning valve
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A proportioning valve is a valve that relies on the laws of fluid pressure to distribute input forces to one or more output lines. A proportioning valve can increase or decrease forces for each output, depending on the cross-sectional surface areas of those output lines.
A simple example is an input tube with cross-sectional area A entering a chamber. Leading out of the chamber are two more tubes, one with cross-sectional area 3A and the other with area A/2. If a force F is applied to the fluid in the input tube, the pressure in that tube will be F/A. Utilizing pressure laws, we find that each output tube will see the same pressure. This means the output tube with area 3A will yield a force of 3F, and the output tube with area A/2 will yield a force of F/2. Thus, if you apply a 10-pound force to the input, you will get forces of 30 pounds and 5 pounds, respectively, from the outputs.
Proportioning valves are frequently used in cars to amplify and distribute different forces to the front and rear brakes. If the driver pushes the brake pedal with a force of 10 pounds, levers and proportioning valves can amplify the force to, say, 350 pounds at the front brakes and 150 pounds at the rear brakes (a 70/30 brake bias).