What is the purpose of the bleed screw or valve (bleeder) in a hydraulic braking circuit?

Question

DentroTest · Accepted Answer

In a hydraulic braking system, the force is transmitted through the brake fluid, which is incompressible by nature. If air enters the circuit, it will be compressed when the pedal is pressed, producing a spongy feel and a dangerous loss of braking effectiveness. The function of the bleeder is to make it easier to extract and drain that air so that the circuit is filled exclusively with fluid. Serving as a filler opening is not its function, because filling is done directly at the reserve reservoir of the master cylinder. Regulating and limiting the maximum pressure is not either, because modulating and limiting pressure depends on regulating or brake force regulator valves, not on bleed screws.

What is the purpose of the bleed screw or valve (bleeder) in a hydraulic braking circuit?

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