Power Systems Braking Fundamentals (Hydraulic and Pneumatic)

Braking systems

Convert a driver’s command into a controlled friction force at the wheels to slow or hold a machine.

Hydraulic brakes

Brakes that use fluid pressure to create braking force, utilizing an incompressible liquid (brake fluid).

Pneumatic brakes

Brakes that use compressed air to create braking force.

Input force

The force applied by the driver through the brake pedal or hand.

Master cylinder

The hydraulic component that converts input force into fluid pressure.

Brake booster

A component that reduces the driver effort needed to apply the brakes.

Brake lines

Pipes and hoses that carry pressurized brake fluid to the wheel brakes.

Proportioning valve

A valve that balances braking force between the front and rear axles.

Disc brake assembly

A braking system where pads clamp onto a rotating disc (rotor) to create friction.

Drum brake assembly

A braking system that pushes shoes against the inside of a drum.

ABS modulator

Device that adjusts brake pressure to prevent wheel lock during braking.

Pedal ratio

The ratio of force amplification from the brake pedal to the hydraulic system.

External leak

A fluid loss from the braking system that prevents pressure from building.

Internal leak

Fluid bypassing seals within components, leading to pressure loss without visible leaks.

Air in the lines

Presence of air bubbles in the hydraulic system that can cause a spongy pedal feel.

Fluid boiling

When brake fluid gets too hot, creating vapor bubbles that reduce braking effectiveness.

Pressure imbalance

Uneven distribution of pressure across the brake system that can lead to instability.

Residual pressure

Pressure that does not fully release, causing dragging of brakes.

Air compressor

Supplies compressed air in pneumatic braking systems.

Governor

Controls the pressure build and unload cycles of the air compressor.

Foot valve

Driver-controlled valve that meters air pressure to the service brakes in air brake systems.

Relay valve

Allows a small control signal to command a larger air flow for brake application.

Brake chamber

Converts air pressure into mechanical force to apply the brakes.

Slack adjuster

Adjusts brake linkage to maintain clearance as shoes wear.

Quick-release valve

Speeds up the exhaust of air from brake chambers to improve response.

Friction elements

Components like pads or shoes that create the necessary friction to slow or stop the vehicle.

Hydraulic multiplication

The principle that allows a small input force to create a greater output force via pressure.