What are the parts of an air brake system

An air brake system is built from several coordinated groups of components: air supply and treatment (compressor, governor, air dryer), air storage and management (reservoirs, check and protection valves, drains), control valves (foot treadle, relay and quick‑release valves, parking controls), actuators and foundation brakes (service and spring brake chambers, slack adjusters, S‑cam or air‑disc hardware), safety and monitoring (gauges, low‑pressure warning), tractor–trailer interface hardware (gladhands, protection valves), and modern electronics (ABS/EBS with sensors and modulators). Together, they generate, store, manage, and modulate compressed air to safely apply, hold, and release vehicle brakes.

The core groups of components

Air supply and treatment

These parts generate compressed air, control its maximum pressure, and remove moisture and oil before air reaches the brake circuits.

• Engine-driven air compressor: Pumps air into the system; may be gear- or belt-driven, sometimes water-cooled and oil-lubricated.
• Governor: Commands compressor “cut-in” and “cut-out” pressures (typically ~100 psi/690 kPa cut-in and ~120–135 psi/830–930 kPa cut-out).
• Air dryer with purge valve: Removes moisture and oil vapor (desiccant cartridge); purges automatically at cut-out to prevent ice/rust.
• Aftercooler/heat exchanger: Lowers air temperature to improve drying efficiency.
• Oil separator/coalescing filter (where fitted): Further reduces oil carryover to protect valves and seals.
• Compressor intake filter and unloader mechanism: Ensures clean intake air and allows compressor unloading at cut-out.

Together, these elements ensure a reliable, dry air supply at controlled pressures, improving brake responsiveness and longevity.

Air storage and management

After generation, air is stored and routed through protective devices that isolate faults and keep priority functions supplied.

• Reservoirs (tanks):
  

  • Supply/wet tank: First stop after the dryer; collects residual moisture/oil.
  • Primary and secondary service reservoirs: Separate circuits (e.g., drive axle vs. steer axle) for redundancy.

• Check valves (one-way): Prevent backflow and cross-bleed between circuits.
• Multi-circuit/pressure protection valves (MCPV/PPV): Prioritize and isolate circuits so a leak doesn’t drain the entire system.
• Safety/pressure relief valve: Vents if system over-pressurizes (often set around 150 psi/1030 kPa).
• Drain valves (manual pull-cords or automatic): Remove accumulated moisture/oil from tanks.

This stage preserves system integrity, ensuring each brake circuit retains adequate pressure even if another circuit develops a leak.

Control valves and driver’s controls

These components translate driver intent into controlled air pressure at the wheel ends and manage service, parking, and emergency functions.

• Foot brake valve (dual-circuit treadle): Proportionally meters air from primary and secondary reservoirs to the service brakes.
• Relay valves: Speed brake applications by delivering air locally at axles based on control signal pressure.
• Quick-release valves: Rapidly exhaust air from chambers for faster brake release.
• Parking brake control (yellow push–pull): Applies/releases spring brakes via a supply/emergency circuit.
• Trailer hand control (if equipped): Allows independent trailer service brake application for maneuvering/testing.
• Spring brake modulating/relay valve: Controls spring brake force during low-pressure or emergency conditions.
• Proportioning/limiting valves (application-specific): Tailor axle brake force to load or traction.

By metering and relaying pressure, these valves deliver quick, stable, and balanced braking across multiple axles and circuits.

Actuators and foundation brakes

These parts convert air pressure into mechanical force at the wheels and apply it through the brake hardware.

• Service brake chambers (e.g., Type 20/24): Diaphragm chambers convert air pressure to pushrod force for normal braking.
• Spring brake chambers (e.g., Type 30 piggyback): Powerful mechanical springs provide parking and emergency braking if air is lost.
• Pushrods and clevises: Link chambers to slack adjusters; stroke length is a key inspection metric.
• Slack adjusters (manual or automatic/ASA): Maintain correct brake shoe-to-drum or pad-to-rotor clearance.
• Foundation brakes:
  

  • S‑cam drum brakes: Use cam rotation to spread shoes against a drum.
  • Air disc brakes (ADB): Calipers clamp pads onto rotors for consistent performance and easier inspection.

Properly adjusted actuators and foundation components ensure even, powerful braking with predictable pedal feel and shorter stopping distances.

Safety, warnings, and monitoring

Redundancy and alerts are built in to warn drivers of faults before braking capability is compromised.

• Dual pressure gauges: Show primary and secondary system pressures separately.
• Low air pressure warning devices: Lights/buzzers activate typically at or above 60 psi (410 kPa).
• Stop light (brake) switch: Signals brake application to following traffic.
• ABS components: Wheel speed sensors, tone rings, and modulator valves prevent wheel lockup and improve control.

These devices help drivers detect leaks or malfunctions early and maintain control during hard braking or low-traction events.

Tractor–trailer interface components

For combination vehicles, special hardware connects and protects the tractor and trailer brake circuits.

• Gladhands and seals: Quick couplers for service (usually blue) and emergency/supply (red) air lines.
• Tractor protection valve: Prevents trailer air loss from depleting the tractor’s system.
• Trailer supply/emergency valve: Charges trailer reservoirs and applies spring brakes if pressure is lost.
• Relay emergency valve (on trailers): Controls trailer service brakes and spring brake release from local reservoirs.
• Electrical connectors: ABS power/diagnostics via ISO 7638 and vehicle network (e.g., SAE J1939 CAN).

These components enable safe coupling, quick response at the trailer axles, and isolation in case of a line failure.

Electronic braking and stability control (modern systems)

Contemporary heavy vehicles add electronic control to enhance stability, shorten stops, and simplify diagnostics.

• ABS ECU and modulators: Independently modulate air to prevent wheel lockup.
• EBS (Electronic Braking System) ECU: Coordinates brake demand via electronics, often integrating traction and hill-hold functions.
• Stability control sensors: Yaw rate, lateral acceleration, and steering angle sensors to mitigate rollovers and jackknifes.
• Diagnostic interfaces: Support fault codes and maintenance via standardized connectors.

These systems layer electronic oversight atop pneumatic hardware for finer control and improved safety, especially under dynamic loads.

How the parts work together

The compressor fills the supply (wet) tank through the dryer until the governor reaches cut-out. Protected by check and protection valves, air charges the primary and secondary reservoirs. When the driver presses the treadle, control pressure triggers relay valves at the axles, delivering air from local reservoirs into service brake chambers, pushing rods through slack adjusters to apply S‑cams or disc calipers. Releasing the pedal vents air via quick-release and relay valves for a fast release. Parking brakes are held off by air; pulling the parking control exhausts air so springs apply the brakes. If pressure drops too low, warnings activate and spring brakes engage, while ABS/EBS modulates individual wheels to maintain stability.

Maintenance-critical parts and checkpoints

Regular inspection keeps the air brake system responsive and compliant with safety regulations.

• Air dryer service: Replace desiccant cartridge and check purge valve to prevent water/oil contamination.
• Reservoir draining: Use automatic or manual drains, especially in humid or cold climates.
• Governor settings: Verify cut-in/out pressures (about 100 and 120–135 psi) and compressor build-up time.
• Leak checks: Measure allowable pressure loss with engine off; soap-test fittings, hoses, and chambers.
• Slack adjuster and pushrod stroke: Confirm automatic adjusters function; out-of-stroke indicates issues.
• Foundation brake wear: Check shoe lining/pad thickness, drum/rotor condition, and hardware integrity.
• ABS/EBS diagnostics: Resolve fault codes; verify sensor gaps and harness integrity.

Attending to these items prevents fade, uneven braking, longer stops, and compliance violations while extending component life.

Common configurations and variations

Air brake systems share fundamentals but differ by application, performance goals, and regulatory requirements.

• Brake type: S‑cam drums dominate heavy-duty fleets; air disc brakes offer better fade resistance and simpler inspections.
• Circuit design: Dual-service circuits are standard; additional circuits may support lift axles or body equipment.
• Vehicle class: Tractors, straight trucks, buses, and vocational vehicles tune valves and sizing for their duty cycles.
• Powertrain trends: Battery-electric trucks use electric-driven compressors; duty cycles influence dryer sizing and cooling.

These variations tailor performance, packaging, and serviceability while preserving the core safety architecture.

Summary

An air brake system comprises air generation and conditioning (compressor, governor, dryer), protected storage (reservoirs, check and protection valves, drains), precise control (treadle, relay and quick-release valves, parking controls), powerful actuation (service and spring chambers, slack adjusters, S‑cam or air disc brakes), safety/monitoring (gauges, low-pressure warnings), tractor–trailer interface (gladhands, protection valves), and modern electronics (ABS/EBS). Each component plays a defined role so heavy vehicles can brake reliably, redundantly, and predictably under all operating conditions.

What are the six basic parts of a brake system?

The six basic parts of a hydraulic brake system are the Brake Pedal, Brake Booster, Master Cylinder, Brake Fluid, Brake Lines, and Wheel Brake Assemblies (which include calipers, pads, and rotors or drums, shoes). These components work together, using hydraulic pressure to convert the driver’s foot pressure on the pedal into frictional force that slows or stops the vehicle.
 
Here’s a breakdown of each part’s function:

1. Brake Pedal: The starting point of the system, it’s the pedal the driver presses to initiate braking. 
2. Brake Booster: This component uses vacuum to multiply the force applied by the driver’s foot on the brake pedal, making it easier to apply significant braking force. 
3. Master Cylinder: Often called the “heart” of the system, it converts the mechanical force from the pedal into hydraulic pressure. 
4. Brake Fluid: A hydraulic fluid stored in a reservoir, it transmits the pressurized force from the master cylinder to the wheel brakes. 
5. Brake Lines: These metal and rubber tubes carry the pressurized brake fluid from the master cylinder to the wheel brake assemblies. 
6. Wheel Brake Assemblies: This collective term includes:
   • Brake Calipers (for disc brakes): Clamps that hold the brake pads. 
   • Brake Pads (for disc brakes): Friction material that is squeezed against the rotor. 
   • Brake Rotors (for disc brakes): Metal discs attached to the wheel that slow down as the pads grip them. 
   • Brake Drums and Brake Shoes (for drum brakes): Found on some vehicles, where shoes press against the inside of a drum to create friction. 

What are 7 steps air brakes?

Click here for help finding your state’s manual.

• Step 1: Turn the Key to the “On” Position.
• Step 2: Fan the Service Brake Below 90 PSI.
• Step 3: Identify Air Pressure Levels.
• Step 4: Perform a Safety Start.
• Step 5: Fill the Air Chambers.
• Step 6: Apply and Hold the Service Brake.
• Step 7: Check and Record Air Pressure.

What are the main components of the air brake system?

A COMPRESSOR, to pump air. A RESERVOIR OR TANK, to store the compressed air. A FOOT VALVE, to regulate the flow of compressed air from the reservoir when it is needed for braking. BRAKE CHAMBERS & SLACK ADJUSTERS, the means of transferring the force exerted by the compressed air to mechanical linkages.

Which of these parts would you find on a disk air brake system?

Components of disc air brakes include rotors, calipers, brake pads, slack adjusters and brake chambers. Components of wedge air brakes include brake drums, brake shoes and linings, spiders, dust shields and brake chambers.