What is the role of the brake chambers in a pneumatic air brake system?

BRAKE CHAMBERS (service chambers) are the air-to-mechanical energy conversion devices at each wheel. CONSTRUCTION: A cylindrical metal housing divided by a large rubber diaphragm; an inlet port for service air; a push rod connected through the center of one housing half; and a return spring to release the push rod when air is released. OPERATION: APPLY — air enters, pushes against the diaphragm, diaphragm pushes the push rod out; push rod moves the slack adjuster arm, which rotates the camshaft, which pushes brake shoes or pads against the drum or rotor; the mechanical force is proportional to the air pressure applied; RELEASE — air exhausts through the treadle valve when the driver releases the pedal; the return spring pushes the push rod back; slack adjuster pulls the cam back; shoes or pads retract. SPRING BRAKE CHAMBERS (PIGGYBACK): Most CMV brake chambers are combination service-and-spring chambers (called 'piggyback' or type 30/30 chambers). The front half is the service chamber (described above); the rear half contains the large coil spring for the parking/emergency brake; a separate spring brake port uses air pressure to HOLD the spring compressed (released); when air drops, spring expands and applies the brake from the rear. INSPECTION POINTS: Look for cracked or swollen chamber bodies (can indicate diaphragm failure); push rod should not be exposed beyond approximately 1 inch at rest; listen for air leaks around chambers; inspect mounting hardware for tightness.