12/19/2025
Air brakes, explained—fast.
Tanks store compressed air → your treadle sends a control signal → relay valves pressurize the chambers and push the shoes. If pressure drops, spring brakes set automatically (fail-safe).
Quick pre-trip checks
• Governor cut-in/cut-out ≈ 100–125 psi
• Leak test: combo ≤ 3 psi/min (engine off)
• Low-air warning: ~60 psi
• Spring brakes apply 20–45 psi
• Build-up: 85→100 psi ≤ 45 s
Save this for your Skills Test and follow for more pro tips.
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