WayneLee wrote:
OK, I think we have a problem here.........
Air pressure retracts the brakes. It's the BIG SPRING that applies the brakes. Air pressure acts against the spring releasing the brakes.
No... only in the parking brake mode, normal operation is pull the parking brake out air is released from the parking brake canister brake is applied by the spring. Push in the parking brake button in, air pressurizes the parking brake canister and the coach is able to roll.
apply the foot brake air is applied to the normal brake system stopping the coach, foot pressure is released from the pedal and the air that stopped the coach is released, allowing the coach to roll.
If you loose all air pressure, the parking brake will come on by spring pressure. to tow a air brake system you must apply air to the system, or use the "T" bar spring retraction tool to release the parking brake.
Emergency stop feature on most systems is simply a valve that is held closed by normal air pressure, when the pressure drops below a set pressure the valve opens and dumps all the air left in the tanks into the normal stop side of the normal system bringing the coach to a quick stop. when the tanks pressure bleeds off the parking brake will hold the coach from rolling away.