Some vehicles, such as buses, may also be equipped with an EMERGENCY RELEASE TANK (2).

In this system, if main reservoir pressure is lost, the spring brakes will automatically apply.

If the parking brakes have applied because of a loss of main reservoir air, the driver can draw reserve air from the emergency release tank to release the parking brakes. A dual parking brake control (19) is used together with the emergency release tank. The driver must press on the emergency release button. Releasing the emergency release button will automatically allow the parking brakes to re-apply.

The emergency release would only be used to move the vehicle from an undesirable location, if the parking brakes had been applied due to a low main reservoir air condition.

CAUTION: Parking brakes should be in the released position before making a service brake application. A full brake application, made when the parking brakes are applied, can compound the force exerted on the slack adjusters and linkage, which could result in damage or brake failure. Compounding is the combination of two forces; the force applied by the spring brakes and the force applied by the service brake.

NOTE: Spring type brakes are primarily a parking brake, but in the event of loss of main reservoir air, they can assist in stopping the vehicle. How quickly they will stop the vehicle depends on such factors as:

• The weight and speed of the vehicle;
• The steepness of the grade;
• The spring force of the spring brakes which have been installed; and,
• The adjustment of the service brakes.