LOWLANDER HD MK2 & WIDEBODY MANURE SPREADER – INSTRUCTION & SPARES MANUAL
Page 83
6.3.8.2 SPRING BRAKES FOR EMERGENCY BRAKING AND PARKING
All vehicles and trailers with air brakes must have a way of stopping if the service brake system fails. Using spring
brakes combines this emergency braking system with a parking-brake system.
Spring brakes are not air applied like service brakes. They apply when air pressure leaves the brake chamber and
release when air pressure builds up in the chamber.
Spring brakes use a different type of brake chamber from service brakes. A brake chamber that includes both service
brake and spring brake sections is called a spring brake chamber. Spring brake chambers apply the brakes by means of
a large coil spring that provides enough force to hold the brakes in the applied position, instead of using air to apply
the brakes.
Spring brake chambers are different in appearance from service brake chambers. To accommodate the large coil
spring, a section must be added to the service brake chamber that is clearly visible and adds significantly to its size.
The spring brake section is “piggy-backed” onto the service brake section and these two sections function as two
separate chambers. The portion nearest the pushrod end is the service brake section and it works in the same manner
as a separately mounted service brake chamber.
To release the spring brakes, normally about 414 kPa (60 psi) of air pressure must be supplied to the spring brake
chamber to compress or “cage” the spring (See Diagram 4-1). If system pressure is below 414 kPa (60 psi), the spring
brakes start applying because there is no longer enough pressure to keep them released (See Diagram 4-2).
Some trailers can still be pulled away even with the spring brakes applied because they do not have the braking power
of the full service brake application. Before pulling away the trailer, it is important to ensure that the air brake system
has enough air pressure (normally 414 kPa (60 psi)) to keep the spring brakes from applying. Due to the way most
spring brakes chambers are currently constructed, it is very difficult to unintentionally release the spring.
The large coil spring used in the spring brake chamber is compressed under very high tension. Tampering, damage or
corrosion can cause the spring to release, resulting in sudden violent motion of parts of the air brake chamber. Since
this can be hazardous, never attempt to service or repair any air brake chamber.
Diagram 4-1: Spring brake chamber - Brake not applied
Diagram 4-2: Spring brake chamber - Brake applied
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