Section 10 --- Chassis Information
The Executive 2005
438
Brake Systems - Back-Up
The motorhome air braking system is equipped with several back-up safety systems and warning
alarms in the event of air system failure. For example: should the air compressor fail to charge the
air system and low air gauge readings go undetected, a low air pressure warning buzzer will sound
and a low air pressure dash warning indicator lamp will illuminate. These warning indicators occur at
approximately 65 psi. This will alert the operator of an impending situation. If the motorhome is
allowed continued operation, the pneumatic emergency spring brake relay valve, installed in the
air system, senses the low air pressure condition and will release the air charge from the spring
brake air chambers on the rear drive axle. In this case, the park brakes will automatically apply at
approximately 30 psi. This safety back-up system acts as an automatic emergency brake system.
Another back up safety is the air system separation of the front and rear brakes, implemented by
using two air tanks. One tank is located in the front and the other is located in the rear. This separation
allows the front air tank to operate the front brakes; the rear tank operates the rear drive axle brakes
and tag axle brakes. This tank division gives reassurance in case one tank experiences a failure of
an accessory air item allowing the compressed air to escape.
Accessory air items are other pneumatically operated items such as the air horn, step well cover,
vacuum generator, etc. The accessory air items operate only when air tank pressures exceed 65 psi.
This is done with pressure protection valves. Should an accessory air item fail, the pressure protection
valve (PPV) reserves the remaining air pressure of 65 psi for braking. This will leave the motorhome
with one air tank fully charged for safety back up.
In another situation, whereby all compressed air has escaped from the rear air tank, a pneumatic
back-up safety valve is installed. This is the safety inversion valve. The inversion valve senses the
absence of rear air tank pressure. In this case the inversion valve will allow the operator to make a
modulated spring brake application, made in conjunction with the emergency spring brake relay valve.
The inversion valve allows the front air tank pressure to recharge the rear brake chambers after the modu-
lated spring brake application has been made. This back-up system implements use of all the brakes,
allowing the operator to bring the motorhome a safe stop. In case of all compressed air charge escaping
from the front air tank, the operator will still have full use of the rear brakes.
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