Medium Duty Operator's Manual - Peterbilt Motors Company
Medium Duty Operator's Manual - Peterbilt Motors Company
Medium Duty Operator's Manual - Peterbilt Motors Company
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STARTING AND OPERATING THE VEHICLE<br />
• Modulates spring brake application in proportion to<br />
front service application in the event of a rear service<br />
failure.<br />
• Prevents compounding of service and spring applications.<br />
Relay valve (full truck): speeds up the application of the<br />
rear service brake. It also incorporates a quick–release<br />
feature.<br />
Brake Proportioning (BP-R1) valve (tractor): this valve<br />
delivers air to the tractor's service brake chambers. It<br />
automatically proportions the drive axle brake app<br />
lication pressure when driving bobtail (without a trailer<br />
connected). Proportioning the brakes allows full use of the<br />
steer axle brakes and reduces lockup of the drive axle<br />
brakes. The bobtail brake proportioning system is automatically<br />
turned off when a trailer is connected.<br />
Quick–Release Valve: speeds the release of air from the<br />
brake chambers. When air is released, the air in the brake<br />
chambers is exhausted at the quick-release valve, rather<br />
than exhausting back through the treadle valve.<br />
USING THE BRAKE SYSTEM<br />
Single Check Valve: allows air flow in one direction only.<br />
Parking Brake Valve: yellow diamond-shaped knob. It<br />
controls the application and release of the parking<br />
(spring) brakes of truck or tractor-trailer combinations or of<br />
the tractor alone. If the air system is being charged from<br />
zero pressure, the parking brake valve will not hold in the<br />
release position until the system pressure exceeds 60 psi<br />
(414 kPa), which is the pressure required to override the<br />
load of this valve's plunger return spring.<br />
Trailer Supply Valve (tractor): The Red octagonalshaped<br />
knob protects the tractor system; it functions in<br />
conjunction with the parking brake valve (yellow). The<br />
trailer supply valve is responsible for synchronizing the<br />
tractor and trailer parking and emergency brakes. If the air<br />
system is being charged from zero pressure, the trailer<br />
supply valve will not hold in the applied position until the<br />
system pressure exceeds 50 psi (345 kPa). It automatically<br />
pops out and exhausts air if supply air pressure<br />
drops below 60 psi (414 kPa).<br />
Tractor Protection Valve: The functions of this valve are<br />
to (1) receive all pneumatic signals pertinent to the operation<br />
of the trailer brake system, (2) transmit these signals<br />
<strong>Medium</strong> <strong>Duty</strong> (R05/09) Y53-6008A – 117 –
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