Peterbilt Medium Duty Trucks Operator's Manual after 1-07
Peterbilt Medium Duty Trucks Operator's Manual after 1-07
Peterbilt Medium Duty Trucks Operator's Manual after 1-07
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Operating Instructions<br />
Compressed Air Tanks: The wet (supply) and dry (service)<br />
tanks are located behind the battery box and on the frame<br />
rail; the supply tank is below the front service tank. See “Air<br />
Tanks” on page 162.<br />
The wet tank receives air from the air dryer and cools it<br />
somewhat, allowing moisture to condense for draining. Relatively<br />
dry air is then supplied to the two service tanks for distribution<br />
to their respective brake circuits. The service tanks<br />
are isolated from each other by check valves.<br />
Dual Service Brake Treadle Valve: delivers air to the two<br />
service brake circuits.<br />
Double Check Valve: directs the higher air pressure from<br />
either the rear (primary) or front (secondary) service tank to<br />
the modulating valve.<br />
Modulating Valve (SR–1): used only on full trucks, not tractors.<br />
It performs four functions:<br />
• Limits spring brake hold-off air pressure delivered to the<br />
spring brake chambers.<br />
• Provides a quick release of air pressure from the spring<br />
brake chambers to speed spring brake application.<br />
Using the Brake System<br />
• Modulates spring brake application in proportion to front<br />
service application in the event of a rear service 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 feature.<br />
Brake Proportioning (BP-R1) valve (tractor): this valve<br />
delivers air to the tractor's service brake chambers. It automatically<br />
proportions the drive axle brake app<br />
lication pressure when driving bobtail (without a trailer connected).<br />
Proportioning the brakes allows full use of the steer<br />
axle brakes and reduces lockup of the drive axle brakes. The<br />
bobtail brake proportioning system is automatically turned off<br />
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 />
Single Check Valve: allows air flow in one direction only.<br />
<strong>Medium</strong> <strong>Duty</strong> (R10/06) Y53-6008 – 87 –
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