Installation that parking brakes and piping arrangements into a vehicle air brake system will vary, relying on the vehicle make.
You are watching: A parking brake system is not required if your service brakes are fully functional.
Control valves will certainly vary, depending upon the manufacturer and form of piping arrangements.
The type of spring-loaded valve presented (Fig. 32) requires that the driver push the switch to relax the parking brakes. If the air press in the system falls below around 70 psi (483 kPa), the spring brakes may start to drag and if the falls between 20-45 psi (138-310 kPa), will completely apply. On plenty of vehicles the parking brake regulate valve ~ above the dash will close, yet some valves might never close. The important thing is that the feather brakes are completely applied before the air is depleted. Always ensure the spring brakes have actually been fully applied. Similar types the spring-loaded valves call for you to pull the button out to relax the parking brakes.
Note: ~ above some more recent models the park brake switch will no pop out automatically. However, the brakes will certainly still apply. There is a toggle manage valve in use that go not have an automatic brake application feature. The park brakes will certainly gradually apply as the air push is depleted, however, the regulate valve will certainly not move. When air pressure is restored, the park brakes will release if the toggle valve is no manually relocated to the park brake “on” position.
CAUTION: absorption the brakes happens when a organization brake application is made v the park brake still applied. This can result in damaged brake components and possibly brake failure. To stop compounding, the park brake need to be released prior to a foot brake application is made.
Note: An anti-compound line (see Fig. 34) is periodically installed between the delivery side of the main circuit relay valve and the manage side of the relay valve operating the spring brakes. When a brake applications is made, the relay valve operating the spring brakes it s okay a signal native the service brake to release the feather brakes v the same amount the pressure used to the service brakes. This prevents service-brake and spring-brake push from absorption on the brake linkages.
System charged - regular running condition
With air push of 70 psi (483 kPa) or better acting top top the emergency diaphragm (A) and piston (B) in the spring hold-off cavity, the feather (C) is totally compressed and also the piston (B) is organized in the exit position. This walk not influence the company diaphragm (D) or organization push plate and rod (E).
Park and also emergency application
When you operatethe park regulate valve, wait is tired from the feather hold-off cavity. The spring (C) is now permitted to extend, forcing the piston (B) and the diaphragm (A) forward. The piston (B) forces the service diaphragm (D) and service push plate and also rod (E) front compressing the return feather (F) and also applying the brakes. To release the park application, the park control valve is placed in the releaseposition, publication the brakes as described under “System charged - normal running condition.”
During a controlled service brake application, air pressure enters the organization port and acts upon the service diaphragm (D), which pressures the business push plate and rod (E) forward, using force come the slack adjuster. The slack adjuster rotates the camshaft and also applies the brakes. The emergency feather is organized in the compressed position by air press in the spring hold-off cavity.
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