Your air brake system can produce a number of issues, and it’s not always easy to find the solution. Here are a few great fault finding tips that will go a long way in finding and fixing the problem with your brakes.
The Problem: Slow Air Pressure Build-up
Here are a few possible causes and suggestions:
- Restriction in the compressor inlet pipe.
- Compressor cylinder head gasket leaking.
- Restriction in the compressor delivery pipe. (Check for carbon build-up).
- Unloader piston in the compressor head sticking. (On American compressors).
- Unloader valve cut-out pressure set too low.
- Blocked air dryer cartridge.
- Bad leak somewhere in the brake system. (Couple workshop air supply line directly into the Air Dryer inlet port and listen for air leaks without the engine running.
- Couple an air gauge directly onto the end of the compressor delivery pipe to check the performance.
The Problem: Air Dryer Constantly Purges
Here are three possible causes:
- Bad leak in the delivery pipe between the air dryer out port and the multi-circuit valve inlet port.
- Faulty check valve at the unloader in the air dryer.
- Air leaks in any of the multi-circuit valve delivery pipes.
The Problem: The Multi-circuit Protection Valve
Here are a few possible suggestions:
- Circuits 21 and 22 should open up first to allow pressure to supply the main service brake system via the Foot Bake valve. The opening pressure of these two circuits are normally set at about 6 to 6.5 bar.
- After the service brake pressure has built up to about 6,5 bar, the third and fourth circuits (23&24) open up at about 7 bar to supply pressure to the park brake and trailer control systems, as well as the Auxiliary system.
- If these pressure settings are not set correctly, it is possible to be able to release the Park brake and the Trailer brakes, without having enough air pressure in the Service brake system to apply the vehicles service brakes.
The Problem: Air Pressure Only Builds Up to Around 6.5 Bar
Here’s what you can look for:
1) Usually the problem is due to a bad leak in circuit 23 or 24. As mentioned above, circuit 21 and 22 start opening up at about 6,5 bar and build up until about 7 bar, when circuits 23 and 24 open up, indicating that there must be a bad air leak in one of these circuits, preventing the system to build up to its maximum operating pressure. One of the most common reasons for this is a leaking Park brake actuator (Spring Brake booster).
2) It is easier to find an air leak if the engine is not running. That is why it is a good idea to couple the workshop air pipe into the beginning of the air system, like into the inlet of the Air Dryer or into the Compressor delivery pipe, for example.
The Problem: The Quickest Way to Establish the Reason for an Air Brake Valve to Leak
- The numbers that are cast into all the valves should be remembered like this. Any port beginning with the number 1, (i.e. 11 or 12 etc.), are air supply ports and are continuously supplied with air pressure when the system is charged. Any port beginning with the number 2, (i.e. 21 or 22 or 23 or 24 etc.), are air delivery ports. Any ports beginning with the number 4, (i.e. 41 or 42 or 43 etc.), are signal, or control, ports. Ports marked with a number 3 indicate that it is the exhaust port.
- If a valve is leaking through its exhaust port, remove all the fittings out of the ports beginning with the number 2. If after you have done this, the valve still leaks, then the valve is faulty. However, if the valve stops leaking then it is a good indication that there is another valve somewhere down the delivery pipe line that is feeding pressure back, causing it to leak through the valves exhaust port. Establish which valve, or unit is causing this feed-back and replace that unit.
With these handy tips, you’ll find it much easier to determine the problem within your air brake system and make the necessary repairs. Need the help of an expert? JMR specialises in brake systems and parts and we uphold the highest standards in workmanship. Contact us today for all your brake system needs.