Air Brake Valves

AnythingTruck.com is a distributor of name-brand air brake parts. This includes air brake valves made by Bendix, Midland/Haldex, Sealco, and Wabco, and we've made these valves available to the public at discounted prices. We also offer many aftermarket replacement valves from companies like Velvac and Pro Trucking Products for customers that want an even better price.

Truck and Trailer Air System Tech Tips

General Air System Valve Troubleshooting

Valve leakage is commonly caused by, but not restricted to:

1. Contamination caused wear, damage, or sticking of the valve's operating parts
2. Application of air pressure to a valve's delivery port from another device in the air system

Determine the port(s) improperly emitting air pressure and perform the following service checks:

1. Exhaust port leakage at rest - Disconnect the delivery lines. If the leak stops, inspect the device at the other end of the delivery line for leakage. If the leakage continues, inspect and repair or replace the leaking valve.
2. Delivery port leakage at rest - Consult the appropriate service manual for specific test procedures.
3. Exhaust port leakage during application - Consult the appropriate service manual for valve specific test procedures.

Always blow out all attaching lines and reservoirs when installing a replacement valve to purge any contamination from the system. Avoid using thread sealant or tape as excess material can itself contaminate the air device.

D-2 Air Governor

Never condemn or adjust the governor pressure settings unless you have checked pressure with an accurate test gauge or a dash gauge that is registering accurately. Standard dash gauges are only required to be accurate to within +/- 10 percent.

Remember the following if adjustment is necessary:

1. Turn the adjusting screw counter-clockwise to lower the air pressure setting.
2. Turn the addjusting screw clockwise to increase the air pressure setting.
3. Be careful not to overadjust. Each quarter turn of the adjusting screw raises or lowers the pressure setting approximately 4 psi.
4. The cut-in and cut-out range is not adjustable.

The most common cause of governor failure is contamination. Blow out all attaching lines, hoses, etc when replacing a governor. Make sure the reservoir pressure sensing line is routed from the reservoir so that no contamination may enter the line and pass into the governor. A replacement D-2 air governor can be found here.

Air Compressor Troubleshooting

Always replace the discharge hose when replacing your compressor!

Compressors that are passing excessive oil as evidenced by the presence of oil at valve exhaust ports or seeping from air inlets is usually a result of:

1. Restricted air intake - Check the compressor air filter and replace as necessary. Check the compressor air intake hose for kinks, excessive bends, and a minimum ID of 5/8".
2. Restricted oil return - Do not use sealers on mounting gaskets as this could result in diminished oil return on some compressors. Check the bottom oil drain line on compressors that use this feature to ensure that there are no bends where oil could pool and that the minimum ID is 1/2".

Causes of slow air pressure build times are:

1. Dirty intake filter or restricted intake line
2. Restricted discharge line or compressor discharge cavity
3. improperly functioning unloaders or governor

Common causes of high head pressure and resulting failure are:

1. Discharge line is kinked or clogged with carbon
2. Water traps in discharge line causing line freeze-up
3. Discharge line smaller than the minimum recommended 1/2" ID