Air systen cycles (blows off pressure) every three seconds

Good post.....I'm not that familiar or comfortable with how the air brake systems function at the level discussed above, but this conversation has brought up some good info that is well worth remembering.

bob b wrote:
New update. It was the check valve! This is a small one inch rubber face metal disc that works with a spring to maintain pressure. It is located in the dryer just under the fitting for the large hose connection. I removed it and found damage to the rubber seal. Good news,! It is easy to change, cheap, and rewarding to fix. Thanks to the help on this topic. Bob

Thanks for given us the update Gary

bob b wrote:
New update. It was the check valve! This is a small one inch rubber face metal disc that works with a spring to maintain pressure. It is located in the dryer just under the fitting for the large hose connection. I removed it and found damage to the rubber seal. Good news,! It is easy to change, cheap, and rewarding to fix. Thanks to the help on this topic. Bob

Bob,
I really want to thank you for getting back and posting the remedy for this issue. First off, not many do and second, I've seen this issue, your same problem, in here and a couple of other RV forums, a few times and, I don't recall seeing what the remedy was. Thanks again.
Scott

New update. It was the check valve! This is a small one inch rubber face metal disc that works with a spring to maintain pressure. It is located in the dryer just under the fitting for the large hose connection. I removed it and found damage to the rubber seal. Good news,! It is easy to change, cheap, and rewarding to fix. Thanks to the help on this topic. Bob

My guess would be the unloader valves in the compressor. If it acessable you may not have to remove the compressor.

A little more information for you. The air governor does few things along with its job of regulating the air pressure. When the pressure get to the set point, it stop (unloads)the air compressor. I am use to heavy equipment so, I am guessing the RV's system would be the same way. To unload the compress air is used to open the compressor valves(Unloading valves) so it will not pump air under pressure. At this time the air governor will also send air under pressure to the air drier to open the dump valve to let the air drier dump out any moist air from it tank. The Air drier Check valve will keep the air in the air tank up to pressure for a good length on time is your air system is tight. As your system air pressure drop to the triggering point, the air governor will release the Air compressor unloading valve and the air drier dump valve. At this point the compressor will start to fill your air system back up. Gary

An update. I spoke with a tech rep at Haldex and he thought that it was not the check valve but rather the unloader in the compressor. I went ahead and ordered the check valve as it was only $15 so we'll see what happens. I really don't want to have to remove the compressor, i can't even see it! Bob

Thanks guys! I knew someone would have good suggestions. Tomorrow I'll look at the check valve and get back with my findings. Bob

All air dryers will have that check valve, and indeed it can stick open as suggested. Since the governor gets it's system pressure somewhere after that check valve it can be that the system pressure is dropping really fast where the governor gets it's signal, yet not where the pressure gauge gets it's signal. Good suggestion!

Brian

Does your air drier have a check valve between it and the air tank? It is possible that the check valve is bad, and your air pressure is draining out during the purge cycle. causing your system to recycle fast. Replacing the Air drier would be my very last try. Good luck Gary