Back in December 2017, I did a pictorial of how to service/clean the Wabco Unloader Valve..
Unfortunately it didn’t take long for the now perfectly working unloader valve to show me an old hidden problem… It seem that the previous owner of the coach never did bother to replace the original Air dryer filters.. It is not uncommon for people not to bother to replace the filters in the dryer because, firstly the manufacturer often state that the filter does regenerate himself each time it blows air out of the unloader valve, and secondly because like in this case, the two filter do cost as much to replace as buying a complete newer unit..
Most new units these days are built as one piece, as you have the dryer and the unloader in the same unit, where in my case the Unloader Valve was a separate unit from the dryer… Back In December the Unloader did stop working and after I manage to clean the unit and reinstalled, it only took few times of the engine running to show the fact that the reason for the Unloader to be so dirty was because the dryer had also stop working, because completely full of crap, by blowing air out of the bottom membrane hole instead of the outlet valve..
In a perfect world, yes, the dryer may regenerate itself for several years, but when the compressor start to push down the line oil mixed with water and very hot air, an ugly mix is created and this kind of beige paste get stuck inside the dryer, until the dryer once completely full let the mix past into the Unloader Valve…
The dryer is designed to cope with water and air, not oil! I guess this is the main reason why all new unit have cheaper replaceable cartridges and the Unloader is build directly under the filter in the same unit.. The cheaper cartridges offer an incentive to at least replace it every couple of years and the Valve built directly below does show at once if oil is passing the piston ring of the compressor..
One thing that I need to stress out, as even my good friend mechanic was not aware of, is that not all Unloader and compressors need an external Governor to work, in the same way as not all air system have the purge tank for the dryer..
In my case, my system did not have either the Governor or the purge tank, and that did confuse the situation a little because I still had a bundle of hoses coming in and out between the dryer and the unloader. I did try to buy the original dual dryer and when I eventually did find one on Ebay in England.
The vendor first sent me an email confirming the delivery, then, the day after he sent me another email where it state that he couldn’t find any longer that unit and that therefore he had refund my money. Imagine my surprise when the day after I find the exact same unit from the same vendor for sale again, but this time at more than double the price. Some people never change and I truly feel sorry for this guy, but that gave me the incentive required to perform a much need it upgrade to my air system.
To cut the story short I ended up buying and using what they call an universal air dryer as it can be use in any of the main 4 possible combination air systems. I only wanted a single cartridge system as I don’t use the trailer or have more than three axle to operate, but dual filter are still the best option for trucks with trailers, if they get use a lot like driving in the city…