From 130 psi to 115 psi, air comes out of the purge valve very quickly. It was changed, no difference. What causes this?

Going to take it apart tomorrow again(it's on my dad's truck) to see if something isn't seated right.

 

If you talking about the purge valve on the air dryer, that could be an air governor problem or the purge valve itself. Both are fairly inexpensive and usually easy to install.

There is one other possibility. The truck should have 3 air tanks even if you only see 2. Often times they weld a baffel inside one to make a single tank act as two. The Primary and Secondary guages on the the dash are connected to the second and third tank in line from the air compressor. There are check valves between all of the tanks to prevent back draining of the air when problems occur. Your brakes operate from the third tank so that even if you loose an air bag on your suspension, you shouldn't loose the air for the brakes or at least not rapidly. Anyway, the check valve between the air dryer and the first air tank could be the problem. It may have some dirt or ice in it preventing it from sealing in which case that tank will drain back through the air dryer until it's empty. The other two tanks should still hold air but would likely show reduced pressure as the first tank looses it's air through minor leakage of the other two check valves.

I'm sorry If I haven't explained this well but the check valves may be the problem especially this time of year.

 

Its winter, Al.

Seriously, this time of year, no matter what happens to air loss, if the truck is staying inside of its legal requirements, I write everything else off to dirt and ice. I dont fix things that are not broken, just because it wasn't doing it last week.

I see lots of guys pouring methanol in the lines, heating up valves and smacking them with a BFH.

It usually blows the students away when they see me fix air problems with the foot valve and hand valve 99% of the time. Load the tanks up, make rapid full brake applications with both of them and see if it still does it.

I think the main reason why most air problems happen in the winter is that the tanks are not drained. It should be done everyday, all of them, including the trailers.

I am convinced that the reason why we have so little air problems is that on some days, my tanks get drained up to half a dozen times.

-35 in Cranbrook is the same as -35 in Winterpeg, except I can the Rockies from here. Nana na booboo

 

We're thinking now the purge valve doesn't fully seat, and a whole new air dryer is in order.

BTW, the old man says it has always done this(he's owned the truck for about 8 months) but is much more severe in winter.

Thanks for the tips.

 

If its a Meritor/wabco drier they use a 'pressure contolled check valve' . It replaces one of the check valve into either the primary or secondary tank. It allows some air to bleed out of the tank to wash back over the dessicant in the drier. So its normal to see one needle drop a little when it purges. Hope this helps.....

 

I like your sig pdm. I have it on the back of my toolbox. Crappy pic is from my cell:
We can fix broke
but we can't fix
STUPID

 

weve been having a lot of locked up tractors lately with the weather. i never drained the tanks, no one did. i started draining them down before i went home and havent had any issues since