PURest Air Dryer constantly purging/leaking

[Ronmar]

I am having the same issue with the air dryer purging about every 30 sec with the old style. I then read through the TM and it said replace the air governor because when I take the control line off I feel air coming through (when line is off no purge) so I Put a new governor on with no change and since i want to upgrade to the newer style like yours. I installed the Haldex PURest air dryer today and I still have the same issue. so after soaking all connections with soapy water everything showed tight but still have the issue.

Could the new Governor be bad because I still feel air coming out of the control line when unhooked?

Other possible issue in my haste to beat the incoming rain I switched the main line form the governor with the wet tank link so basically running air backwards through the dryer I notice this mistake after about 45 sec of no air pressure building on the gauge. do I need to rebuild the purge valve thinking messed something up internally.

any support apricated
sorry to drag up an old post but it appeared to be closest to what I am experiencing

When you say control line are you referring to the line connected to the purge port on the dryer? You have a large airline in from the compressor, you have a large airline out to the wet tank and you have a small line in from the governor. When the governor sees its set pressure in the tank and unloads, it sends air down that little line to open the purge valve. When the governor again starts sending compressed air to the dryer, it removes that air from the purge valve so it can close and send dried air along to the wet tank. So if you disconnect the line to the dryer purge, and it has air coming out of it, if you then open the wet tank valve and drain all its air, the governor should see the pressure drop, call for more air and stop sending that air to the purge valve line… if that happens, then the governor sounds like it is doing its job.

you put on a new governor, did you adjust it to unload at 125 PSI in the wet tank?

you said soaped all connections, did you soap EVERY connection and line on the truck? You didn’t say you were constantly purging, you said you were purging every 30 seconds or so. You only get a purge/woosh when the compressor unloads, and that woosh is only for a second or two as the dryer vents the air it has stored in a particular spot to back flush the filter and dryer media. if it does that every 30 seconds, then it sounds like the compressor is cycling on and off every 30 seconds in response to a large air leak on the truck… y0u can unscrew the wet tank valve and screw in a pressure gauge to observe what the wet tank pressure is doing and properly set the governor to 125PSI.

hearing leaks with the cat purring is VERY difficult. You can connect a shop air line to the front red glad-hand. This will fill the air system without the engine running. Make sure you are on level ground with the wheels chocked as this also releases the parking brakes just as if the vehicle was being towed…
I listen first, then I feel(touch every fitting and line) and then I bubble… cycling every 30, should be a leak bad enough to hear…

 

[Khann]

General you are correct I should've started a new thread
Ronmar I did the test on the governor you suggested and it does appear to be working
This coming weekend I will connect a gauge to the wet tank and hook up shop air and look for a leak

 

[No-0ne]

I wanted to post this picture here to see if anyone knows where these pieces of spring are coming from. I’ve been have trouble getting my new purchased M1088 home to Utah from North Carolina. I made it to Tulsa Ok today and started loosing air. I pulled over and noticed the new air dryer I just replaced in Johnson City TN was consistently purging air. I barely made it back to Tulsa without being able to touch the brake as the pressure was down to 80 PSI. Just as I pulled into the parking lot of the mechanics the emergency brakes locked up. We pulled the purge valve filter off the top and there was a little oil in it and some other tiny debris along with one of the three pieces in the photo. We fished that out and then pulled the purge valve off and two more pieces fell out. One of the pieces was stuck in the valve not allowing it to seat. The are the same pieces as in the OP’s picture above. What are they coming from? What is coming apart? Could these have come from the compresso?

 

[Ronmar]

Looks like part of the compressor ex valve spring coil. There is a firly recent discussion on it where general showed some pics of a bad one…

 

[GeneralDisorder]

That's the exhaust valve spring(s) from your compressor. Welcome to FMTV air compressor foolishness. Here is the thread Ronmar mentioned:

Who are the experts on the Air compressor

So I have oil contamination in my dryer / the compressor is prob due for a rebuild or replacement . While I was reading up on the oil in dryer stumbled across some big rig sites and there was a post stating how most compressors will push oil due to 3 things , Blocked / restricted air intake ...

www.steelsoldiers.com

 

[No-0ne]

So is the compressor about to go completely out? Is it not recommended to try and drive another 1300 miles?

 

[GeneralDisorder]

So is the compressor about to go completely out? Is it not recommended to try and drive another 1300 miles?

Definitely not. If it hasn't already, it could punch a hole in one of the compressor pistons. Which will cause it to pressurize the crankcase and blow out every seal in the engine. That's how mine died on the way home from TX with my truck. Fortunately I made it here and the compressor died a few days after I arrived home. But it started having problems 100 miles from home and I got very lucky because it probably drove another 10-20 miles after I arrived before it let go completely and punched a hole in a piston. Had to replace the whole thing.

If you are lucky you can rebuild the head alone and keep driving. If you are unlucky you will have to source a whole compressor and they are not easy to find. This compressor is rather uncommon actually. Being primarily used on our trucks. They are a higher volume unit than what would normally be equipped on our engines. Because military.

 

[No-0ne]

Definitely not. If it hasn't already, it could punch a hole in one of the compressor pistons. Which will cause it to pressurize the crankcase and blow out every seal in the engine. That's how mine died on the way home from TX with my truck. Fortunately I made it here and the compressor died a few days after I arrived home. But it started having problems 100 miles from home and I got very lucky because it probably drove another 10-20 miles after I arrived before it let go completely and punched a hole in a piston. Had to replace the whole thing.

If you are lucky you can rebuild the head alone and keep driving. If you are unlucky you will have to source a whole compressor and they are not easy to find. This compressor is rather uncommon actually. Being primarily used on our trucks. They are a higher volume unit than what would normally be equipped on our engines. Because military.

Oh boy… Every seal in the CAT engine??? The last little bit of driving I did today the truck felt sluggish? Do you think I’ve already blown all the seals? Thanks so much!! If my luck so far is any indication of how my luck is going to go with this truck I’m in trouble.

 

[GeneralDisorder]

Oh boy… Every seal in the CAT engine??? The last little bit of driving I did today the truck felt sluggish? Do you think I’ve already blown all the seals? Thanks so much!! If my luck so far is any indication of how my luck is going to go with this truck I’m in trouble.

So the problem is - worse on the later trucks where the compressor is fed inlet air from the intake manifold at boost pressure (25+ psi) - is that if it punches a hole in a piston (which I have seen twice now so mine was not an outlier) then the exhaust valve becomes the hole in the piston and it shoves air directly into the compressor crankcase which is open to the engine crankcase. They share oil for lubrication. So driving at high RPM and WOT with a ventilated piston air compressor will shove air into the crankcase at like 30+ psi.... And yeah that will blow seals and expel huge amounts of oil from the breather. Hopefully it just comes out the breather and that's what happened to mine but when it let go I was just revving the engine in my parking lot trying to build air pressure and instead of air pressure I got about a gallon of oil out of the breather - it was violent and sudden like the truck gave birth to an oil baby. It was weird and frightening.

 

[No-0ne]

I haven’t got any oil dumping out so hopefully I’m ok. ???

Do you know the part # for the compressor? So I can start looking around?

 

[GeneralDisorder]

These guys have a listing for them with all the part numbers:

Air Compressor Caterpillar 3116 Diesel Engine FMTV LMTV

Air Compressor Caterpillar 3116 Diesel Engine FMTV LMTV

www.easternsurplus.net

 

[No-0ne]

This says it’s for the CAT 3116. I have the CAT C7. Do you know if they are compatibl?

 

[GeneralDisorder]

They all use the same compressor. It's still used on the A1P2. Military never changed it.

 

[No-0ne]

That’s good news! Thanks!

 

[No-0ne]

I’m rebuilding my compressor head and there is a special tool needed to remove and replace the Inlet Valve Cages. Others have figured out other solution for this tool, but I thought I would share mine. It’s $390 for the OEM tool, mine was almost free.

 

[No-0ne]

Talking with GeneralDisorder, a better option would be to make it out of an impact socket to make filing and softening up the edges easier. I was able to file down the edges on mine but it took quite a bit of filing because that socket steeel is so hard. And according to GD you don’t want sharp edges. You need to be carful when removing and installing the new valve cage that you don’t break it. It’s cast steel.