Who are the experts on the Air compressor

[j_boucher]

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 , block or restricted oil return , or its just old . I reviewed TM's and visually looked at my compressor and only see an engine oil supply no return ? I wonder if this is a reason these seem to pump oil a lot aka maybe they are getting so hot and oil temps in them spike. I know it has in and out coolant for overheating , but again if the oil stays as old oil I'm sure lubrication proprieties go away . Just curious what the experts may know

 

[Ronmar]

The oil returns thru its connection to the timing case where he drive gear is located.

All compressors, like engines pass a certain amount of oil, a clogged intake/kinked hose can make this worse by deepening the vacuum during the intake stroke.

What are you considering "oil contamination" as that is one function of the dryer, to separate out this routine oil. If you pull it apart and you found yellowish oil/water emulsion paste, that is not uncommon, and have found it to some degree in every dryer I have taken apart.

If it is blowing black oil out the purge and dripping oil/leaving a puddle, that is a little excessive...

I did a youtube vid on stripping and cleaning the old style dryers, username Rronmar...

 

[j_boucher]

oil contamin

The oil returns thru its connection to the timing case where he drive gear is located.

All compressors, like engines pass a certain amount of oil, a clogged intake/kinked hose can make this worse by deepening the vacuum during the intake stroke.

What are you considering "oil contamination" as that is one function of the dryer, to separate out this routine oil. If you pull it apart and you found yellowish oil/water emulsion paste, that is not uncommon, and have found it to some degree in every dryer I have taken apart.

If it is blowing black oil out the purge and dripping oil/leaving a puddle, that is a little excessive...

I did a youtube vid on stripping and cleaning the old style dryers, username Rronmar...

As always thanks for the info , I'm actually in the process today of swapping my dryer to the newer style , and governor as well "It was cheap" , while I'm doing all this I will also be changing the lines on the tank per your write up as mine an AO. When I said Oil contamination it is the yellowish paste, I don't have oil dripping and leaving a puddle but I do have the yellowish paste and the blowing black oil out the purge. Also there is no oil in any of the tanks. One another note I also thought of swapping the rigid line feeding the compressor with a flexible oil line, But im not understanding the size of the connectors in the TM Parts manual any know what size these are .? Thanks again

 

[GeneralDisorder]

You should at least rebuild the compressor cylinder head. Without exception, EVERY SINGLE ONE of these FMTV Haldex compressors I have opened up has broken exhaust valve springs. I came to this realization when the disc in one of my exhaust valves broke in half and slipped down into the cylinder - it punctured a hole in the compressor piston, scored up the cylinder wall, and beat the hell out of the head in that cylinder. I pulled the compressor but it ended up not even being rebuildable when the crankshaft broke trying to get the drive gear retaining nut off. I had to find a core to rebuild and get up and running again. Since that experience in 2021 I have opened up about five or six compressors and every one has had heat damaged exhaust valve springs that were broken into between 3 and 10 pieces and the discs have circles worn deeply into them from bouncing and rattling on the seat.

I carry a rebuilt cylinder head on board my truck as a spare after these experiences. It's only about $100 for the kit to rebuild them (includes the head gasket) and it's 6 bolts to swap it out on the truck. Takes maybe an hour tops. You are absolutely screwed if you have a failure like I had with a hole in a piston since that causes the compressor to push compressed air (under turbo-charger boost pressure) directly into the engine crankcase and it will blow oil out of the engine breather and likely cause other problems with gaskets and seals. Finding one of these compressors out in the field is very difficult - they are not the normal compressor spec'd by CAT. Those are only about 15 CFM. This is a military spec'd compressor that is 18 CFM - the assumption being the emergency mode of the CTIS system, and in general the military wants the air system to get the troops back from the field even with leaking hoses, etc. But you can't (easily) adapt something else in it's place since the power steering hydraulic pump is driven off the back and the support bracket is very specifically located and sized to run that exact pump - and without that brace you will crack the timing case as the entire weight of the compressor and hydraulic pump would be hanging off it by two bolt...... it's not something you want to deal with away from home. Thus my spare cylinder head and also monitoring wet tank inflation time at idle as a metric to ascertain compressor pumping efficiency and head-off any impending valve issues before they end in catastrophe.

The unloader piston o-rings also go hard/square and leak causing the unloader signal from the wet tank to leak wet tank air back through the unloaded intake valves. This is an insidious failure since it's invisible - the unload air signal leaks back into the engine intake.

In addition to ALL that - the new style Haldex PUREst dryer had a running change from a 150 psi relief valve to a 175 psi relief valve. I noticed that the 150 valve on mine would regularly open if I was under boost when the dryer purged. Partially due to it being spec'd too low and partially because my engine is juiced up to 370 HP and thus is running significantly higher boost pressure - and the compressor is fed air from the intake manifold post-intercooler where it's getting 30+ psi above atmospheric which is fed directly to the dryer when it unloads and the path between turbo and dryer is completely open.

 

[j_boucher]

You should at least rebuild the compressor cylinder head. Without exception, EVERY SINGLE ONE of these FMTV Haldex compressors I have opened up has broken exhaust valve springs. I came to this realization when the disc in one my exhaust valves broke in half and slipped down into the cylinder - it punctured a hole in the compressor piston, scored up the cylinder wall, and beat the hell out of the head in that cylinder. I pulled the compressor but it ended up not even being rebuildable when the crankshaft broke trying to get the drive gear retaining nut off. I had to find a core to rebuild and get up and running again. Since that experience in 2021 I have opened up about five or six compressors and every one has had heat damaged exhaust valve springs that were broken into between 3 and 10 pieces and the discs have circles worn deeply into them from bouncing and rattling on the seat.

I carry a rebuilt cylinder head on board my truck as a spare after these experiences. It's only about $100 for the kit to rebuild them (includes the head gasket) and it's 6 bolts to swap it out on the truck. Takes maybe an hour tops. You are absolutely screwed if you have a failure like I had with a hole in a piston since that causes the compressor to push compressed air (under turbo-charger boost pressure) directly into the engine crankcase and it will blow oil out of the engine breather and likely cause other problems with gaskets and seals. Finding one of these compressors out in the field is very difficult - they are not the normal compressor spec'd by CAT. Those are only about 15 CFM. This is a military spec'd compressor that is 18 CFM - the assumption being the emergency mode of the CTIS system, and in general the military wants the air system to get the troops back from the field even with leaking hoses, etc. But you can't (easily) adapt something else in it's place since the power steering hydraulic pump is driven off the back and the support bracket is very specifically located and sized to run that exact pump - and without that brace you will crack and timing cover case...... it's not something you want to deal with away from home. Thus my spare cylinder head and also monitoring wet tank inflation time at idle as a metric to ascertain compressor pumping efficiency and head-off any impending valve issues before they end in catastrophe.

The unloader piston o-rings also go hard/square and leak causing the unloader signal from the wet tank to leak wet tank air back through the unloaded intake valves.

In addition to ALL that - the new style Haldex PUREst dryer had a running change from a 150 psi relief valve to a 175 psi relief valve. I noticed that the 150 valve on mine would regularly open if I was under boost when the dryer purged. Partially due to it being spec'd too low and partially because my engine is juiced up to 370 HP and thus is running significantly higher boost pressure - and the compressor is fed air from the intake manifold post-intercooler where it's getting 30+ psi above atmospheric which is fed directly to the dryer when it unloads and the path between turbo and dryer is completely open.

I may seems easy enough / I did the unload er piston o rings yesterday I'm may research the part number for the head stuff kinda stuck until I can find the oil line elbow seems the "PO" hard cranked at an angle and stripped it ...ugh looking for a source for MS51504A4 ELBOW,PIPE TO TUBE..................

 

[GeneralDisorder]

I may seems easy enough / I did the unload er piston o rings yesterday I'm may research the part number for the head stuff kinda stuck until I can find the oil line elbow seems the "PO" hard cranked at an angle and stripped it ...ugh looking for a source for MS51504A4 ELBOW,PIPE TO TUBE..................

You have a picture? The oil line parts are all just off the shelf AN hardware AFAIK.

 

[GeneralDisorder]

Head rebuild kit is a Haldex RNT26

Haldex RNT26 Air Brake Compressor Gasket Kit + Cross Reference | FinditParts

Haldex RNT26 Air Brake Compressor Gasket Kit - Head Repair, For use on EL1300 / EL1600 / EL3200 Compressors ✓ Order now for same-day shipping on eligible purchases from FinditParts.com, America's online marketplace for heavy duty parts.

www.finditparts.com

 

[j_boucher]

You have a picture? The oil line parts are all just off the shelf AN hardware AFAIK.

Here you go

 

[Ronmar]

The A0 comp gets its air pre turbo so no added boost. The 150PSI relief on the dryer should be fine.

 

[MatthewWBailey]

Head rebuild kit is a Haldex RNT26

Haldex RNT26 Air Brake Compressor Gasket Kit + Cross Reference | FinditParts

Haldex RNT26 Air Brake Compressor Gasket Kit - Head Repair, For use on EL1300 / EL1600 / EL3200 Compressors ✓ Order now for same-day shipping on eligible purchases from FinditParts.com, America's online marketplace for heavy duty parts.

www.finditparts.com

$59 on eBay , "but only if you order today"!

 

[j_boucher]

So based on what I’m reading my compressor issues (minus the elbow for the oil) was it was cycling to much , sitting engine off the system holds air fine but going down the road I couldn’t understand it cycling like every 5-7 min I read somewhere on here that air could be feeding back to the compressor causing it to cycle more frequently / funny I replaced the unloader orings yesterday , I see the other kit has them as well so I guess I will have spares / I greatly appreciate all the masters help g me out

 

[j_boucher]

So seems I have some really bad exhaust springs

 

[GeneralDisorder]

Yep. Pretty much guaranteed nearly everyone on this forum has exhaust valve springs that look exactly like that. Except me of course.

 

[Ronmar]

I suspect you will still find leakage elsewhere. There is an output check valve on the air dryer, so once the air is pumped past that, there should be no going back to the compressor... If it is happening while driving, i would first inspect the park air lines, anti-compound valve and spring chambers. a park chamber leak would pass out thru the cage bolt holes. Depending on your year, you may also have a remote control valve inboard of the pri-sec tanks that disconnects air to the air/hydraulic pump when park air is applied.

Chock the wheels release the park brakes, a bad 2way could send park air out the front red glad-hand vent. Are the rear glad-hands capped/sealed? Fronts are vented, rears must be sealed...

 

[j_boucher]

Yep. Pretty much guaranteed nearly everyone on this forum has exhaust valve springs that look exactly like that. Except me of course.

Seems the makers would take better pride in their product and possibly have better parts those springs are pretty

I suspect you will still find leakage elsewhere. There is an output check valve on the air dryer, so once the air is pumped past that, there should be no going back to the compressor... If it is happening while driving, i would first inspect the park air lines, anti-compound valve and spring chambers. a park chamber leak would pass out thru the cage bolt holes. Depending on your year, you may also have a remote control valve inboard of the pri-sec tanks that disconnects air to the air/hydraulic pump when park air is applied.

Chock the wheels release the park brakes, a bad 2way could send park air out the front red glad-hand vent. Are the rear glad-hands capped/sealed? Fronts are vented, rears must be sealed...

i believe I’ve always heard the park air come out the back , but not 100%, I will check all items mentioned

 

[GeneralDisorder]

Wet tank air has to be continuously supplied to the unloader pistons to ensure the compressor stays unloaded till tank pressure drops below the governor set point - if the unloader piston o-rings leak then wet tank pressure will drop till the compressor reloads. Unloader piston leaks can cause short cycling of the compressor and you won't see any leaks since that air goes back through the compressor intake and into the engine intake post intercooler.

And yeah. The springs seem to be poorly designed but also short cycling due to air system leaks and back pressure due to insufficient dryer servicing or clogged desiccant from the compressor passing oil will overheat the springs and cause them to fail. In my experience basically EVERY truck has this problem and needs a cylinder head rebuild as one of the first services.

It's a vicious cycle. The more leaks you have, the higher the compressor duty cycle, the more it overheats the springs and unloader seals, the more it leaks, the more it cycles the compressor..... Etc etc. Till major failure stops the cycle.

 

[MatthewWBailey]

Wet tank air has to be continuously supplied to the unloader pistons to ensure the compressor stays unloaded till tank pressure drops below the governor set point - if the unloader piston o-rings leak then wet tank pressure will drop till the compressor reloads. Unloader piston leaks can cause short cycling of the compressor and you won't see any leaks since that air goes back through the compressor intake and into the engine intake post intercooler.

And yeah. The springs seem to be poorly designed but also short cycling due to air system leaks and back pressure due to insufficient dryer servicing or clogged desiccant from the compressor passing oil will overheat the springs and cause them to fail. In my experience basically EVERY truck has this problem and needs a cylinder head rebuild as one of the first services.

It's a vicious cycle. The more leaks you have, the higher the compressor duty cycle, the more it overheats the springs and unloader seals, the more it leaks, the more it cycles the compressor..... Etc etc. Till major failure stops the cycle.

Are the rebuild kit springs upgraded or the same type? I'm going to rebuild that old (now spare) compressor with one of those RNT26 kits. I put the new one in and it goes from 0 air to 120 in less than 3 minutes.

 

[GeneralDisorder]

Are the rebuild kit springs upgraded or the same type? I'm going to rebuild that old (now spare) compressor with one of those RNT26 kits. I put the new one in and it goes from 0 air to 120 in less than 3 minutes.

As far as I can tell the springs are the same type. The kits come with instructions that have been photocopied too many times..... I doubt any real thought has been put into this design in the last ~50 years. It's VERY old technology. I worked for a compressor repair and manufacturing company and rebuilt MANY Quincy recip compressors - quite a few were from the 1950's and 1960's (mind you this was about 2007) and came out of naval and coast guard ship applications, military bases, and tons of industrial applications. Be glad they used a disc valve compressor - much more long lasting and reliable than the consumer grade reed-valve crap that is used in every home depot and craftsman garage compressor. And *usually* doesn't result in catastrophic failure - of course my own example being the outlier in that regard. But that goes to show how much abuse our trucks lived with in their service life. My truck had 2,750 miles on it when I bought it. About 5,500 miles when the compressor failed. Come to find out the dryer cartridge was original from 2008

These perform fine when properly and timely serviced. They just never got that in their former life and they are often still overlooked in their current life.

 

[j_boucher]

So finished it up and took it for a good ride everything seems OK the gauge I put on the wet tank after the dryer purges sits at 110 PSI , dunno if that's the resting pressure after the dryer purges but I also installed a new governor and haven't made any adjustments and the CTIS works fine. so I guess its ok. I also noticed after about a 20 mile trip and items warmed up there was no more rattling coming from the compressor area.

 

[GeneralDisorder]

The governor should unload about 125 psi and reload at about 95 psi.

I've had better luck with Haldex governors than Bendix. FWIW. Most are adjustable but some of them they set and then used bolt cutters (?) to cut the adjustment rod threads and essentially lock the nuts in position. I hate that and refuse to put a non-adjustable governor on my truck..... but I'm a compressor snob after spending a few years in a compressor and pump rebuild shop.