Brake Air Compressor

[lonfu]

3126b cat on a FL chassis. Cat used a Midland 150-7638 air compressor with a serial # NT7028F 13 spline shaft with the hydraulic pump hanging off the back.

Looks like Hadex has bought out Midland now owned by the Fins. replaced air dryer and got oil and soot coming out out of the new dryer again.... Still getting plenty of air pressure but when it purges a huge mess on the toad....

Guessing the compressor seals have failed and the entire unit needs to be replaced. $2000. for the part. I can't even find a used unit to send off to a rebuilder.... anyone know a possible source for a used rebuildable unit???? anyone deal with this problem before?

[Alpine36]

Try Brake and Clutch Supply in Seattle. Very knowledgable bunch of old timers work there. If they can't help you out, nobody can.

https://brakeandclutchsupply.com/locations.shtml

[kenwyatt]

Lonfu, Didn’t I just see this unit on the classified for sale?

[lonfu]

Originally Posted by kenwyatt

Lonfu, Didn’t I just see this unit on the classified for sale?

yes, your correct, but i sold it in less than 12 days and it said the add expired in 14 days..... guess this is not true... marked it sold now...

[twinboat]

How often does your air dryer purge. Frequent purging means the compressor is running to much and possable overheating. That causes oil blowing past the piston rings.

They have a 25% duty cycle.

[lonfu]

Originally Posted by twinboat

How often does your air dryer purge. Frequent purging means the compressor is running to much and possable overheating. That causes oil blowing past the piston rings.

They have a 25% duty cycle.

My air compressor is splinned to the engine cam. It runs all the time, there is no clutch. The hydraulic pump that operates the fan and power steering is connected directly to the back of the pump and moves at the same speed as the pump. As the engine speeds up so do both the air compressor and hydraulic pumps. I've never timed the purge valve, but I did replace it when I replaced the air dryer and desicant filter.

[lonfu]

Doesn't anybody have any info to help out with the brake air compressor???

[KanzKran]

Originally Posted by lonfu

My air compressor is splinned to the engine cam. It runs all the time, there is no clutch. The hydraulic pump that operates the fan and power steering is connected directly to the back of the pump and moves at the same speed as the pump. As the engine speeds up so do both the air compressor and hydraulic pumps. I've never timed the purge valve, but I did replace it when I replaced the air dryer and desicant filter.

That's pretty standard. We have many larger Caterpillar engines where the compressor has a through-drive to the injector pump (older units). Obviously, it has to run at cam speed or it won't run.

But the compressors have a governor and an unloader valve, which results in the intake valve being held open when compressed air is not needed. It just sort of 'breathes', which requires little input power, and makes little heat, though the compressor is probably liquid cooled anyway. So the compressor spins all the time, but only does work when it's required to.

[lonfu]

Originally Posted by KanzKran

That's pretty standard. We have many larger Caterpillar engines where the compressor has a through-drive to the injector pump (older units). Obviously, it has to run at cam speed or it won't run.

But the compressors have a governor and an unloader valve, which results in the intake valve being held open when compressed air is not needed. It just sort of 'breathes', which requires little input power, and makes little heat, though the compressor is probably liquid cooled anyway. So the compressor spins all the time, but only does work when it's required to.

Ok, so found the compressor pump at Brake Systems Inc. in Portland Oregon. Have ordered one for a discount price of $1760.00 incl. ship and tax delivered to my door. Ow!!!!!!

50Lb old one is only good for a $100. core at Brake Systems as the one ordered is brand new. $450. to rebuild old one. Shipping makes the core worthless, guess I'll try to rebuild it when I have some time to fool around... I've rebuilt engines and such so why not a compressor.

I've never heard of a compressor with a governor before like that. I'm interested to pull apart the old one to see what it looks like. My Haldex air dryer has a valve that is replaceable that vents when the pressure hits a certain pressure to blow the moisture and oil out of the air dryer filter and to manage the top end air pressure, or so I thought.

Now to get the old unit out, it sits right next to the frame and looks like PIA to get out. Got a call into a local shop but they seem to be dragging their feet about getting me a quote. Looks to me that the hydraulic pump and compressor need to come out at the same time. gotta be about 75 pounds or so at least....
http://www.irv2.com/forums/attachmen...1&d=1575367099

http://www.irv2.com/forums/attachmen...1&d=1575367099

[twinboat]

All air compressors have a governor.

They control the purge of the air dryer and unloads the compressor by opening the intake valves at the same time.

A simple leak at the governor will cause the compressor to cycle frequently.

At idle, engine running, the air dryer shouldn't purge more often then every 10 minutes or so. And that's with some leaks.

Replacing the compressor may stop the oil discharge but not fix what caused it.

Search out Midlands or Bendix compressor troubleshooting guide for causes if your problem.

[KanzKran]

Originally Posted by lonfu

I've never heard of a compressor with a governor before like that. I'm interested to pull apart the old one to see what it looks like.

Compressors that stop spinning when air isn't needed don't have a governor, but they do have an unloader valve to bleed the air pressure off the cylinders for an 'unloaded' start when needed. But those that spin continuously, like on a truck engine, or larger stationary industrial compressors (piston and screw) use a governor that does what twinboat describes above, with some differences for stationary units. But same principle.

[lonfu]

Originally Posted by twinboat

All air compressors have a governor.

They control the purge of the air dryer and unloads the compressor by opening the intake valves at the same time.

A simple leak at the governor will cause the compressor to cycle frequently.

At idle, engine running, the air dryer shouldn't purge more often then every 10 minutes or so. And that's with some leaks.

Replacing the compressor may stop the oil discharge but not fix what caused it.

Search out Midlands or Bendix compressor troubleshooting guide for causes if your problem.

So, you must be talking about the little unit mounted on the side of the air compressor. looks to be about 2x5 inches and 2 air lines coming from it. I can see where this unit would "release air" good point, I'll look into it.

so, my air dryer fills up with oil and black soot. Black soot is most likely from the engine oil. The air dryer is doing it's job and purging every so often. I haven't timed it, but don't believe it is more often than you mention. I really notice it when I first start up, a big splatter of black goo and find it on my toad after just a couple of hundred miles.

When I looked at trouble shoot guides with my symptoms, they all pointed to the air compressor. As they age the seals leak and oil is drawn into the compression cylinders and blown into the air dryer and overwhelming it. Then the air dryer starts leaking the oil into the air tanks an so on down the line. I've replaced the air dryer and the "new $149 filter and desecant" unit is filled again with black goo after just a 600 mile trip.

My unit looks like the air compressor intake is taking the air directly from the crank case, I may be wrong about this can't seem to find any info that says other wise. It is possible that the air in the crank case could be contaminated so severely that it is ending up in my compressor but the engine has only 44k on it, so I tend to lean towards the compressor failure.

So, you are suggesting that somehow the air governor is causing the problem of oil getting into the air dryer? The air dryer is purging and the pressure gauges seem to be cycling 100 to 125 depending on the load of the brake and air bag system, I don't see how the air governor could be causing a problem.

Any one with some experience with this issue???

[twinboat]

If its not purging often, the next checks are the intake and discharge lines.

The compressor intake should be running to the engine intake manifold, not crank case, where it draws in clean air from the engine air filter.
Any intake restriction will cause it to draw past the compressor piston rings.

Pull the compressor intake line off and it should be clean.

Next is the discharge line. When air is compressed it creates heat. That can cause a carbon build-up. That restriction causes the compressor to run hot.

The line could also be linked causing the same issues.

I'm not saying your compressor doesn't need to be replaced but you do want to find what caused it to fail.

44,000 miles is a short life for a compressor.

[lonfu]

Originally Posted by twinboat

If its not purging often, the next checks are the intake and discharge lines.

The compressor intake should be running to the engine intake manifold, not crank case, where it draws in clean air from the engine air filter.
Any intake restriction will cause it to draw past the compressor piston rings.

Pull the compressor intake line off and it should be clean.

Next is the discharge line. When air is compressed it creates heat. That can cause a carbon build-up. That restriction causes the compressor to run hot.

The line could also be linked causing the same issues.

I'm not saying your compressor doesn't need to be replaced but you do want to find what caused it to fail.

44,000 miles is a short life for a compressor.

No kidding, a very short life..... Intake line is clean as a whistle, stuck a bore brush up the hose. Exhaust line is not kinked, no carbon build up but has lots of oil in it and air dryer filter is fills up and purges all over my toad and drips on my garage floor. I suspect the wiper rings on one of the piston cylinders has failed. Does not purge to often.