Air Leak

Topic: Air Leak (Read 3355 times) previous topic - next topic

Re: Air Leak

Reply #50 – September 19, 2016, 09:42:37 am

Yes, the most common source for intake air for the air compressor on a diesel engine is the engine intake manifold.

But, easy to verify on any coach. Just trace the lines from the compressor. One will go to the source of air, the other to the air dryer.

So the air is filtered by the main air filter, the turbo boosts pressure and the CAC cools it. Gives the compressor a big jump on doing it's job.

Re: Air Leak

Reply #51 – September 19, 2016, 01:26:54 pm

Quote from: Chuck & Jeannie – September 19, 2016, 09:22:30 am

I just skimmed through the manual you linked. I'm trying to understand what the coach owner can do to avoid the situation you encountered. Being a typical owner, I never give any thought to "maintaining" my air compressor...it either works, or it doesn't. On our coaches, is the air going into the compressor being filtered by the big engine intake air filter? I ask because I have never actually investigated the flow of air into the compressor. Besides providing clean filtered air to the compressor inlet, and watching for leaks or unusual behavior, what else can the owner do?

Chuck,
"On our coaches"?
As you know, there are different compressors for different engines, depending upon OE manufacturer, year, size of engine, etc. and even then mounting configurations may well be different (D2 mounted directly on compressor or remotely, for instance).
For the 8.3 Cummins with Holset compressors, I posted a bit about this, trying to help Don (Acousticart) about 2 years ago. It's a bit more complex than just clean air in, demand (and leaks) going out. And there is not a wealth of built-in instrumentation to monitor compressor, D2 governor and air dryer normal/abnormal operation. However, the following may help in understanding a bit more about normal operation.

Air Dryer Rapid cycling?

HTH,
Neal

Re: Air Leak

Reply #52 – September 19, 2016, 02:14:45 pm

Chuck,

I would think the most important maintenance for the compressor would be air dryer maintenance. Moisture from the wet tank line to the governor would be a source if it's not dry. Also sitting up for long periods would allow for the rust and buildup to accumulate in the valves and their bores and cause them to stick. I don't think my air dryer was ever serviced and draining the tanks wouldn't be enough. We already saw the same problem with the one way check and protection valves on the tanks!

The advanced troubleshooting chart starting on page 13 will give all the info you need for maintenance on the 501. Look for rust, buildup, and kinks in the discharge line and soap test the compressor for air leaks. 60 psi is the minimum pressure required to unload. Recommended maximum inlet air temperature is 250F and discharge is 400F. A small shop air compressor with the correct fittings will help you test for leaks in the unloader, inlet, and discharge valves. Small leaks are acceptable. When I tested my unloaders not only were they not leaking they they were frozen shut! I had to use a pair of locking long nose pliers and a lot of effort to pull the valve stems out. After that the valves came out easily with some air pressure applied to the unloader port.

Jerry

Re: Air Leak

Reply #53 – September 19, 2016, 02:26:11 pm

See, this is what I love about this Forum and the many knowledgeable members - I learn something new almost every time I check in.

Thanks for the great link, Neal. I remember reading the first part of Don's ordeal with his mysterious air leak, but for some reason I missed your long and informative post concerning air compressor operation. Great stuff, and much to absorb (I learn by osmosis).

And thanks, Jerry, for bringing this whole subject to the attention of the group. I bet you have inspired more than one member to take a more active interest in their air compressor. I know i am going to continue to study the subject, and learn how to best take care of mine!

Re: Air Leak

Reply #54 – September 20, 2016, 11:41:36 am

Chuck,
Here's some pics of the discharge valves and springs and the field maintenance kit for the 501. The discharge valve seats were really tough to unscrew. I had to use a lot of PB blaster and 1/2" air impact wrench with a 14mm Hex bit to break them loose. You can see all the rust and buildup after 20+ years. They were working okay but I decided to replace the springs and valve plates with new ones. I'll clean up as much of the head as I can with brake cleaner before installing. The inlet valves will get new springs, valve guides and valve plates also. The maintenance kit OEM # 287043 or DMK-4410 contains all of the necessary parts and gaskets plus an unloader kit. Sure hope it makes a difference with all this effort and back strain on this old compressor!

Jerry

Re: Air Leak

Reply #55 – September 20, 2016, 11:48:59 am

Great photos! Be sure to add a final post to this thread when you get it all put back together and have had a chance to test it. Always nice to know the end result of these mechanical adventures.

Re: Air Leak

Reply #56 – September 25, 2016, 12:04:39 am

Chuck,
Looks like success!

I cleaned the compressor head up with some brake cleaner and emory cloth. Replaced discharge springs and valves and tightened them to 50 ft lbs. Painted the head with silver engine paint. I also cleaned off all the old gasket material on the compressor along with the the head and the inlet fitting. After tightening the 6 head bolts to 20 ft lbs. I tested the unloaders with my small compressor air pressure at the unloader port and they worked like they were supposed to!

I reconnected the inlet and discharge fittings. After those were in place I reconnected both coolant lines and the inlet and discharge hoses. I lost about 2 gallons of coolant and replaced that also. After reconnecting governor I started the engine and watched it build air to the cut-off psi and the unloaders worked to stop the compression. I know they were working because I wasn't fooled by the dryer purge blast. I had the dryer off and the by-pass hooked up.

After pumping the brakes about 5 times watching for compression between pumps, the cut-in pressure was reached and compressor loading started again and continued till cut-off. After trying this test about 5 times I was convinced the system was working properly.

I'll do some soap testing tomorrow on the fittings and put an air gauge on the governor at one of the reserve ports for wet tank pressure. I'll also do some testing on how quickly the system builds air and holds pressure overnight after the compressor service.

Jerry

Re: Air Leak

Reply #57 – September 25, 2016, 07:59:48 am

Great report, Jerry! You have blazed a path I hope I DON'T need to follow. (But if I do, I know it is "do-able").

Re: Air Leak

Reply #58 – October 21, 2016, 01:34:45 pm

Here's the compressor head installed after the maintenance work and soap testing. The gauge on the governor shows the pressure in the wet tank. Extensive soap testing so far shows no leaks.

I also removed the dryer and changed the filter, purge valve, discharge check valve, and seals. It's a Bendix AD-4 which is obsolete. You can still get parts and seals for it but there's no core allowance for it if you want to upgrade. When I took it apart I found one seal missing, two other seals broken and no discharge check valve! After cleaning, new seals, purge valve, o-ring, and filter, it works like new. The purge is much stronger and shorter in duration. I'm going to keep it for a backup and later upgrade to the much lighter spin on type AD-IP or Wabco 1200 like Pierce just installed on his rig.

Jerry

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Re: Air Leak

Reply #50 – September 19, 2016, 09:42:37 am

Re: Air Leak

Reply #51 – September 19, 2016, 01:26:54 pm

Re: Air Leak

Reply #52 – September 19, 2016, 02:14:45 pm

Re: Air Leak

Reply #53 – September 19, 2016, 02:26:11 pm

Re: Air Leak

Reply #54 – September 20, 2016, 11:41:36 am

Re: Air Leak

Reply #55 – September 20, 2016, 11:48:59 am

Re: Air Leak

Reply #56 – September 25, 2016, 12:04:39 am

Re: Air Leak

Reply #57 – September 25, 2016, 07:59:48 am

Re: Air Leak

Reply #58 – October 21, 2016, 01:34:45 pm

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