Air system problem

Bob & Tracey · October 02, 2012, 10:59:28 AM

Hi,

I am having trouble with my governor/air dryer (Bendix/Wabco). I noticed while going down the road the pressure gauge would occasionally read up to 150psi before the compressor unloaded. I replaced the governor and the compressor shuts off at 120psi but now I notice it takes a long time to build pressure, when the pressure is coming up and reaches about 100psi the purge valve begins to leak, at 120psi the compressor unloads and the leak at the purge valve continues until the pressure reaches about 100psi then stops when the compressor starts. This goes on while driving taking about 5 to 10 minutes to cycle. I replaced the purge valve with no change. I then reinstalled the old governor and adjusted it to unload at 120psi, I still have the leak at the purge valve but the leak stops (still about 100psi) before the governor starts the compressor so I do not have the cycling. Any thoughts?

Thanks,
Bob

gus · October 02, 2012, 02:50:16 PM

My 4107 did that for a few days about six months ago, it would only happen for the first 5-10 minutes after starting then go away. Weird!

Never did do anything about it!

Bob & Tracey · October 02, 2012, 03:34:09 PM

Gus,

I wouldn't care if the compressor wasn't running all the time.

gus · October 03, 2012, 07:18:06 PM

Bob,

The compressor runs all the time regardless, it just doesn't work under load when the pressure is up.

When my governor failed on my 4104 the pressure would build up to 150, gave me fits because I was sure something would blow on the ancient system. After installing the new gov it worked perfectly.

Dave5Cs · October 03, 2012, 07:30:35 PM

Bob sounds like what we just went through. I rebuilt the air dryer completely , takes about 1 hour. Your ball check valve is probably stuck open. It get divots in it and sticks closed sometimes and when the PSI is up it seems to seal but is open before that. It is included in the desiccant cartridge maintanance kit Napa heavy truck supplies 68.00 exchange. Also had to change out my PPV and change the type E air filter next to it in the front Bogie ceiling. HTH

Dave5Cs

buswarrior · October 03, 2012, 09:02:53 PM

What Dave5C said.

It is the unmaintained air drier causing troubles.

Do a preventive maintenance job on the air drier, and put your new governor back on.

Swap out all the bits with the big kit, strongly consider a new end plate with a fresh purge and heater and enjoy trouble free operation for a long time.

happy coaching!
buswarrior

Bob & Tracey · October 04, 2012, 08:44:51 AM

Dave5C,

Are you talking about the outlet check valve? I replaced the desiccant cartridge (NAPA) last year and there was no check valve with it. I am thinking of replacing the outlet check valve next.

buswarrior,

What do you mean "unmaintained"? There are some basic checks and replace the desiccant cartridge every 2-3 years. Am I missing something?

Bob

belfert · October 04, 2012, 09:23:17 AM

Purge valves on air dryers also need to be replaced/rebuilt on air dryers periodically in addition to replacing the desiccant cartridge.

Bob & Tracey · October 04, 2012, 09:41:58 AM

belfert,

I replaced the purge valve after I replace the governor.

Bob

buswarrior · October 05, 2012, 06:35:04 AM

What model of air drier do you have?

It is possible that the new purge valve is defective?

The whole unit may be corrupted somewhere and require replacement?

My comment about unmaintained describes the condition that many coach systems arrive into a busnut's hands.

It is rare for the last commercial operator to have done any air system maintenance, along with much else but run the coach into the ground.

Just about every busnut problem relates to something being far beyond its preventive maintenance schedule when we get it, and then we don't operate it daily for stuff to keep creaking into operation. Stuff goes wrong rapidly after that.

No offence was intended.

happy coaching!
buswarrior

Bob & Tracey · October 05, 2012, 07:29:30 AM

buswarrior,

No offense taken, I was wondering if there was something else I should be doing.

The air dryer is a Wabco System Saver 1200 new in 2003.

I don't think the new purge valve is bad because it is acting exactly the same as the old one, I think some other problem it causing it to do so. Going through the trouble shooting guide in the manual I feel the outlet check valve should be the next part to look at.

The previous owner pampered this bus mechanically, our issues have been mostly related to the conversion.

Thanks for your help,
Bob

Dave5Cs · October 05, 2012, 04:40:18 PM

Bob I have the AD2 so different, sorry. mine has a check valve on the top of the Cartridge with a ball valve there, it was stuck open.
Yes the in line should be replaced or rebuilt. It is just a little rubber ball and spring maybe an o ring. it should be the top hose to air dryer port in the big nut.

I also replaced my Pressure protection Valve 65 PSI 22.00 ceiling of the front bogie and right next to it is your type E filter. 4 bolts on the bottom corners and that comes down and the filter 3.40 drops out.

You might want to replace your compressors unloader pistons & spring, just get the unloader rebuild kit, 13.00
If you still have problems after that, then move to the rear axle area inversion valve, etc. Spray soapy water on all.
The 2 cap bolts on top of the compressor if take out there are 2 pieces of flat metal which over time get little circles pressed into them that don't allow them to close of the air fully and leak back through the compressor. If they have them on both sides it means somebody just flipped them over to save money and then they really should be replaced.
These are just some problem areas that relate to your problems that you might check , test, or replace. HTH

Dave5Cs

Bob & Tracey · October 18, 2012, 01:35:45 PM

I replaced the outlet check valve and that stopped the air from escaping through the purge valve but the compressor continues to cycle about every 3 to 5 minutes. The pressure reaches 120psi and as soon as the compressor unloads it begins to drop until about 100psi and then the compressor begins rebuilding the pressure. I can hear no leaks and the pressure holds when the engine is shut down.

luvrbus · October 18, 2012, 02:58:54 PM

Sounds like a bad unloader piston or o-rings on the unloader pistons are bad and it is just recycling inside the compressor

Bob & Tracey · May 16, 2013, 12:19:31 PM

I am back to working on this problem;

Compressor cycles every 50 seconds. If I shut the engine down after the compressor unloads the air will drop to about 100psi at the gauge and then stop. If I shut down before the compressor unloads the air pressure stays where it is.

I have replaced the;
governor
purge valve on the dryer
outlet check valve on the dryer
springs, pistons and o-rings on the unloader
air line from the governor to the air dryer

I have checked for leaks and can find none. If bus is aired up it takes 4 to 6 hrs before the rear bags begin to deflate, the front stays up for days.

Any thoughts?

Thanks,
Bob