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Author Topic: Air compressor  (Read 1800 times)
glang
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1998 Prevost XLT




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« on: May 27, 2006, 05:44:16 AM »

I recently installed a new (rebuilt) air compressor and Govenor (8V92). It is very very slow to build air, especially at idle. Works OK at highway speeds. Any ideas as to why? It is hooked up identical to the old one. The old one had broken valve pieces.

Gary
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TomC
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« Reply #1 on: May 27, 2006, 08:23:09 AM »

I had the same setup on my first truck and it did the same thing.  At least on my truck, the intake for the compressor was on the pressure side of the turbo.  When idling, or fast idling in the morning to build up air, it took sometimes close to 5 minutes.  But when going down the road, and especially when pulling a hill with full turbo boost, the pressure came right back up in a matter of a few seconds.  So long as the compressor isn't blowing oil and is doing the job (although slowly when standing still) it should be fine. Notice next time when driving when the compressor comes up (when you start to see the air gauges come up) then floor the gas pedal and see if the gauges come up much quicker, then your intake is on the pressure side of the turbo.  If you're engine savy, you could just look at the routing of the compressor intake and also figure it out.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Geoff
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« Reply #2 on: May 28, 2006, 04:35:09 AM »

It is normal for the air to build up slow when idling-- you have to use your foot or fast idle to get the air compressor to pump faster.  When you are driving the rpms are not only up, but you aren't trying to fill several empty tanks like you are when you first start.  BTW, Tom the air hose for the air compressor is supposed to be on the inlet side (air filter side) of the turbo, I have never heard or seen one on the outlet (pressure) side. 
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Geoff
'82 RTS AZ
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« Reply #3 on: May 28, 2006, 05:39:25 AM »

My 8V92TA DDEC is also on the pressure side of the turbo.

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Sojourner
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« Reply #4 on: May 28, 2006, 05:52:59 AM »

Gary is a great interesting friend of mine who is knowledgeable in rebuilding Provost from ground up and finish into a beautiful motorhome.
Another word he able to do about any if not all mechanical & electrical work.

His question is “why it take longer time to pump-up as to compare to before the replacement?”

He already knows that what being said…such as slow when idling & so on. Another word has anyone same experience he having?

My suggestion is might be bad rebuilt or smaller displacement than before.
1)   They do make difference internal version but same outside.
2)   Check valve in compressor is hanging up due to pieces of loose shaving of metal or some foringin material or improperly install valve from rebuilter.
3)   Intake hose collapse somewhat to restrict flow due to greater vacuum….old pump was tired. Usually installing a SS spring inside of inlet hose or replace for an reinforce hose. I have seen that happen because old soften hose. Collapse inside but OUTSIDE stay the same configuration…..you can only see that with vacuum gauge in between pump’s inlet to hose.
4)   Pieces of broken old pump’s valve parts got into next zone in air circuit such as check-valve or whatever blocking passage. Test by hook-up shop air to disconnected compressor line…to see if it fill up freely & quickly.

Good to hear from Gary on board!

Gary me e-mail if you will…JJ Image at Earthlink dot net…leave out the spaces & incorrect format.

FWIW
It Lord day to rest….oh sorry.
Sojourn for Christ, Jerry
« Last Edit: May 28, 2006, 05:56:52 AM by Sojourner » Logged
rv_safetyman
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Jim Shepherd


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« Reply #5 on: May 28, 2006, 07:29:44 AM »

As I had noted in a different thread, I recently attended a Bendix Air Brake School in Denver.  Great School and well worth the money.

They talked about the hose from the compressor to the air dryer becoming clogged with carbon.  The carbon was a result of oil passing and high temperature.

Might be worth your while to remove the hose (or in some cases tubing) and carefully run a wire (with rounded end) through just to make sure that you don't have some blockage.

From your description, I don't think that is the case.

Remember, that our buses have at least one more tank than a truck and lots of other "voids" (such as air bags) to fill up and that can take time.
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Jim Shepherd
Evergreen, CO
’85 Eagle 10/Series 60/Eaton AutoShift 10 speed transmission
Somewhere between a tin tent and a finished product
Bus Project details: http://beltguy.com/Bus_Project/busproject.htm
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Sammy
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« Reply #6 on: May 28, 2006, 08:09:42 AM »

As JIm has suggested, check the discharge line from your air compressor to the vey first fitting it will attach to.
It is very possible that it is restricted - blocked up with carbon.

As the compressors age, they pass very small amounts of oil into the discharge line.
The discharge line gets hot - from the compressed air, causing the oil to carbonize, creating the restriction or blockage.
You'd be amazed at how blocked up or restricted these discharge lines can become.
This is something I always check when replacing or servicing an air compressor, slow pumping complaint,etc.

i also recommend to service your air dryer at this time.
Check for restriction or blockage from that first fitting to air dryer assy too.
Don't forget to drain the air tanks - might have some contaminants in there too.

Best of luck with your repair.  Cool


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Geoff
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« Reply #7 on: May 29, 2006, 06:53:24 AM »

I wonder how much turbo boost is lost with the air compressor drawing air out the discharge side.  Not only that, but that air is HOT.  And if the turbo blows up metal will go into the air compressor. If my engine was set up like that, I would change it to before the turbo where it belongs.

--Geoff
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Geoff
'82 RTS AZ
rv_safetyman
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« Reply #8 on: May 29, 2006, 07:15:05 AM »

Hi Geoff.  My first thought when I learned about that plumbing option (compressor intake from turbo side) was the same as yours. 

Bendix prefers that installation from what I gather from my air brake school experience.  They don't like the stand alone filter, nor do the like the possible suction that can occur under full throttle when pulling air off the air cleaner to turbo line. 

Their compressors are rated for 250 degree incoming air.  I am a bit concerned about my installation, since I am having some air to air cooler issues (mounted on side opposite the radiator).  However, I should be able to keep it below the 250 degree level with some misting on the charge air cooler.

It turns out that most trucks are plumbed with the turbo inlet from what I can tell.

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Jim Shepherd
Evergreen, CO
’85 Eagle 10/Series 60/Eaton AutoShift 10 speed transmission
Somewhere between a tin tent and a finished product
Bus Project details: http://beltguy.com/Bus_Project/busproject.htm
Blog:  http://rvsafetyman.blogspot.com/
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