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Author Topic: Leak detection  (Read 3449 times)
wrench
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« Reply #15 on: December 21, 2008, 07:17:59 AM »

  & I like the idea of kid's soap!!!!!!!  man that poor guy out of Phoenix just lost a sale of BIG BLU stuff!!
Still have to try it!  should work good in a bind.
                  wrench
     

I was just thinking (ouch!) that if you let the bus completely run down so all the bags are deflated, then introduce R-134 as a gas into the compressor intake with the bus running, that it would get into every part of the air system with on oil introduced.  A leak detector might work quite well after all the gas has dissipated from around the compressor.

FWIW
Len

Len most of the guys I know who are GREAT at working on bus A/C systems use dry nitrogen to test for leaks because it is # 1 cheaper by far than 134, # 2 it is safer than 134 as it is a dry and "neutral" gas, which will not create problems with other types of gas, #3 they can charge it up to a fairly high pressure without having to run the system and still use a "sniffer" to detect leaks quickly and accurately!
Now with that said I have not heard of any of them trying this on a regular air system, but I guess it could work!

I always use the liquid bubble stuff sold in the toy department for kids to use for blowing bubbles. I put it in a spray bottle, and then I spray and spray away while the system is hooked to shop air! Once the bubble stuff hits the right spot you'll know it because it bubble like mad!

I do like the idea of trying smoke and will have to borrow a buddy's smoke machine to try it!
FWIW Grin  BK  Grin
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Len Silva
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« Reply #16 on: December 21, 2008, 07:27:02 AM »

It just seems to me that so many parts of a buses air system are inaccessible or hard to reach or see.  With a sniffer of some kind you could quickly get to the general area of the leak and then narrow it down further.  I didn't know that nitrogen would be detected  by a sniffer. 
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blue_goose
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« Reply #17 on: December 21, 2008, 08:15:17 AM »

The leak detector that Jack Conrad and I have check for air leaks not other gas.  Air leaks make a sound that most of us old people can't hear.  The leak detector hears them like a young kid.
Jack
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« Reply #18 on: December 21, 2008, 09:44:08 AM »

Len,

I think your 134 idea is great. Smiley  Hope that doesn't go against you. Grin  Those freon detectors will sniff out some really small and slow leaks.  Fool proof! 

I shudder to think of what that 134 oil would do to some of the rubber/plastic components in a bus system.  I don't think the oil would pass thru the first air tank.  Running the can with the top UP would keep all the oil in the can but most of the recharge stuff has no oil as I have read the label.  Great idea!

Wave guide?  AC&W Radar? 

John
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BG6
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« Reply #19 on: December 21, 2008, 10:47:23 AM »


What are you're thoughts on pressurizing the air system with R-134a and using a leak detector?


I think it's a bad idea.  Your seals are made for ambient air, not for a concentrated flourocarbon with other chemicals mixed in.

If it's a big enough leak, you could try pressurizing the system from a compressor that's far enough away so that you could hear the leak.  Another idea is to fill the air system with alcohol (as in your deicer fluid), then pressurize it and look for dripping.

Before doing that, I would seal off parts of the system and see which ones are NOT leaking, then dig into the one or two which are faulty.

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bobofthenorth
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« Reply #20 on: December 21, 2008, 11:18:11 AM »

I've also got an electronic leak detector on board.  Assuming we get out of Luke's shop and actually make it to Arcadia anybody who wants to is welcome to play with it as well.
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RichardEntrekin
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« Reply #21 on: December 21, 2008, 04:54:47 PM »

Ok, here are the results.

I used bulk 134a which does not contain any PAG or POE oils. The sniffer did go off on two known leaks that bubble quite slowly. So, the principle was proven to work. Since the high was 32 here today, with a healthy wind chill, I didn't spend all day playing with it.

Now, I used the aux air fitting to introduce the gas into the system, and in hindsight, I should have realized that pressuizes the brake tanks first. Next time I will break into the system at the auxiallary compressor and see if that works better. I only put about a pound into the system and used the engine compressor to bring it up to full pressure.

I like the idea of kid's soap bubble mixture. Thanks for that. And also thanks for the link on the "blue stuff" that the AC folks use.

My original idea was that I have many semi hidden connections and the leak detector would at least get me in the right area.

It was a fun experiment, except for the cold.

I spent most of the day playing with a laser level checking the alignment on the coach. I have an ever so slight pull to the right, and before I muck with cross caster to correct that, I wanted to make sure my thrust angles weren't off. It was pretty straight forward with laser. I made a jig to span the rim, and shot the laser to the front of the bus. Using a plumb I marked the spot about twenty feet in front of the coach. I crawled under and determined mid points of the front and rear axles and shot the laser from back to front, and again marked the spot on the concrete. It was simple then to take a tape measure and see if the measurement was equal from side to side. A lot of assumptions about true wheels, centered wheels, and what not were made, but the crude method showed 1/8 difference from one side to the other forty feet in front of the rear axle for both the drive and the tag. It was close enough that I won't worry about that as a factor.
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Richard Entrekin
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JohnEd
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« Reply #22 on: December 21, 2008, 05:40:47 PM »

Richards,

Thats great!  I think the 134 sniffer is the very best to detect a leak area.  Once you do that I think the bubbles are the next step to zero in on it.  I think you will get there faster using the sniffer and you will be able to scan lines and cavities.  How much did the freon sniffer cost or did you rent it?

Thank you, Len

John
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"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.
The price of apathy towards public affairs is to be ruled by evil men." Plato
“We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light.”
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RichardEntrekin
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« Reply #23 on: December 22, 2008, 07:18:35 AM »

I got it free when I bought a jug of r-22 to top off the House basement A/C units. Yes, I did have to get a license to buy it. It wasn't too hard to pass the test, but LOL I have a degree in Chemical Engineering, so maybe I should have passed. Cheesy
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Richard Entrekin
95 Newell, Detroit S 60
Subaru Outback toad
Huntington WV

Often wrong, but seldom in doubt
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