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Topic: S/O Seal Air Tank Leak Only at Night - ???? (Read 674 times) previous topic - next topic

S/O Seal Air Tank Leak Only at Night - ????

Ok, I think I've gotten pretty good at finding leaks and fixing them.  I believed I had gotten the slide seal air tank fixed.  I added an isolation valve to close off the line to the HWH manifolds from the HWH compressor, so that only the seal tank, the seal vacuum manifolds, the air tank drain valve, and the seals themselves are connected (and the all the associated plumbing connected to the compressor).  Everything tested fine with soap solution.

So, here's the situation.

In the early morning I fill the tank to 105 psi.  When I check it some 16 hours later at bedtime, the gauge still reads 105 psi (and I know the compressor has not been on during the 16 hour period).  Then, at about 5 am, the compressor comes on.  If there was no air loss in 16 hours, how could there be some 20 psi of air loss in about 8 hours???  I've done this twice to show that it is reproducible.

My guess is that some fitting or valve gets cold and then leaks.  We're in southern California, so it doesn't get too cold at night - about 50F.

My plan of attack is to further isolate different parts of the system by disconnecting lines and plugging them.  I will, also, try spraying the fittings with refrigerant to cool them and see if they begin leaking.

Anybody else with suggestions?
Jim McNeece
2003 U320 40'
2017 Chevy Colorado Tow

Re: S/O Seal Air Tank Leak Only at Night - ????

Reply #1 –
Jim,
I've experienced the same effect but noticed it with the change of seasons.  It leaks the most in the cold of winter - exactly my least favorite time for crawling under the coach.
I theorized it might be due to the different coefficients of thermal expansion (CTE) between different materials in any given threaded joint.  Aluminum expands (or contracts) about twice as much as steel, and brass about 50% more than steel.  I can only suggest looking closely at dissimilar threaded joints where the steel has the female thread and spraying refrigerant on the male (non-steel) side to see the greatest effect.  The plastic DOT airlines have an even greater CTE but because they are sealed with a compression fitting, I don't know if the CTE has that much effect since the effect is on the wall thickness instead of the diameter.
I've also heard that commercial leak detection fluid works better than soapy water.  I've also heard that Bubble Blower for kids works better too.
John Fitzgerald
1991 U300 (SAI) Side Aisle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho

Re: S/O Seal Air Tank Leak Only at Night - ????

Reply #2 –
Greetings

NO EXPERT HERE, but i was thinking if air expands as it heats - wont it compress as it cools?

I don't know if its 20% but could it be possible? - again just asking :-)
The selected media item is not currently available.
My advice and experiences are Free, you decide if they are worth anything .

John - driving Old Faithful
1994 U280 GV
C8.3, Banks, Pacbrake, 900 watts, Resonator, XLHD tow dolly
Retired Army Warrant Officer

Life is what you make of it - if it is lemons, make lemonade!
Former Coaches:
1988 GV 40' ORED 300HP CAT - 9 years
1990 Winnebago LeSharo - 3 years
2000 Newmar London Aire - 3 years (#18 of 23 produced)

Re: S/O Seal Air Tank Leak Only at Night - ????

Reply #3 –
Quote from: fouroureye –
Greetings

NO EXPERT HERE, but i was thinking if air expands as it heats - wont it compress as it cools?

I don't know if its 20% but could it be possible? - again just asking :-)

NO. As a gas (including air) is warmed, the PSI goes up.  As it cools, PSI goes down. 

Not sure what you mean by a gas expanding (which suggests changing volume), as it is in a confined and unchanging volume system.

The Ideal Gas Law PV=nRT.  P is the absolute pressure of the gas, V is the volume of the gas, n is the amount of substance of gas (measured in moles), T is the absolute temperature of the gas and R is the ideal, or universal, gas constant.

Very simply with constant volume, rise in temperature causes rise in Pressure.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: S/O Seal Air Tank Leak Only at Night - ????

Reply #4 –
Brett - thanks

I was just thinking as a balloon,  like a tire heat makes it rise or expand, guess that is the pressure in your formulae.

Like I said, NO EXPERT, lol
The selected media item is not currently available.
My advice and experiences are Free, you decide if they are worth anything .

John - driving Old Faithful
1994 U280 GV
C8.3, Banks, Pacbrake, 900 watts, Resonator, XLHD tow dolly
Retired Army Warrant Officer

Life is what you make of it - if it is lemons, make lemonade!
Former Coaches:
1988 GV 40' ORED 300HP CAT - 9 years
1990 Winnebago LeSharo - 3 years
2000 Newmar London Aire - 3 years (#18 of 23 produced)

Re: S/O Seal Air Tank Leak Only at Night - ????

Reply #5 –
But...... metals  ( and adjoining sealing Ability) ) do expand and contract with temp.
1993 U300, 6v92
build 4366
USAF retired, Flight Engineer, C124, C130
 ATP, A & E.  & ex AI
 

Re: S/O Seal Air Tank Leak Only at Night - ????

Reply #6 –
Quote from: Bill Chaplin –
But...... metals  ( and adjoining sealing Ability) ) do expand and contract with temp.

Yup, many fittings leak more when cold.  Not only air, but also coolant, etc.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020