Thanks, John, for the speedy reply.
That has just about cleared things up for me.
I don't think I have time left to hammer out an other question on here tonight. I'll be back.

 

Heat?! whats that.. it's too cold out to think about heat lol.

Whoops, I did made a boo-boo, totaly spaced out the heat thing. It would really throw you off for a second if you went back to check to see if you had a leak and actually had more pressure huh?

Also, many racing teams use nitrogen in their tires too for the same reasons aircraft do.

I know for the most part the answer to this question is only someones opinion, but what is the minimum time one should leave a pressure check or vacuum check on a system? I know it'll vary on the size of the system, but for the sake of argument lets say this is a average residential/commercial system, say around 100' of pipe or less.

*Edit*
After thinking some more... Yes nitrogen is inert, but there could still be some moisture in the system if you do the pressure check 1st before a vacuum. I guess for the truly anal retentive people (not like there's any around here), you'd do a quick pressure check (say 15-30 minutes), then pull a vacuum down to less than 500 microns and hold it for a few minutes to get out most or all of the moisture. Then break it with nitrogen. If you do the triple evac, you'd suck it down once more, break it one last time with nitrogen, let that one sit for how ever long (possibly as long as the answer to the above question). Then do the vacuum check for x ammount of time.

Phew, sounds like a lot of work!



[Edited by amickracing on 01-12-2005 at 11:13 PM]

 

ouote: Pressure in the atmosphere(absolute): 760,000 microns

I’m trying to understand
if I work with pressure using one unit of measurement psi. I come to a different conclusion.

if 1 psi = 57,715 microns then

200 psi = 10,343,000 microns and


500 microns = .00968 psi

14.7 PSI - .00968 psi = 14.69032 psi difference in pressure between the two environments.
I just don’t see the phenomenal pressure difference.

What am I missing? .

Svtti1234

 

What am I missing? .

quote: Pressure in the atmosphere(absolute): 760,000 microns
Pressure in the refrigeration circuit(absolute): 500 microns

So the difference in pressure between the two environments is: 759,500 mircons

And the difference expressed as a percentage is as follows:

760,000 microns / 500 microns = 1,520 or 152,000 %

In laymen’s terms this means that the pressure outside in the atmosphere is 1,520 times as much or 152,000 % as in the refrigeration circuit. Now that’s not a great pressure difference, that’s a phenomenal pressure different!
I’m trying to understand
if I work with pressure using one unit of measurement psi. I come to a different conclusion.

if 1 psi = 57,715 microns then

200 psi = 10,343,000 microns and


500 microns = .00968 psi

14.7 PSI - .00968 psi = 14.69032 psi difference in pressure between the two environments.
I just don’t see the phenomenal pressure difference.

What am I missing? .

Svtti1234

 

John,

Our disagreement is about: "What is a bigger pressure difference: atmospheric pressure and 500 vacuum or 200 psi pressure and atmosphere?”
First of all, the mistake is using psia in calculating pressure difference between atmosphere and pressurized system.
Psia should be used only when pressure is been compared with vacuum.
When pressurizing the system to 200 psi, we comparing it to
zero psi of atmospheric pressure.
Dividing 760 000 microns by 500 microns to show how much there is a difference between vacuum and atmospheric does not make sense.
You can not obtain 0 micron of vacuum because it is impossible. If you could, your math would not make sense.
With pressurized system to 200 psi I can not divide 200 by
zero for the same reason.
How about I take my unit to Colorado.
Now if I divide 200 psi by 0.01 psi of atmosphere (0.01 is hypothetical) my pressure would be 20 000 greater then atmospheric.
Does this make a sense?

John, I agree with you that micron reading is more accurate for
indicating pressure changes, then reading a manifold gauge with pressurized system.


[Edited by sigma on 01-13-2005 at 03:21 AM]

 

I'm trying to understand

quote:

Pressure in the atmosphere(absolute): 760,000 microns
Pressure in the refrigeration circuit(absolute): 500 microns

So the difference in pressure between the two environments is: 759,500 mircons

And the difference expressed as a percentage is as follows:

760,000 microns / 500 microns = 1,520 or 152,000 %

In laymen’s terms this means that the pressure outside in the atmosphere is 1,520 times as much or 152,000 % as in the refrigeration circuit. Now that’s not a great pressure difference, that’s a phenomenal pressure different!


200 psi = 10,343,000 microns
14.7 PSIA = 760,000 microns
1 psi = 57,715 microns
.00968 psi = 500 microns

If the pressure difference was so much greater at 500 micron than at 200psi pressure 1,520 times as much or 152,000 %



Wouldn’t we see imploding ac units ?

Svtti123

 

I'm trying to understand

quote
Pressure in the atmosphere(absolute): 760,000 microns
Pressure in the refrigeration circuit(absolute): 500 microns

So the difference in pressure between the two environments is: 759,500 mircons

And the difference expressed as a percentage is as follows:

760,000 microns / 500 microns = 1,520 or 152,000 %

In laymen’s terms this means that the pressure outside in the atmosphere is 1,520 times as much or 152,000 % as in the refrigeration circuit. Now that’s not a great pressure difference, that’s a phenomenal pressure different!

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

The pressure difference between the atmosphere and a perfect vacuum, if it could be achieved,
Could only be 14.7 psia or 760,000 microns. So the pressure difference can never be than greater than atmosphere pressure X 1 ??????

 

service freak

lets keep it simple. make sure vacuum pumps is good
new oil and good working pump, should pull down to 25
microns.by its self using micron gauge if system
cannot pull down to below 1000 microns
you have a leak. 500 to 1`000 microns moisture in system
blandoff at 450 microns rises 25 microns in 1 hour
system is tight make sure vacuum pump is big enough to
handle job.

 

unanswered questions from john

ok, airplanes and race cars use nitrogen because it is dry if you were to use a air compressor the air would contain moisture that moisture will expand when heated as in landing and racing. same principle with the new install question i would expect a slightly higher pressure that 200 maybe 202 or so because the system wasn't evacuated before the nitrogen was put in. so there is some moisture content in your brand new lineset. go john go!

 

Dear Glgto,

Regarding your previous post:

“ok, airplanes and race cars use nitrogen because it is dry if you were to use a air compressor the air would contain moisture that moisture will expand when heated as in landing and racing.”

Good answer…………. definitely on the right track, not quiet to the station yet, but given time and direction, I think you’ll make it.


“same principle with the new install question i would expect a slightly higher pressure that 200 maybe 202 or so because the system wasn't evacuated before the nitrogen was put in. so there is some moisture content in your brand new lineset. go john go!”

Again, good answer……now I won’t comment on this answer quiet yet because I only have a few answers to my questions and would like to give it a day or two more so more people can answer.

I’ll post my comments Saturday morning and maybe someone might want to debate my answers….but again….we’ll see Saturday morning. Thank you for participating in my survey.

Respectfully Submitted,
John J. Dalton

 

Dear Amickracing,

Regarding your previous post:

“*Edit*
After thinking some more... Yes nitrogen is inert, but there could still be some moisture in the system if you do the pressure check 1st before a vacuum. I guess for the truly anal retentive people (not like there's any around here), you'd do a quick pressure check (say 15-30 minutes), then pull a vacuum down to less than 500 microns and hold it for a few minutes to get out most or all of the moisture. Then break it with nitrogen. If you do the triple evac, you'd suck it down once more, break it one last time with nitrogen, let that one sit for how ever long (possibly as long as the answer to the above question). Then do the vacuum check for x ammount of time.

Phew, sounds like a lot of work!”

I’m not going to post my comments on my service scenario till Saturday morning in order to give more people a chance to answer my questions but I have to say one thing.

Maybe this will finally clarify the point I’ve been trying to make throughout the last few pages of this thread, the fact that a “hold test” whether it be a 500 micron vacuum test, or a 150-200 PSIG test IS NOT the FIRST test you make in your leak checking procedures, but rather the LAST TEST you make to simply VERIFY whether a leak is present or not. But again, we’ll see soon enough. Thank you for participating in my service survey regarding the hold test.

Respectfully Submitted,
John J. Dalton

 

Common Ground My Friend

Dear Sigma,

In regards to your post:

“John, I agree with you that micron reading is more accurate for
indicating pressure changes, then reading a manifold gauge with pressurized system.”

At least we have some common ground to start from. This theorem you requested will take some time and I know some of our readers will get board, but I will try to answer your concerns, questions, and disagreements this Saturday morning if you will be available, if not I’ll still post a some new information on what you are requesting and we can debate it further. Let me start today though in revealing some more common ground we both share, at least I hope we do.

The pressure difference as “expressed in pure delta P” is as follows:

Delta P1 < Delta P2

Delta P1 = 760,000 microns – 500 microns = 759,500 microns

Delta P2 = 200 PSIG – 0 PSIG = 200 PSIG

Yes…I do agree with you on this point, but…..this is not the point I was making in my previous post my friend. Hope to see you Saturday morning.

Respectfully Submitted,
John J. Dalton

 

Re: unanswered questions from john

ok, airplanes and race cars use nitrogen because it is dry if you were to use a air compressor the air would contain moisture that moisture will expand when heated as in landing and racing. same principle with the new install question i would expect a slightly higher pressure that 200 maybe 202 or so because the system wasn't evacuated before the nitrogen was put in. so there is some moisture content in your brand new lineset. go john go!

Kind of Airplanes use Nitrogen because it is more dense than air.

 

Re: I'm trying to understand

The pressure difference between the atmosphere and a perfect vacuum, if it could be achieved,
Could only be 14.7 psia or 760,000 microns.

This is exactly what I say. We also must compare
apples to apples and use psig for pressure difference
between pressurized system and atmosphere.

 

A Question to all here on this thread

A Question to all here on this thread

You come to work at 6:00 in the morning with hot coffee in hand because it’s 60 degrees outside, your first job is to pressure test a new 5 ton split system that you completed installation on last night, you decide to pressure test the system to 200 PSIG with nitrogen to play it safe and leave it for the day to verify you haven’t any leaks in the refrigeration system. You were extremely careful in all four(4) of your welds because the condensing unit is located on the ground around a corner about 100 feet from the furnace and coil in the attic. You leave and continue making your rounds around town, your busy because it’s a hot day, you return to check your refrigeration gauge set, you want to make it a quick stop because its 90 degrees outside and you want to go home for the day..

Now, here’s my two questions:

1. What pressures do you expect to see on your gauge set, barring you had no leaks?

2. Explain why you would expect to see these pressures.

Thank you for your anticipated response in answering my questions regarding this typical service call.

Respectfully Submitted,
John J. Dalton

////////////////////////////////////////////////////////////
My answer.


Nitrogen Pressure Testing

Calculate the expected pressure changes within a pressure tested system due to ambient temperature changes.
Old 60 degrees 200 psi
New 90 degrees 212.3865 psi

If your second pressure reading falls somewhere between the original and the new then your system is leak tight.



Why ?
1.Nitrogen has a very small pressure change at these temperature’s.

2.We never evacuated the system of air and moisture .If it were clean you would see less of a pressure change.. Moisture and air would account for the 12.3865 change in pressure.


Svtti123

 

nitrogen in tires

Benefits of Nitrogen Inflation in any tire
• Less inflation pressure loss
• Less inflation pressure fluctuation with heat
• Reduced wheel corrosion
• Longer tread life
• Improved retreadability

While both nitrogen and oxygen can
permeate rubber, nitrogen does it much
more slowly. It might take six months
to lose 2 psi with nitrogen, compared
to just a month with air.
And, nitrogen is far less reactive.
It doesn’t cause rust and corrosion on
steel or aluminum, and it doesn’t
degrade rubber.
Wheel surfaces stay smooth and
clean, rubber remains supple and resilient. Inflation
losses are minimized – and retreadability is enhanced.

Water vapor in compressed air acts as a
catalyst, accelerating rust and corrosion.
Water vapor also absorbs and holds
heat. And, when it changes from liquid to
vapor, water expands tremendously in volume.
So, tires inflated with wet air tend to run
hotter and fluctuate in pressure more. That’s
why racing tires, where fractions of a psi can
radically change handling, are inflated with dry nitrogen.

 

How long should

Guys,

It is obvious we have a few engineers here on rhe ol' web site, but please don't confuse lab quality nitrogen with the bottles you get from the supply house or welding shop. yes there is a major difference. The nitrogen from the supply house's stock is considered (dry) as long as the ppm of water is below 1500 and if you have ever read an oil sample report that's the equalivent of a (wet) system. Lab quality must have under 20 ppm of moisture, note the difference 1500 ppm of water as opposed to 20 ppm of moisture. You would know if you were using lab quality nitrogen as it cost about 7 times the cost of regular nitrogen as it must be refined and dehydrated so much more. If you think I'm joking try this little experiment. The next time you nitro-up a system put a dry eye sight glsss in line between your regulator and the system, don't be surprised at the color change.

 

Where for art there

No responses how surprising, so I'll justgo back to school and tell all those customers that I've done annuals over the last 20 years (same machines) That iI am wrong on my approach to vacuum 'cause HVAC-TALK says so.

 

Withdrawn

withdrawn

 

Im going to go rest...my brain hurts...sheww thats alota readin...

 

Guys,

It is obvious we have a few engineers here on rhe ol' web site, but please don't confuse lab quality nitrogen with the bottles you get from the supply house or welding shop. yes there is a major difference. The nitrogen from the supply house's stock is considered (dry) as long as the ppm of water is below 1500 and if you have ever read an oil sample report that's the equalivent of a (wet) system. Lab quality must have under 20 ppm of moisture, note the difference 1500 ppm of water as opposed to 20 ppm of moisture. You would know if you were using lab quality nitrogen as it cost about 7 times the cost of regular nitrogen as it must be refined and dehydrated so much more. If you think I'm joking try this little experiment. The next time you nitro-up a system put a dry eye sight glsss in line between your regulator and the system, don't be surprised at the color change.

So are we putting moisture in the system everytime we leak check with nitrogen, or run a nitrogen purge through a drier while we are brazing it in?

 

Filling automotive and aircraft tires[1] due to its inertness and lack of moisture or oxidative qualities, as opposed to air, though this is not necessary for consumer automobiles.[2][3]

http://en.wikipedia.org/wiki/Nitrogen

 

no, no, no, pressure testing is way to go.

John Dalton, (skip right to last paragraph for digest of this post)


I enjoy reading your interesting and well thought out posts, however, please allow me to disagree without being disagreeable. In short, I disagree with your supposition that , "...the 500 micron hold test is the “preferred test” of “educated technicians” ..." While I'm educated, I am by no means an experienced tech. Since I am next to worthless as a technician, please allow me to dispprove your supposition in lieu of any other useful information I can offer to this forum. lol.

For those of you that are sick of reading the math, just skip to the last paragraph for my clincher ending! It really says it all anyway, without the babble in between.

Here is the summary of your supposition, pasted here, just so were on the same tangent:

Perferred Vacuum Method: 760,000 microns / 500 microns = factor of 1,520 ( phenominal, as you say )
I Pressure Method: 200 PSIA / 14.7 PSIA = factor of 13 (rounded) ( inferior as you point out )

Lets restate the two equations in their factored form (i.e. 1520 and 13 being the factors)
1520 (factor) x 500 microns = 760,000 micron
13 (factor) x 14.7 PSIA = 200 PSIA

Lets make this even easier for everyone and restate the values in bare bones microns, instead of PSIA. Hence;
Vacuum 1,520 (factor) x 500 microns = 760,000 microns
Pressure 13 (factor) x 760,000 microns = 9,880,000 microns

The pressure difference between the inside and outside of the circuit might be a factor of 1,520 or even 3,000 (if you compared to 250 microns vacuum), or even a factor of billions if we used 0.000001 microns as our unit of measure, or even factors of trillions and giga-zillions, and tera-quads, as we approach perfect vacuum, ( I like Star Trek), but in all cases, the maximum difference will never be more than 760,000 microns, (more or less).

So 1520 x 500 microns, or 3040 x 250 microns , or 1,000,0000 x 0.00001 micron (whatever) , are all just another way to say essentially the same value, that is, 760,000 microns, more or less. Keep in mind that 1,000,000 times 1 millionth, is still equal to only 1. With your method, the larger your factor, the smaller the unit.

And of course, I claim that when it comes to the pressure test method, it's easy to see that a whopping 9,880,000 microns is a 10+ times greater actual pressure difference than a mere 760,000. Rounded out, 10 million, or 1 tenth of 1 million. Which is more? Factors, regardless of how infinately large, play absolutely no role in determining pressure differences in a circuit. With enought pressure, the copper line will explode, but in a perfect vacuum, with a factor of a million times 0...0001 microns, the copper line will not implode. Referring to factoring is a convenient way to convey the scope of differences to others when the absolute values are not known or too large or too small to be meaningful to the topic. The use of factoring can be misused intentional or accidentally in reporting, and should never replace actual values.

This reminds me of the way government reports put a spin on everything, such as; 'unemployment is down 10 percent...' (a factor of x (10). While that sounds optimistic, it is meaningless information. Unemployement could be down by 10 people or 100,000 people. Percentages and factors are a good way to skew reporting in someones favor since they ignore actual values, which are the real empirical evidence needed for calculations.

And lastly, as indisputable evidence, with your vacuum method, a vacuum of only a mere 50,000 microns (barely a vacuum at all ), will have a factor of 14 ! (760,000 / 50,000 = 14) And since 14 is higher than the factor of 13 that we get with 200 psi of pressure, then your suggesting that even a light vacuum is superior to high pressure testing. Do you think that a weak vacuum of 50,000 microns is a better leak test than 200 psi? Just a rhetorical question. I rest my case, your honor.
I submit this argument with all due respect, and I'm sorry that I am poor at injecting humor into my posts, as I see everyone else is so good at.