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Pressure Quality of Air and Gas--What's the Difference??

03/27/2012 1:57 AM

This question quite intrigues me. Perhaps someone here could explain.

''What is the difference between gas pressure

and air pressure?? That is, you test Ammonia evaporating or condensing coils at, say 300 psi with gas, but you test the same at a lesser pressure , say 150 psi with air. Why??''

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#1

Re: Pressure Quality of Air and Gas--what's the difference??

03/27/2012 3:13 AM

Maybe you test in steps. First with air as long as the system in not commissoned yet. Later with the process liquid to the desired test pressure.

What does the manual say?

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#2
In reply to #1

Re: Pressure Quality of Air and Gas--what's the difference??

03/27/2012 3:25 AM

I know through practical experience as well as from manuals (such as by Sabro Denmark) that coils in a refrigerating system must be tested with almost half the pressure of air to check coil strength. This anomaly has been quite intriguing for me and I am unable to find a suitable answer to that. Even Mollier's chart didn't seem to help. Seems air properties are different than gas properties, understandable, it seems.

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#3

Re: Pressure Quality of Air and Gas--what's the difference??

03/27/2012 3:47 AM

So far this thread is nothing but mindless babble. After I count to ten overnight, maybe I will have a better answer tomorrow. Sheesh.

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#4
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Re: Pressure Quality of Air and Gas--what's the difference??

03/27/2012 4:15 AM

When you can't answer or find difficulty sleeping begin counting.......goes an old saying.

Surprising that someone should mark your reply as good....unfair. It's simply off topic.

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#5

Re: Pressure Quality of Air and Gas--what's the difference??

03/27/2012 7:04 AM

First off air is cheap. Second if there are repairs to be made like leaking joints anyone want to put a torch to it with Ammonia inside? So then you would have to flush the system to get all the ammonia out. Not so if you tested with air.

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#6
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Re: Pressure Quality of Air and Gas--what's the difference??

03/27/2012 10:06 AM

That could be one of the reasons but in practice there are different standards for gas and air pressure prescribed for testing the same coil which is perplexing.

Analogically, has anybody ever experienced the difference between pneumatic and air pressure while testing close-circuit tubes???

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#7
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Re: Pressure Quality of Air and Gas--what's the difference??

03/27/2012 10:10 AM

Of course not. Pneumatic pressure and air pressure are exactly the same thing.

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#8
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Re: Pressure Quality of Air and Gas--what's the difference??

03/27/2012 10:34 AM

I know 'pressure'' is 'pressure'' but why do we find stated anomaly in case of gas and air?? why lesser air pressure than gas (any gas) pressure is required for testing closed-circuit tubes???

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#9
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Re: Pressure Quality of Air and Gas--what's the difference??

03/27/2012 10:39 AM

See #5↑.

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#10
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Re: Pressure Quality of Air and Gas--what's the difference??

03/27/2012 10:49 AM

Thanks

seen but yet I am not sure ,,,that could be one of the reasons.

Will check out for further information ,,,

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#11
In reply to #8

Re: Pressure Quality of Air and Gas--what's the difference??

03/27/2012 11:09 AM

At 150 psi most of the plumbing problems will be found. Would you rather have a poorly sweated fitting blow out at you with 150 psi air or 150 psi ammonia or other gas that maybe hazardous. Now why not test with 300 psi air. I would think in a factory setting if possible they do if it save cost. How many 300 psi compressed air system you seen. Not that they are not available just most industry does not need that amount of air pressure. So you use what available and not as costly to provide. 150 psi works there in the field where the unit is.

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#12
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Re: Pressure Quality of Air and Gas--what's the difference??

03/27/2012 5:18 PM

In the present case the coil grid is all weld and made of schedule 40 or 80 steel pipe.

As for tubing its also all weld made of 26 SWG copper tubing

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#13
In reply to #11

Re: Pressure Quality of Air and Gas--what's the difference??

03/27/2012 9:22 PM

I'd go with this one as a complete answer to the second question!

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#14

Re: Pressure Quality of Air and Gas--What's the Difference??

03/28/2012 3:24 PM

Pressure testing and leak testing are two different things. Which test is being performed?

Molecular size and density are taken into consideration when testing parameters are scheduled.

Ammonia cannot be stored at lesser pressures or it will boil. Ammonia must be kept under high pressure for storage purposes...in your case 300 psi has been set.

Testing with air is for leaks only and does not determine the rating of the system. The rating of the material makes the determination.

The test report will still reflect that only 150 psi air was used.

Here is a good start

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