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    Liebert vacuum testing



    Searching for some help here...

    Working in an existing data center installing some new Liebert splits. 20 and 30 ton units. The owner has set our vacuum test procedures as follows...

    Step 1: pressure system to 160psi dry nitrogen. Hold for 1 hr.
    Step 2: pull vacuum to 1000 microns
    Step 3: break vacuum with dry nitrogen to 2psig
    Step 4: pull vacuum to 500 microns
    Step 5: break vacuum with dry nitrogen to 2psig
    Step 6: pull vacuum to 250 microns. Hold 250 microns with no more than 150 micron rise for 2hr minimum.

    This test is to be on the entire system (compressor, condenser coil, piping and evap. coil) all at once.

    Does this seem like a reasonable test procedure? We have about 100' of piping between the indoor unit and the condensing coil.

    The piping and condensing coil are pulling down and holding fine. We have been holding a 240ish micron vacuum for over a week now on one system. However, we are having complete hell pulling the indoor unit (compressor specificly) to just below 500 microns and holding. Changed the POE oil in one compressor and we can get it to hold 510-520 microns for 20-30 minutes. It has a steady rise of about 1 micron per 90 seconds. The other compressor has not pulled down to less than 400 microns yet. We have had a 10cfm vacuum pump on it for over 72 hours now with no avail. Mind you this is on the compressor only, valves are back seated fully.

    I have talked to another guy I know that works for Trane and he tells me that a 300 micron vacuum with 200 micron rise in 15 minutes is fine. This sounds much more reasonable.

    My questions I guess are:

    Is the owner being unreasonable in the testing requirements?

    Is the Trane testing procedure more realistic and achievable?



  2. #2
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    Re: Liebert vacuum testing

    Another question I forgot to ask...

    What could be preventing my vacuum test from reaching the 250 micron level?

    Other than the obvious leak.

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    Re: Liebert vacuum testing

    Procedure is wrong in first point.
    You should pressurize system (or part of system) to 160 psi and hold it at least 12 hr (24 preferably). You should record system temperature and correct your pressure change with temperature change (about 1.5 PSI with 1K change).
    Note pressures and temperatures after system is pressurized and after its temperatures are equalized (about 1 hr after pressurization) and at end of test. If you have leak, it will be shown.
    Also it is good to leave nitrogen bottle and pressure reducer valve connected while valve on bottle is closed and isolation valve on reducer (and any other between reducer and system) is open to system.
    In that way, smallest pressure loss in system (and connecting hoses) will be immediately noticeable on gauge witch measure bottle pressure.
    Look at that as error amplifier with amplification of factor which is equal to volume ratio of system and small volume between bottle and pressure reducer. That factor is pretty much big.

    http://www.refrigeration-engineer.co...ghlight=vacuum

    Also, don't forget that ordinary hoses are not designed to hold negative pressures and you should prefer to connect your micron gauge directly to system at opposite end from vacuum pump and to be able to isolate system in such way that no hoses are in game while micron gauge leak test is executed.
    You should use something like these:
    http://www.appioninc.com/products/vctfeatures.html


    Last edited by nike123; 23-09-2010 at 07:55 AM.
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    Re: Liebert vacuum testing

    Hi Guesstimator,

    160 psi sounds a bit light for a pressure test. What refrigerant are the units running on?
    I usually test R410a systems with 550 to 600 psi for at least 24hrs, better 48.

    sumsor

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    Re: Liebert vacuum testing

    Quote Originally Posted by sumsor View Post
    Hi Guesstimator,

    160 psi sounds a bit light for a pressure test. What refrigerant are the units running on?
    I usually test R410a systems with 550 to 600 psi for at least 24hrs, better 48.

    sumsor
    You cannot exceed system design pressure for long time.
    Some components are not designed to withstand highest pressure of system. As you know, compressors are usually having stated low and high pressure which cannot be exceeded. Sometimes, for example, low side cannot bare more than 11Bar (160 PSIG) of pressure.

    Last edited by nike123; 23-09-2010 at 10:08 AM.
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    Re: Liebert vacuum testing

    nike is being pretty much comprehensive.

    I just would like to add my 0,02. A steadily rising pressure after deep vacuum can also be evidence of refrigerant diluted in the oil. If the piping is new, and the unit is brand new, then it shouldn't be the case. Changing the oil is risky business in terms of moisture removal. If not done properly, it would entrain more moisture than remove.

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    Re: Liebert vacuum testing

    Now, when I am officialy citizen off EU, I am looking for decent job! For any job offer please check my profile!

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    Re: Liebert vacuum testing

    Quote Originally Posted by nike123 View Post
    You cannot exceed system design pressure for long time.
    Some components are not designed to withstand highest pressure of system. As you know, compressors are usually having stated low and high pressure which cannot be exceeded. Sometimes, for example, low side cannot bare more than 11Bar (160 PSIG) of pressure.

    Hi Nike,

    do you need to do two pressure tests in this case then? One only the pipework and indoor at high pressure and one for the wole system at low pressure?
    If R410a then 11 bar is way under the high pressure cut out of around 40bar or system running pressure in heating of around 28 bar.

    Sumsor

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    Re: Liebert vacuum testing

    Quote Originally Posted by sumsor View Post
    Hi Nike,

    do you need to do two pressure tests in this case then? One only the pipework and indoor at high pressure and one for the wole system at low pressure?
    Yes!

    If R410a then 11 bar is way under the high pressure cut out of around 40bar or system running pressure in heating of around 28 bar.

    Sumsor
    Usualy R410 systems are designed to bare with high pressures. Scroll compressor for R410 as Copeland ZP180KCE has low side pressure restricted to 29,5 Bar and high side pressure to 45. therefore you cannot pressure test it on low side with more than 29,5 Bar.
    Depending on other components in system, that could be even lower.
    Now, when I am officialy citizen off EU, I am looking for decent job! For any job offer please check my profile!

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    Re: Liebert vacuum testing

    Quote Originally Posted by guesstimator View Post
    Another question I forgot to ask...

    What could be preventing my vacuum test from reaching the 250 micron level?

    Other than the obvious leak.
    If temperature is high enough that could be evaporation of oil (as NNN already said). 500 micron end vacuum should be enough. If in few hours your level doesn't rise above 750 microns and it hold steady afterward, than you have dry and leak free system. Check diagram I posted before.
    Last edited by nike123; 23-09-2010 at 11:21 AM.
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    Re: Liebert vacuum testing

    This is a R407 system. I cannot put over 160 psi on the compressor itself because of manufacturer regulations. I have put 300 psi test on our piping and the condenser coil and it held for about 18 hrs. Our pressure test is holding fine on the entire system and we have soap bubble tested the entire unit and system with no leaks detected. We have, however, put a small amount of R407 in with the n2o and used a sniffer to find a leak and found nothing.

    The only problem we are having is the vacuum portion of the compressor. I can get my piping and the condenser coil to hold below 250 microns for well over 72 hrs. Also, the evaporator coil and piping will hold as well. The only thing that will not reach the 250 micron level and hold with the <150 micron rise over the 2 hr period is the compressor itself. I can achieve just below 400 but it does not hold the 150 in under 2 hrs.

    From looking at that graph, a 500 micron rise in 1/2 hr and then hold constitutes a dry tight system. Do I understand that correctly?

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    Re: Liebert vacuum testing

    You answered to yourself. You added R407 for leak testing (in EU it is forbidden), therefore you will never be able to evacuate the system, because R407 binds with the oil.
    You may want to try by heating the oil up and see if this helps.

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    Re: Liebert vacuum testing

    Quote Originally Posted by guesstimator View Post

    From looking at that graph, a 500 micron rise in 1/2 hr and then hold constitutes a dry tight system. Do I understand that correctly?
    Any (reasonable low) holding pressure for longer periods constitutes tight system. Level of holding vacuum tells you how much moisture you have in system.

    If you pressure tested compressor and it hold for 18 hours than your compressor is leak free.
    Last edited by nike123; 23-09-2010 at 05:51 PM.
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    Re: Liebert vacuum testing

    Quote Originally Posted by NoNickName View Post
    You answered to yourself. You added R407 for leak testing (in EU it is forbidden), therefore you will never be able to evacuate the system, because R407 binds with the oil.
    You may want to try by heating the oil up and see if this helps.
    I think that never is to strong word. It will evacuate it. It just need more time.
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    Re: Liebert vacuum testing

    I know this thread is a little out of date BUT what is the customer trying to achieve by breaking the vacuum twice and adding 2psi of OFN???

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    Re: Liebert vacuum testing

    Repeatedly breaking vacuum helps to move remained molecules of vaporised moisture toward vacuum pump during subsequent vacuuming.

    Check this video from 10:30
    http://www.youtube.com/user/HVACRat#p/u/10/qdv77SyBgKE

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    Re: Liebert vacuum testing

    Switch on crankcase heater while vacuuming
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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