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  1. #1
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    bubles before expasion valve



    Hello,
    Some refrigerant system, I saw bubles before expansion valve. I thought that, before expansion valve refrigerant is in gas state , but sometimes I see bubles (somethimes , not continuously).
    What does it mean? It is good or bad or normal situation for the system?

    Regards



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    hello aygul,
    How do you know there are bubble before the expansion valve.
    Are you looking in a sightglass, if so this SHOULD !! be clear.
    There should be just liquid going to to expansion valve if the system is ok & therefore the sightglass should have just clear liquid in it, no bubbles.
    If bubbles are present in the sightglass it could indicate a few faults. probably the most common is lack of gas but DO NOT assume this just by the bubbles. Have you fitted gauges yet if so what ae the readings, is the condenser clear & fans OK, Same with the evap. Post some more details about what sort of system and what you have found and i'm sure people will help you out

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    Hello,

    In this system I think condenser and evaporator is working very well, because condensing temperature is approximately 45 C and evaporating temperature is apr. 2 C , ambient temperature is 29C.
    According to these values system is working very well. But sometimes (not very often) I saw bubles in sightglass before expansionvalve.

    In addition to that evaporator and condenser are air cooled.

    What is your comment? Is This situation normal or is there a problem in the system?...

    Thanks for your opinions...
    Regards

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    There is an old saying "If if isn't broke, don't fix it"
    The bubble's could just be present when the system is pumping down. At the end of the day, if it's working ok then don't worry about it.

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    if the system was on 404a u might see some bubbles because of the glide - but only with 11k+ of superheat i have seen this. often settles down after running for awhile, then no bubbles!
    Last edited by Bones; 25-11-2003 at 11:54 AM.
    "Old fridgies never die, they just run out of gas!"

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    when the system is charged just enough, you will see the bubbles in the sight glass now and than, this is normal and you dont have to add any refrigerant. but while you are watching it, take some time and clean the condenser and check on the edges of the fan blades for dirt.
    your system is fine.

    chemi

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    There might be generated some flash gas in the line due to pressure drop due to different height (if the liquid is not subcooled).
    JSJ

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    Hi
    bubble may be quite normal, just a function of the valve opening then again they may indicate something wrong.
    Temperatures and pressures at that point would help to determine this. I.e. what subcooling have we, what pressure drop in the line ect.
    Having said that if the sightglass is close enough to the TEV you will ocassionally see bubbles due to the rapid local reduction in pressure from the TEV opening causing the liquid to drop to a pressure at which it is no longer subcooled.
    Hope this helps. Regards. Andy

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    Re: bubles before expasion valve

    Quote Originally Posted by aygul
    Hello,
    Some refrigerant system, I saw bubles before expansion valve. I thought that, before expansion valve refrigerant is in gas state , but sometimes I see bubles (somethimes , not continuously).
    What does it mean? It is good or bad or normal situation for the system?

    Regards
    In the condenser the gas condenses to liquid. if there is no subcooling and in aircondesnors it is normal the liquid is at this point of boiling.
    so if there is any valve before the sight glass or a long line the pressure will drop a little and thuss the liquid will start boiling again.
    a liquid cooler can be used.
    we on ships have the liquid line always going thru the suction header so the liquid is cooled and the suction gas is heated so any liquid inside the suction will evaporate.
    also used is a liquid line inside the coolerroom so it will cool down.
    the expansion valves can not handle gas very good so please correct.

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    Re: bubles before expasion valve

    You cannot assume there is a problem with the charge of the system because of bubbles in the sight glass. Attach gauges and measure the temp of the liquid line as it leaves the condenser. Compare this to the temperature scale on the gauges. If the temerature of the liquid line is less than indicated on the gauge then the system is fine upto this point as you have sub cooled liquid leaving the condenser. I have seen bubbles in the sight glass for other reasons than the amount of charge. If there is a filter drier fitted to the system before the sight glass check the temperature of the liquid line before and after- a substantial change in temperature would point towards a blockage. If there is a problem with the amount of liquid entering the evaporator, a large superheat would result, but where the system has a TEV this controlds the amount of liquid at the evaporator inlet by regulating the superheat anyway. Best thing to do would be to start with the basics and systematically eliminate causes until the problem (if there is one ) is found.

    Regards
    James
    a problem shared is a problem halved

  11. #11
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    Re: bubles before expasion valve

    Aygul, If you have a blend you may see bubbles in the sight glass and as was said in traditional azeatropes there are all the reasons previously stated.Blends could show flashing for the same reasons, however, they can also flash when there is plenty of liquid in the receiver. In fact, liquid in the receiver could be causing the problem, particularly when when the equipment is in a hot environment. blend will come out of the condenser slightly sub cooled at a temp below the saturated temp.of the blend at the eisting hi side pressure. Yet when the sits in the receiver can "locally fractionate"or change composition slighty shifting the components into the vapor space of the receiver, this will effectively produce a sat liquid in the receiver at the same pressure you had before, which flashes when it hits the expanded volume of the sight glass, but not to be concerned because these bubbles will callapse when the blend gets into the tubing which feeds the valve and will operate just fine. Remember you have to ck the other system perameters such as pressures,superheat and amperage to confirm whether you have the right charge. Don't rely solely on the sight glass.
    cogito ergo sum
    Roger

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    Re: bubles before expasion valve

    Sight glasses are misleading, but they usually have a moisture indicator, which makes them borderline useful. Subcooling and superheat are what really matters.

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    Re: bubles before expasion valve

    I have to go with Gary on this one. The only thing that I would say is that the sight glass should be used as nothing more than an indication only. The way to know if the system is low on charge will be a high superheat and a lack of subcooling. If the subcooling is OK than it means that there is liquid leaving the condenser and something else should be suspected. If there is no temp difference along the liquid line then the capacity of the expansion device should be considered. If there is a temp difference then you have pre expansion, which could be caused by a number of things.
    Last edited by iceman007; 26-03-2004 at 06:41 PM.
    a problem shared is a problem halved

  14. #14
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    Re: bubles before expasion valve

    Iceman
    "a problem shared is a problem halved" does that mean that if we share with an infinate number of people we will get a final solution? lol
    Roger

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    Re: bubles before expasion valve

    Hi Roger

    A problem shared is a problem halved comes from an old saying. I suppose it means that if you have a problem to solve it can be made smaller and easier to find the solution by talking to others, sharing it and collectively finding the answer. Two heads (or in this case many heads) are better than one.
    The thing I have been wondering, forgive me if I've missed the point or sound ignorant is what does LOL mean ?

    Regards
    James
    a problem shared is a problem halved

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    Re: bubles before expasion valve

    Quote Originally Posted by iceman007
    what does LOL mean ?
    See http://www.ercomputers.com/acronym.html
    Prof Sporlan

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    Re: bubles before expasion valve

    Quote Originally Posted by Prof Sporlan
    PMJI,
    Hey most of us are MOTTS, but AFAIK,MOTAS.

    It was J/K
    TTFN

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    Re: bubles before expasion valve

    hi peter,

    are you ok, took me some time to see what its all about.
    there is no section for fridgy`s there, what a shame.

    TTYL

    chemi

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    Re: bubles before expasion valve

    Thanks alot Prof !
    a problem shared is a problem halved

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    Quote Originally Posted by iceman007
    Thanks alot Prof !
    ROFLMAO !!!!
    Prof Sporlan

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    Re: bubles before expasion valve

    Bubbles always intermittently occur in sight glasses of liquid lines prior to TEV with properly operating systems. The cause can be inferred by thinking of the whole system. Take the system as being stable at a particular instant in time, the TEV is in a fixed position for this instant in time and the superheat is correct at this instant. An instant later the superheat increases by a tiny fraction of a degree for some reason and the TEV opens very slightly to compensate and bring the superheat back to the correct setting. But what does this TEV movement do to the rest of the system. The valve opens slightly allowing more refrigerant flow through it behind the TEV there is then a pressure drop albeit small. This pressure drop results in a small amount of flash gas generated in the liquid line as the system compensates until balance is reached again. the reverse occurs when the valve moves closed. there is a small pressure increase behind the TEV and obviously no bubbles. This is not 'Hunting' just a natural function of the TEV as it continuously tries to maintain a constant superheat.

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    Re: bubles before expasion valve

    This pressure drop results in a small amount of flash gas generated in the liquid line as the system compensates until balance is reached again.
    Not true in general, especially in those cases where you have sufficient/enough subcooling.[/QUOTE]

  23. #23
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    Re: bubles before expasion valve

    or if the system it a little low of gas and if the load changes

  24. #24
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    Re: bubles before expasion valve

    Peter...pickey, pickey, pickey, but true

  25. #25
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    Talking Re: bubles before expasion valve

    OK I'll say something! Mechanical subcooling is often not well understood, sometimes thought to be "getting something for nothing." In actuality, mechanical subcooling is fairly easy to understand, but it does consume energy.

    Unfortunately, the significant benefits of mechanical subcooling are not always realized in actual installations. In some cases, energy use may actually be worse than if mechanical subcooling was not used. This loss of performance is commonly caused by a loss of subcooling between the machine room where the mechanical subcooling occurs and the refrigerated display case where the subcooled liquid is used.
    Subcooling can be lost through heat gain along the liquid line due to inadequate or deteriorated insulation, routing of lines through hot spaces, condensation of moisture from humid air on cold liquid lines, heat gain from return air in air conditioning trenches and pressure drop through the liquid line. To realize the full benefits of subcooling, it must be maintained all of the way to the display case.

  26. #26
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    Re: bubles before expasion valve

    This is normal with pressure activated fan cyleing with multiple fans.As RD said...If it ain't broke...

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    Re: bubles before expasion valve

    Hi!
    I'm totally new here...It's my first reply...
    Bubbles....nobody wrote about capacity stages. If a circuit doesn't run on full load (100%) the sightglass can "lie" a bit.
    Last edited by hiitsme; 18-09-2005 at 09:05 PM.

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    Re: bubles before expasion valve

    Hi itsme,
    Welcome to the board hope you enjoy your stay with us

    chillin.
    IF AT FIRST YOU DON`T SUCCEED.
    DESTROY ALL EVIDENCE THAT YOU TRIED!
    and go get a cuppa

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    Re: bubles before expasion valve

    Welcome among us "Hiitsme" , hope you enjoy your stay . . .
    How is budapest , is it cold this time of year ????

    cheers
    best regards
    Engineering, sciences, math, physics and my brain will generate "not responding " soon

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    Re: bubles before expasion valve

    Hi,botrous
    Thanks for the welcome! I found the forums on this site interesting so I've joined to learn and maybe help a bit if I can.
    It's the first chilly morning.This time of year somtimes I wish I were a hairdresser or cook or something inside .... disgusting weather outside, ice-cold tools and it's becoming worse and worse. The best part is evacuating big systems outside at -15*C during a smaller snowstorm (last year experience).

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    Re: bubles before expasion valve

    I like Budapest. It is a nice place, though it was over 10 years ago I was there so can't really remember much.
    Was a bit sozzled at the time!

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    Re: bubles before expasion valve

    The best part is evacuating big systems outside at -15*C during a smaller snowstorm (last year experience).
    Hiitsme , wouldn't the situation be better if you had a bottle of wine with you ???

    I've joined to learn and maybe help a bit if I can.
    That's what forum are made for
    Engineering, sciences, math, physics and my brain will generate "not responding " soon

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    Re: bubles before expasion valve

    I like Budapest. It is a nice place, though it was over 10 years ago I was there so can't really remember much. Was a bit sozzled at the time!
    So changed from east to west ????
    Engineering, sciences, math, physics and my brain will generate "not responding " soon

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    Re: bubles before expasion valve

    Quote Originally Posted by botrous
    Hiitsme , wouldn't the situation be better if you had a bottle of wine with you ???

    Yeah, but think again.... it was well below -10.... what could I do with it??? Reckon it'd be frozen. Licking wine sounds me a little weird....not mentioning the bl**dy bottle what does make a pretty challenge to lick it empty.

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    Re: bubles before expasion valve

    Hi hiitsme.
    Been to you city last year.
    Beautiful place, spent there a week.


    Chemi

  36. #36
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    Re: bubles before expasion valve

    Chemi,

    Budapest is pretty popular in this forum, isn't it? It's really ok but can be a bit boring after 30 years here. And it's totally in wrong place (I mean winter should be banned)

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    Re: bubles before expasion valve

    Yeah, but think again.... it was well below -10.... what could I do with it??? Reckon it'd be frozen. Licking wine sounds me a little weird....not mentioning the bl**dy bottle what does make a pretty challenge to lick it empty.
    Who said it will freeze ? it conyains almot 13% alcohol , so it will not freeze at - 15 C . . . if it does , the next time try Vodka
    Engineering, sciences, math, physics and my brain will generate "not responding " soon

  38. #38
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    Re: bubles before expasion valve

    If the bubbles are only intermittent you may in fact have no problem with the system. Assuming you have a simple system and the sight glass is just downstream of the thermal expansion valve then at the point in time that the expansion valve adjusts itself open slightly a small drop in pressure occurs, although not enough or for long enough for any field use gauge set to see. This drop in pressure is exactly what the thermal expansion valve does although here it is on a very small scale. The system has to acheive equilibrium after every valve change and the pressure drop means that the saturated liquid at this point has to cool slightly to acheive stability so a small amount of flash gas is generated, liquid turning to gas requires heat which lowers the liquid stream temperature slightly to regain system equilibrium. So if a small amount of bubbles passes the sight glass and then glass clears and stays clear for a while before the next flash of bubbles then probably OK.

    Quote Originally Posted by aygul
    Hello,
    Some refrigerant system, I saw bubles before expansion valve. I thought that, before expansion valve refrigerant is in gas state , but sometimes I see bubles (somethimes , not continuously).
    What does it mean? It is good or bad or normal situation for the system?

    Regards

  39. #39
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    Re: bubles before expasion valve

    Assuming you have a simple system and the sight glass is just downstream of the thermal expansion valve
    Do you mean just PRIOR to the expansion valve?

  40. #40
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    Re: bubles before expasion valve

    Sure did Frank late nights get us all especially when you find you have already responded once to a question hit the road for a month or so come back see the original post and think OK lets give the same answer

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    Re: bubles before expasion valve

    Make No Mistake The Bulb Goes On The Evap Outlet

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    Re: bubles before expasion valve

    Hi Adacus1

    I thought so. Seems like you are busy right now. Hope the pay reflects the effort

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    Re: bubles before expasion valve

    Quote Originally Posted by Bones
    if the system was on 404a u might see some bubbles because of the glide - but only with 11k+ of superheat i have seen this. often settles down after running for awhile, then no bubbles!
    404a isn't the only refrigerant with significant glide. There are other refrigerants that will behave the same way.

    Also, even a pure liquid will produce bubbles if the turbulance of the fluid flow is high enough. It has to do with the flow of the fluid causing small low pressure areas along the tube wall, and thus fluid vaporization. If the sight glass is near a tight radius elbow or other such fitting and the velocity is relatively high, I would expect a lot of turbulance and some bubbles in the sight glass, even in R-22 systems, because of turbulance from the fitting.

    In the water turbine design field this is called "cavitation" and is not a good thing because it causes the turbine blades to erode over time. They don't seem to talk about it much in the HVAC field, probably because most of the time a few gas bubbles don't matter in regular pipe flow.

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