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09-09-2010, 08:01 PM #1
Intermittent flash gas in liquid line help.
Hello
Small cold room set point 5c holding at 6.5c
R22
Condenser on:26c Off:34c subcooling 6c (measured once only)
Evaporator on:7c Off: 5c superheat 12c (measured once only in wrong place)
LP 3.5 bar / -3c
HP 15 bar / 42c
Can anyone explain why the sight glass on this job is full for about five minutes, then flashes off by about 50% then slowly fills up again after 5 mins or so?
I don't want to replace TEV until i'm sure.
Any ideas anyone?
Thanks All
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09-09-2010, 08:12 PM #2
Re: Intermittent flash gas in liquid line help.
Sounds like the valve is hunting a bit, does the suction pressure go up and down a bit too?
I have a guide book by danfoss on setting up valves somewhere, but can't find it to check but i suspect it could be the orifice is too big.
Wait for more knowledgeable members opinions before a trip the wholesalers though
What was the reason for you attending the cold room?
Jon
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09-09-2010, 09:32 PM #3
Re: Intermittent flash gas in liquid line help.
Called out as room too warm, they want 4 degrees (dairy fridge).
Is it normal for the sight glass to empty when a valve is hunting or could this also be slightly short of gas?
Thanks
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09-09-2010, 10:44 PM #4
Re: Intermittent flash gas in liquid line help.
Could be that someone has adjusted the TEV out of range.
Sort fault finding from Sporlan here...
http://www.sporlanonline.com/Form10-143.pdf (260kb)Brian - Newton Abbot, Devon, UK
Retired March 2015
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10-09-2010, 12:13 AM #5
Re: Intermittent flash gas in liquid line help.
I would add refrigerant until the subcooling is about 8-8.5K, then take new readings.
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10-09-2010, 06:35 AM #6
Re: Intermittent flash gas in liquid line help.
it's a phenomena where your liquid is leaving your condenser at near 0 SC. On a log p/h graph, your left point on the condensing line is just on the saturated line.
When it starts flashing cover once fast your condenser with a piece of paper, you will see that the bubbles will disappear. Leave it there for 1 minute and then remove it, the bubbles will com back within 5 seconds.
Is the fan perhaps HP controlled?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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10-09-2010, 06:37 AM #7
Re: Intermittent flash gas in liquid line help.
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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10-09-2010, 06:38 AM #8
Re: Intermittent flash gas in liquid line help.
Is it an Unithé Hermétique group?
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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11-09-2010, 12:57 PM #9
Re: Intermittent flash gas in liquid line help.
It's a Unitie Hermetique with no fan speed control
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11-09-2010, 03:49 PM #10
Re: Intermittent flash gas in liquid line help.
Typically, A UH has no SC battery in its condenser coil.
Is your TEV sized not too bigIt'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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11-09-2010, 06:21 PM #11
Re: Intermittent flash gas in liquid line help.
It would be interesting to measure evap superheat & sight-glass response simultaneously. If they move together, then perhaps TXV hunting could be investigated.
Could the evap fans be hunting slightly, or even the condenser fan? In other words, something else is causing the system disturbance.Engineering Specialist - Cuprobraze, Nocolok, CD Technology
Rarefied Technologies ( SE Asia )
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12-09-2010, 02:23 AM #12
Re: Intermittent flash gas in liquid line help.
Possibly an undersized liquid line creating the hunting effect.
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12-09-2010, 06:21 AM #13
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12-09-2010, 07:32 PM #14
Re: Intermittent flash gas in liquid line help.
did they move the external unit for say a half meter and make a bend in the liquid pipe that narrows the pipe diam. someone pushed the pipes aside because the needed the space, ore it looks nicer that way, and reformed the pipes. i can go one for ever like this you now. in 35jr you see some strange things happening that they don't tell you straight away.
Ice
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12-09-2010, 09:28 PM #15
Re: Intermittent flash gas in liquid line help.
Last edited by Gary; 13-09-2010 at 02:41 AM.
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12-09-2010, 10:00 PM #16
Re: Intermittent flash gas in liquid line help.
I'm new to this unit but the customer says it's been working fine until now, there have been no recent changes.
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13-09-2010, 02:44 AM #17
Re: Intermittent flash gas in liquid line help.
Put a sightglass into liquid line at the TX valve, that will tell you what is entering the TX and creating the hunting effect. Plus re-check the evap superheat conditions. TX valves do go awol
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