Liquid in suction of compressors

[maxmejia]

I have a rack with 3 copeland compressors and I keep controling the TXV, the Sorit valves, the liquid line valve, the suction pressure in the rack (is for -20°F), R-22 and still get liquid in suction line return. Any sugestions?

Regards,
Maxmejia

[Springbok]

How many evaporators/cabinets run off the rack?If a few,check all the tev's and make sure non of the evaporator coils are iced up.Just make sure if the orifices in the tev's are all correctly sized up....Hope it helps...maybe bit more info on the system could help..good luck!

[taz24]

I have a rack with 3 copeland compressors and I keep controling the TXV, the Sorit valves, the liquid line valve, the suction pressure in the rack (is for -20°F), R-22 and still get liquid in suction line return. Any sugestions?

Regards,
Maxmejia


You say you keep controling the TEV (txv) Why?

You need to go back a while.

How old is the system and how long has it ran?
When did the flooding start?
How many TEV's are there on the system?


You need to ensure the evaps are clear of ice and that all the evap fans are running correctly also check for the baffles in the air off ducts (if any)and check they are not constricted.

You need the think back to when it started to happen and then find what it is that has changed.

Check supperheats from individual evaps.
You should not need to adjust a valve once it has been set up correctly.

Go back to basics.

taz.

[US Iceman]

You need the think back to when it started to happen and then find what it is that has changed.


That is the best advice anyone could give, except this.... do not adjust expansion valves! Almost invariably adjusting expansion valves results in additional problems that can be difficult or time consuming to correct.

[monkey spanners]

What Symptoms make you think you are getting liquid into the suctions of the compressors?

[Refrigerologist]

Youi could have either a TXV that has 'gone wild' another problem I have had is a non return valve (check valve) that was installed in one of the display cases that was failing to seat. This was for a system using hot/cool gas defrost and would not apply if you have electric defrost heaters. The check valve was mounted between the luiquid and suction lines entering the case. On defrost cycle hot/cool saturated gas would enter down the suction line and be returned into the case liquid line to be desuperheated via the cases not in defrost. With check valve not seating, and the case demanding cooling, liquid refrigerant would pass directly into the evaporator suction line and return directly to the pack compressors.

[Refrigerologist]

That is the best advice anyone could give, except this.... do not adjust expansion valves! Almost invariably adjusting expansion valves results in additional problems that can be difficult or time consuming to correct.

A question! Why does everybody say never adjust an expansion valve?
Valves are factory set for a nominal set of operating conditions. If the coil/equipment does not meet these conditions, ie a freezer is completely different to a high tempererature vegetable cabinet, then the valve has to be adjusted. This is due to the differences in the diferential pressures between the liquid entering the valve and the suction pressure. Also is the liquid line rising or falling. This will make a difference due to gravity's effect on a column of liquid and its' pressure. TXV's should always be calibrated on site during commissioning. This ensure the best possible performance and the lowest operating cost!

[Chunk]

Not a lot of engineers are given the proper equipment to do their jobs and i damm well aint going to buy equipment that should be supplied by my company.
For example:thermometers.

I have always had to set up my txv`s the good old fashioned way: shut the valve totally and then reopen 2 and a half turns.

Until my company supply me with these futuristic tools i shall carry on with what i have been doing.:)

[NoNickName]

the valve has to be adjusted.


I quote that. TXV are there to be adjusted whenever they need to be adjusted. There's no thing such as a factory adjustment.
Almost invariably, TXV are never adjusted by manufacturers.

[nike123]

We don't say never adjust.
We say, once adjusted at commissioning, they should not be further adjusted for service purposes. On the other hand, if they are unadjusted they should be adjusted but, we must be sure that problem is with adjustment of valves and not with something else.
Is this sound OK?

[jumanje13]

hi all
it might be a moisture in txv that may restrict flow
what is the lp after and before

[US Iceman]

Nike 123 raised a good point. The valves should be checked for proper operation when the system is commissioned. And never adjusted again!

Too many people adjust TXV's to raise or lower the evaporating pressure, get more capacity, or just about any other issue you can name. People like to adjust these just as they like to add refrigerant because the system is not cooling. I realize these are beginners mistakes (even if the person has been doing this for awhile).

It can take some time to adjust only one valve on a system, without having to worry about multiple valves all being adjusted in the same time. Again, these are basic mistakes...but they keep happening.

If the TXV's are selected properly for the correct operating conditions they should account for any "rise or fall" of liquid lines or differential pressures for vegetable cases or freezer decks. These are application & selection issues, not field adjustments.

Based on my experience the only time I have adjusted a TXV is to correct the adjustment of someone else.

There is another RE member here who basically said the same thing I am saying (he works for a TXV manufacturer also;)). More problems are created by adjusting TXV's than what are solved in my opinion.



...we must be sure that problem is with adjustment of valves and not with something else.


I agree 100%. Unfortunately, people see adjusting stems and think they have to turn it.:D

[NoNickName]

Well, big manufacturers of mass-produced chillers adjust the TXV by number of turns before actually installing it and charge refrigerant by weight.
If everything is ok, then the TXV should not be adjusted, but if all manufacturing tolerances of components converge to the minimum allowed value or the maximum allowed value, all summed up the TXV adjustment is probably needed.

[US Iceman]

Well, big manufacturers of mass-produced chillers adjust the TXV by number of turns before actually installing it and charge refrigerant by weight.


I can't comment on that although I question why. The few manufacturers I have worked for used the factory settings (from the TXV manufacturer) for the TXV's and did not adjust them, nor recommend it.

Granted it has been some time since I have worked on commercial refrigeration equipment and there may be some new TXV's that require manual adjustment after the valve is installed. With the advent of some valves having changeable orifices, etc this may be the case. I can't say.

However, the majority of the TXV's I have used were Sporlan (both balanced and unbalanced ports) without the changeable orifices and I never had an occasion to have to change the factory setting during any system start up.

The few I have adjusted were on supermarkets with long lines on freezer cases where someone thought frost on a suction line was liquid slugging, so they closed the valves.:o Of course the frost disappeared but so did the temperature control of the display cases.:rolleyes:

So, my experience is... don't adjust valves unless you have very good reason. Of course then, someone thinks adjusting the valves to fix every "no cooling problem" is the answer, so that's why I say...don't adjust the TXV's, ever.

[Springbok]

Anyone know where mazmejia dissapeared to?He was the poster of the thread...:confused:

[nike123]

Well, big manufacturers of mass-produced chillers adjust the TXV by number of turns before actually installing it and charge refrigerant by weight.
If everything is ok, then the TXV should not be adjusted, but if all manufacturing tolerances of components converge to the minimum allowed value or the maximum allowed value, all summed up the TXV adjustment is probably needed.

That is why is properly performed startup procedure of equipment by qualified technician very important part of commissioning. When he make all necessary measurements and adjustments, further adjustment of TXV is no more necessary.

[Gary]

I have a rack with 3 copeland compressors and I keep controling the TXV, the Sorit valves, the liquid line valve, the suction pressure in the rack (is for -20°F), R-22 and still get liquid in suction line return. Any sugestions?

Regards,
Maxmejia

I see no reason to believe there is liquid in the suction line. Prove it... not for my benefit, but for yours. Show us the evidence.

[Kh1971]

Hi,

Please dont touch the exp valve , and try to check the evap and oil filters

[750 Valve]

maxmejia measure the pressure and temp back at the suction header and get back to us or we cannot help much.

Also does your system have suction/liquid heat exchangers at all? These have been known to let go on rare occasions

[jjthefridge]

I have a rack with 3 copeland compressors and I keep controling the TXV, the Sorit valves, the liquid line valve, the suction pressure in the rack (is for -20°F), R-22 and still get liquid in suction line return. Any sugestions?

Regards,
Maxmejia

Hi,

I'd go with the quote from taz, why even suggest adjusting valves, or checking orifices, I'd determine the case thats causing the problem, and pull it apart hopefully it'd be obvious, iced up, liquid line valve passing, fan motor gone. Controller lost defrost times, not defrosting long enough etc.

hope you find problem ok.

j.j.

[joe magee]

Don't forget to check the txv bulbs. They do come off. I do supermarket start ups and rarely do I need to adjust valves. Most of the ones I see come 4 turns open which is half way for these valves. They seem to run aprox 10 degrees super heat.:D

[Samarjit Sen]

Been pretty long in this field. Have always instructed my technicians never to touch the TEV. I take care in selecting the Valves. I have been using Danfoss or Sporlan. I have seen that with proper selection, there is never any problem. The problem may be lying some where else. There are so many components in a refrigeration system. If all these are not carefully designed, then problems starts. But certainly when the TEVs are once tampered, more problems starts.

It is very important that all the components which includes the piping as well should be carefully selected.

[Billy Ray]

I think this is a great debate,

Can i add my 10peneth worth...

Rather than tell your technicians not to adjust tev's..

Would it not be better to get in the van with them, go to site, pop on some gauges & thermometer at bulb location & analize the valve operation.

its no good trying to teach someone down the telephone line. Spend some time on site, & build peoples confidence.

Billy Ray..

p.s. I rarely adjust valves on site (cos they don't normallyneed adjusting), but i always check there operation.