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    TXV's To Adjust or Not to Adjust - That is ....

    Many engineers' in this industry say "you should never adjust a TXV superheat setting as they are factory set".

    I would welcome comments on this statement.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    I have to because my commissioning engineers dont have time to, due to quick turnaround on jobs.

    It just means i have more time to play around when they dont.

    I work on supermarket packs so its not too critical what they are set to as long as the cases work.
    If it ain't broke, it doesn't have enough features yet.


    Damo

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by chunky munkey View Post
    I have to because my commissioning engineers dont have time to, due to quick turnaround on jobs.
    ......
    Now thats a frightening statement.

    If the commissioning staff are not allowed sufficient time to perform their task properly then they have not commissioned the job, merely turned it on.

    This is either due to the customer not wanting to pay for a proper job or the installing company trying to save a buck.
    Brian - Newton Abbot, Devon, UK
    Retired March 2015

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by powell
    The operating superheat setting for a refrigeration system depends on the temperature difference between the refrigerant and the medium being cooled.
    Aha! Now we are getting down to the real basics.

    You cannot get more evaporator superheat than you have temperature difference between the entering air temperature and the saturated evaporating temperature. Probably a few degrees less to be more accurate!

    This is hardly ever considered and I suspect we will get a lot of questions about this.

    If you only have 10°F (5.5°K) of temperature difference, the maximum evaporator superheat you can get is 10°F (5.5°K) in theory. 8 to 9°F (4.4 to 5.0°K) is probably the best you can get.

    Therefore, if someone tells you they have the valve set for 15°F (8.3°K) of superheat, ask them to prove it!
    If all else fails, ask for help.


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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by taz24
    They are pre set to about 6k superheat.
    For 95% of all applications you do not need to touch them.
    Only on rare occasions do you need to adjust.

    If the valve and orifice are sized correctly then there is no need to adjust, from experience the problems occur when there is a miss match in valve, evap and system design.
    I agree with taz. Except for the part about ouch them.

    If the valves are properly selected for the installed application, then by all means check the superheat. I think you will find they are pretty darn accurate with the factory setting.

    I think I may have started this by saying don't adjust the TXV's. I will stand by that comment.

    In practice what I mean is don't try adjusting the valve on a service call. It either works or does not. If it has failed then change it.

    Too many people adjust these to get some desired effect such as higher or lower suction pressure, trying to get rid of bubbles in a site glass, or heaven knows what else.

    When you truly do have to adjust a TXV it is usually because someone else was there adjusting it before you.
    If all else fails, ask for help.


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    Re: TXV's To Adjust or Not to Adjust - That is ....

    I DO adjust expansion valves. ONCE.
    If I am called to a plant with a over or underfeed condition, I will adjust expansion valves. ONCE.
    If they do not maintain their setting-change them.
    Mostly an NH3 guy, I find the factory seting on TX valves is usually not correct.
    But if have to adjust them more than once, there is a problem.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by US Iceman View Post
    I agree with taz. Except for the part about ouch them.

    When you truly do have to adjust a TXV it is usually because someone else was there adjusting it before you.

    The Ouch feeling when working with TEV's (TXV)


    Thats when you lose your temper with them and want to beat the c**p out of them with a spanner.

    taz.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    [quote=US Iceman;96656]Aha! Now we are getting down to the real basics.

    You cannot get more evaporator superheat than you have temperature difference between the entering air temperature and the saturated evaporating temperature. . . Therefore, if someone tells you they have the valve set for 15°F (8.3°K) of superheat, ask them to prove it!

    Oh that wonderful word "superheat" just how it evokes a discussion.

    Maybe we should first all agree to the definition of superheat and what it actually is? Because I'll bet my new digital gauges that we get more than one answer to this question.

    Who wants to start?

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    [quote=nevgee;110646]
    Quote Originally Posted by US Iceman View Post
    Aha! Now we are getting down to the real basics.

    You cannot get more evaporator superheat than you have temperature difference between the entering air temperature and the saturated evaporating temperature. . . Therefore, if someone tells you they have the valve set for 15°F (8.3°K) of superheat, ask them to prove it!

    Oh that wonderful word "superheat" just how it evokes a discussion.

    Maybe we should first all agree to the definition of superheat and what it actually is? Because I'll bet my new digital gauges that we get more than one answer to this question.

    Who wants to start?

    OK I'll bite
    To measure evaporator superheat:
    1) Record the actual temperature at the TXV bulb.
    2) Record the evaporating pressure at the TXV bulb.
    3) Convert the evaporating pressure to temperature by using those handy pocket pressure/temperature cards. These cards/charts show the saturation pressure/temperature relationship for those refrigerants.
    4) Subtract the temperature you converted on the pressure/temperature card from the actual temperature you recorded at the TXV bulb.
    5) The difference is the actual evaporator superheat

    as you can see this is a copy and paste, the thing that is not mentioned in this is the swing you get as your TXV opens and closes with demand. It takes time to set a valve properly you have to watch the case and use your lowest temp reading and check your pressure on that swing. If you have electronic SORIT valves your pressure also changes with demand.

    To set the valves properly takes time. And to answer the begining of this thread. YES every valve should be checked for proper superheat before a store is turned over.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by Brian_UK View Post
    Now thats a frightening statement.

    If the commissioning staff are not allowed sufficient time to perform their task properly then they have not commissioned the job, merely turned it on.

    This is either due to the customer not wanting to pay for a proper job or the installing company trying to save a buck.
    Hi Brian.

    Just to give you a picture of what goes on.

    We do a shutdown when the store shuts at say 10pm then case fitters come in and rip everything out.By 6am new cases in.Pack goes on vac for a day,gas is put in and cases turned on.Then we can setup controllers and get cases down to temp.

    Within 2 hours of cases being turned on the store is loading cases whether they are working or not,this is where the problem occurrs.

    One commissioning engineer per site having to set all case and pack controllers running comms and getting it all connected to monitoring system and only given 3 or 4 days to do this.

    All i can say is it is not like the old days when stores actually shut for a week so all work can be done efficiently,but this is how these supermarkets want to play nowadays.
    If it ain't broke, it doesn't have enough features yet.


    Damo

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    My main point would be: If expansion valves are not to be adjusted, why then does the manufacturer bother to fit an adjustment screw?

    Each installation is different. The liquid line pressure will vary from system to system even when operating at the same condensing and evaporating conditions. An evpaporator installed 20metres above the condensing unit will not have the same valve inlet liquid pressure with an evaporator installed 20 metres below the condensing unit. The same type of valve may have been installed. But the capacity of each valve will vary slightly due to the variance in diferrential pressure alone. This doesn't take into account a systems that use the same valve and orifice but the evaporating temperure for one is -36C and the other 5 C.
    I agree that in an ideal world, after the commissioning engineer has checked and set the superheat, there should be no need to fiddle with it. Unfortunatley, I have met & worked with quite a few 'engineers' (trained monkeys could have been as useful), who have no idea what superheat is, let alone how to check it!
    Last edited by Refrigerologist; 11-03-2008 at 09:07 PM.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by Refrigerologist View Post
    Many engineers' in this industry say "you should never adjust a TXV superheat setting as they are factory set".

    I would welcome comments on this statement.

    They are pre set to about 6k superheat.
    For 95% of all aplications you do not need to ouch them.
    Only on rare occasions do you need to adjust.

    If the valve and orrifice are sized correctly then there is no need to adjust, from experience the problems occur when there is a miss match in valve, evap and system design.

    taz.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Refrigerologist.

    The statement "never adjust a TXV factory superheat setting" reads in my mind as NOT checking superheat. Just install, charge and move on.

    The operating superheat setting for a refrigeration system depends on the temperature difference between the refrigerant and the medium being cooled.

    A newly installed, properly sized TXV's SH should be checked and then fined tuned if needed.

    Here's a link to the Parker/Sporlan (Sparker) website for more detailed info on adjusting superheat.

    http://www.parker.com/literature/Lit...20010/10-9.pdf
    Last edited by powell; 11-03-2008 at 01:33 AM.

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    Question Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by powell View Post
    ....
    Here's a link to the Parker/Sporlan (Sparker) website for more detailed info on adjusting superheat....
    I'm not sure that a "newby" should be posting in this older thread, but (unfortunately) that link has gone "404". I do see wonderful Threads on this BBoard, which probably provide even better information... but is that Sporlan PDF still available anywhere else? Meanwhile- I have question, and it's exactly this topic: "TXV, stay with factory-provided non-adjustable, or replace it with an Adjustable, sized smaller to match compressor?"

    Here's my sad history. I'm in USA, a homeowner with pretty much a new installation. (R410A) It's "pretty much new" due to a tech from a now-fired company trying to fix hunting and inadequate cooling, on a second call-back, by adding more charge, and more charge, and more charge... And it all blew up after he left. (Probably the Evap first, but the Compressor quickly followed.) Now to the point and question: I'm definitely not DIY, and my new tech (new company) seems way more competent. But I think that my configuration DOES call for upgrade of the factory-installed TXV to an adjustable, smaller sized TXV for several reasons:

    • The Evaporator Coil (from USA company 'Advanced Distributor Products') is oversized relative to compressor (17.5 kW versus 12.25 kW), for efficiency reasons.
    • altitude 5200 ft (yes, WAY up).
    • lineset > 50 ft, with about seven 90 degree turns (some "sharp", others "soft").

    ADP supplies this Evaporator Coil with an R410a TXV. It's a nonadjustable Emerson, the older Type-A, not the brand new Type-C. (So it's == Alco, IIRC.) Factory labels the part to be nominally capable of anything from 12.25 kW (42,000 BTUH) to the full Evaporator rating of 17.5 kW (60,000 BTUH). My Trane compressor is labeled at the absolute bottom of this range.
    So, I'm thinking that the TXV had better be operating nearly closed most of the time.

    And I don't like that idea, or the thought of it maybe trying to open up so wide as to generate bubbles in the incoming liquid line (from the less capable compressor). I saw severe hunting before, after the first recharge... although other service errors, including crud left in the lines, may have played a role at that time too.

    The only way to tune this one-size-fits-all Emerson is by adding or removing charge. (subcooling OR superheat, not both). And the flowrate "curve" is probably too "steep" anyway.) So I'm inclined to buy a Danfoss TR6 "universal upgrade" kit for him to swap in, before doing the final N2 blow-out and charging. Nominal size 4 tons (14.0 kW). Although some of you say that Danfoss makes 'em a lot "bigger" than the BTUH rating, I think that this would still be a better match for the 12.25 kW compressor than the factory-provided Emerson. (And even if the slope is still too "steep", at least some adjustment can be done via spring tension.) Should I maybe buy the Danfoss kit all the way down at "3 tons" nominal size?

    The one thing I won't like to do to the new guy is to make him charge it up, run, and test using the factory provided Emerson-- then find that I'm HATING the performance measurements, make him recover it all, then replace the TXV, then re-do the vacuum test and blow out with N2 (again) and re-vacuum (again), initial charge up (again), stabilize for measurements and charge adjustment (again), make changes, wait for it to stabilize (again) ... not a good way to win friends. So I'm inclined to ask him to take it out, replace it with the Danfoss right at the start of the call. BTW, Trane also discontinued the "factory authorized service" relationship with my original installers, and my "new" guys are Trane's current representatives here.

    Thanks for reading all this. BTW, it's A/C only (not a Heat pump), and outdoor temps here in Reno do exceed 100F (several times each year). But humidity is extremely low, all I need is the cooling.

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    Re: TXV's To Adjust or Not to Adjust - That is ....


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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by rickst29 View Post
    Here's my sad history. I'm in USA, a homeowner with pretty much a new installation. (R410A) It's "pretty much new" due to a tech from a now-fired company trying to fix hunting and inadequate cooling, on a second call-back, by adding more charge, and more charge, and more charge... And it all blew up after he left. (Probably the Evap first, but the Compressor quickly followed.)
    This isn't near enough information for a proper evaluation. But... given this limited information, at this point my guess would be evaporator airflow problems... most likely undersized ducts.

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    Re: We're adjusting, and I TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by Gary View Post
    This isn't near enough information for a proper evaluation. But... given this limited information, at this point my guess would be evaporator airflow problems... most likely undersized ducts.
    Your 'guess' is the first place I'd look, too. But airflow is excellent, absolute bulb temps are excellent, humidity control and overall cooling are already pretty good. After today's commissioning, I'm willing to guess that it will be VERY close to optimal and it's VERY close to optimal after about one full twist towards more more flow, and maybe some recovery of coolant to reduce excess SC.

    But thiswas as "close" as we were willing to go today; outdoor ambient temps were barely 80F today, the real "tuning" needs should be for standard conditions (As close as we want to "try" when ambient temps are so low-- barely 80F today.) Here's what we've got, and what we did:

    42,000 BTUH compressor, Trane XL14i.
    60,000 Evaporator, Advanced Distributor Products ("ADP")
    Note: This is an ARI certified combination at SEER 14.00, although my electric costs always seemed a bit too high, even when new.

    Upgrade: Danfoss "TR6" TEV, nominal size 36,000 BTUH.

    All 3 components are new. (Lineset and Condenser Coil are unchanged.) We removed the ADP-provided TEV, installed the Danfoss. Also installed a Schrader valve near the evaporator, in front of the TEV, to check pressure/subcooling directly at the TEV (that's where it REALLY matters). As a frivolous enhancement, and because I had a small tube of the stuff lying around after a computer upgrade, I put some high quality thermal-transfer compound around the "contact line" between the Danfoss bulb and the return line, before wrapping it all up with insulation. (Arctic Silver #5. I figure, better thermal contact == better accuracy.)

    We did have a concern which prevents "fine tuning" today: Outdoor temps barely reached 80F, and the lineset has almost 25 feet through my attic (over a 3-car garage). When the outdoor temp exceeds 100F, common in July, temps in that space can reach 120+. We might have to insulate the liquid line, even though that gives up advantageous heat loss from the naked copper in more moderate conditions. One thing's for sure: Today, the liquid line was able to give off plenty of heat to ambient, even in the attic.

    Vapor line goes through that same attic, opf course, with only 3/8" "pipe noodles" as insulation. That's grossly inadequate and will be upgraded. Now remember, my house is at 5000+ ft, so we used a high altitude R410A pressure versus temp chart.

    After installation and charge-up (done properly) we had our first surprise: Line set is almost 40 feet long, one way, at Trane-specified diameters, but upon start up, subcooling was almost 20F at the outdoor coil, and even higher in front of the TXV. But superheat was also excessive (28F, even with my cruddy "noodles" insulation), so we concluded that the first thing to do was adjust the TXV for more flow-- before recovering any "unneeded" refrigerant.

    The need for "more flow" didn't surprise us at all-- big Evaporator, slightly undersized model of the Danfoss TR6. But the fact that the big Evaporator AND lengthy line set hadn't called for additional charge, IMMEDIATELY, upon the first start up, was a surprise. We'd expected to see lower pressure on the liquid line, but pressures were high-- at the TEV, and back at the outdoor Service tap too.

    After 3/4 turn counterclockwise (more flow, less "excess" superheat), and 15 minutes of running time, superheat was stable at 16F (a bit to high, even for "lazy" commissioning, and far too much for optimum performance-- but going the right direction.) liquid pressure and subcooling fell by only a tiny bit. That's what we expected with R410A, but we chose to at least "ballpark" the superheat before recovering coolant from the factory charge. While he did a bit of coolant recovery (his department, I'm not licensed!) I loosened the TEV spring adjustment by another 1/4 turn.

    And that's where we have left it: Superheat is now 13F, subcooling at the outdoor service port is 12F. Greater SC at the TEV, but some of that "excessive" SC at the TEV is partly due to heat loss along the naked line in low attic temperatures. I'll have him come back for final settings on a much hotter afternoon in July, when the attic nearly as hot as it can get (and both lines are insulated against that heat). At that time, we'll adjust for much tighter settings: About 4F subcooling (in front of the TEV), and about 6F superheat (in front of the compressor). Total Pressures are just slightly off from Trane design specs already. Just a few PSI on both sides (increase on Vapor side, decrease on liquid side.)

    - - - my summary - - -
    Well, it took considerable time and money. (TXV was only $70, but I also had to buy a pound of low temp, high-silver solder-- and in USA, it's almost impossible to obtain the old lead-based stuff. (So I bought J.W. Harris Stay-Brite #8, a non-lead non-cadmium premium product, at nearly $45 shipped.) I handed my installer the almost-full spool, as a gift, at the end of the install. But for a fully-equiped pro, the TEV and maybe a couple of new Service Ports are the only hardware items-- hundred bucks or so, unless you go with cheapo Schrader valves (and depend on no-loss adapterd for connecting/disconnecting measuring equipment while pressurized.)

    Even with the all the finicky wet towel wrapping, he was done with the TEV in only 45 minutes. (I did provide a spare hand in the process, spraying water to keep the paper towels well soaked.) We did, however, make a major mistake with our install: ADP had mounted the non-adjustable "one size fits all" TEV inside the cabinet; and, without thinking enough, we put the new one exactly where the old one hads been.

    WRONG! Each of the 3 adjustments required removal of the case panels, a bit hard to get at, with several minutes of flex-duct taping to seal all BIG gaps surrounding the FOUR (4, WTF ???) drainage connector sockets. (Rectangular cutouts in the panel for pairs of round PVC drainage connectors, huge amounts of leakage before taping.) And of course, removal of the panels requires that the A/C be shut down to avoid blowing indoor air all over the place. We should have mounted the new TEV in a segment of horizontal liquid line OUTSIDE of the evaporator coil case. So the "tuning steps" took almost two hours; run continously, when adjustment made while running, it would have taken barely 45 minutes.

    ADP, in contrast, didn't even insulate the bulb of the "one-size-fits-all" TEV. And here's the instructions:

    1. Run system for at least 10 minutes to allow pressure to stabilize.
    2. Add or recover refrigerant until subcooling matches this table: Min=10F, Nominal=12F, Max=14F.
    3. Then, if equipped, adjust the valve until the superheat matches this table: Min 8F, Nominal 10F, Max 12F.
    I agree with #1, but for 15 minutes after each change. I totally agree with the idea behind #2, but I label the figures as bogus: ADP didn't provide any kind of service port in front of the TXV, so they seem to be assuming that you're measuring outside. And thus, they provide 6-10F of "extra" SC to make up for heat which MIGHT be gained in hot attics, and pressure which MIGHT be lost in filters/driers, and so on. I'm feeling that a lot of bad things can happen to that pressure, as well as the actual line temp, between the Condenser and the TEV. The subcooling figure which really matters is the one taken at the TEV: If you don't have about 3-4F of protection against bubbles at that point, you're either (a) undercharged; (b) losing a lot of pressure from something which needs to be FIXED or CLEANED UP; or (c) gaining heat along the path.

    My theory on this step is: you check the high side pressure and temp at the outdoor Service Point only to confirm that it isn't badly wrong or widely different than the pre-TEV measurements. Big looses of pressure imply restriction, (needing clean up or filter replacement), or perhaps a missed leak. (Shouldn't be there, though, because YOU CHECKED.) Any GAINS in temperature need to be prevented. Actual "tuning" of charge and SC should be based on measurement at the TEV, and more than 4F (excluding undependable temp losses in cool outdor conditions) is making the compressor work too hard, and wasting electricity.

    But it's their step 3 where they really fell on their faces. "If equipped, adjust the valve until the superheat matches the table." They don't offer an adjustable TXV, you have to buy one yourself. As I just did. Furthermore, their installation guide says tht it's important to match the size of your compressor, but they sell only two sizes: One for everything up to 3.5 tons, And the other for 3.5 all the way to 5.

    Adjustable spring tension alone can't make a TEV respond to varying conditions. You CAN crank the spring up or down for one set of conditions, but if the orrifice size is wrong, the adjustments won't work right-- you'll tend towards flooding in one direction, and tend towards starvation in the other. All the mfgrs make a much greater number of products than ADP offers: one size for 12,000 BTUH, another size for 18,000 BTUH, another size for 24,000 BTUH, and yet another size for 36,000 BTUH! ADP makes it easy to order, with just one product for R410a and the other for R22, but the one size can't really work well for all of these different compressor sizes.

    It's already working quite well, and So I'm already delighted with the

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Iceman makes the point of wire draw, I have no idea what that means. Of course if an HFC, HCFC or CFC plant were operating short of refrigerant for a long period of time this would wear the orifce seat and valve needle due to the increase in friction. Again it would be pointless adjusting the valve, although you might get away with a new orifice.

    Is this the same as 'wire draw'?
    Last edited by Refrigerologist; 11-03-2008 at 09:06 PM. Reason: Grammar

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    whether to adjust or not the txv is an option doing the job.in my experience,txv of the orifice type often need to adjust,while fixed capacity txv seldom need adjustment.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    I mostly install Danfoss TEV. I find them to have a good factory setting suitable for most normal conditions. It is however absolutely necessary to decrease the superheat when installing a system with a low TD evaporator.

    I once conected a new blast chiller to a sentraliced system operating at -8c. Coudn't get the temperature in the chiller below +3c. Found the TEV was adjusted to 10k static superheat. As the temperature in the chiller aproached 10k above evaporation temperature, the TEV closed completely. Adjusted the TEV to a few k static superheat. Afterwards I got the temperature down to -2c or -3c. No problem with liquid entering the compressor as the system has a suction gas/liquid line heat exchanger.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by SteinarN
    It is however absolutely necessary to decrease the superheat when installing a system with a low TD evaporator.
    That is a valid point and one not often considered. I forgot about this when posting my comments earlier (although I have mentioned this before in another thread somewhere). If the static superheat setting of the expansion avlve is less than the temperature difference of the evaporator you can have problems with loss of capacity or higher discharge temperatures.

    You cannot get more superheat than you have temperature difference. This is a practical limit to recognize in my opinion.
    If all else fails, ask for help.


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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Refrigerologist,

    Wire drawing is where the pin carrier and needle are eroded due to flash gas in the liquid feeding the TXV. This happens over a period of time on ammonia valves which requires them to be rebuilt occasionally.

    If you have seen a piece of wood that has termites or worms feeding on it, the pin and needle look something like this, only rougher.
    If all else fails, ask for help.


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    Re: TXV's To Adjust or Not to Adjust - That is ....

    One last comment while I'm on this subject for now. When I suggest the general rule of not adjusting expansion valves it is based on preventing other problems.

    All too often people start to adjust the TXV's (or replace them) as a general service practice when performing analysis of refrigeration systems.

    This happens in much the same way as adding refrigerant to the system when cooling is not sufficient.

    What I'm trying to suggest is that people need to increase their skill levels and understanding of how things work.

    The problem with adjustment stems is that people like to turn them when something is not correct.
    If all else fails, ask for help.


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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by US Iceman View Post
    Refrigerologist,

    Wire drawing is where the pin carrier and needle are eroded due to flash gas in the liquid feeding the TXV. This happens over a period of time on ammonia valves which requires them to be rebuilt occasionally.

    If you have seen a piece of wood that has termites or worms feeding on it, the pin and needle look something like this, only rougher.
    Thnaks Iceman, so it is the same as an HFC or CFC system, flash gas in the liquid line, or shortage of gas causes the problem. I have never heard it given that name before! I always called it needle and/or orifice seat wear!
    Last edited by Refrigerologist; 10-04-2008 at 08:00 PM.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    An expansion valve should be adjusted if it needs adjusting. The problem is that most service techs can't tell if it needs adjusting or not, so they end up causing problems instead of curing problems. When in doubt, leave it alone. TXV's almost never need adjustment.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    [quote=Refrigerologist;96601]Many engineers' in this industry say "you should never adjust a TXV superheat setting as they are factory set".

    This is correct and if you select the right size orifice no adjustment is required . Its all about knowledge and experience , however not everyone knows how to select the correct size orifice they then start messing with the t.e.v ?? why o why just leave them valves alone and get some training

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    [quote=philfridge;100895]
    Quote Originally Posted by Refrigerologist View Post
    Many engineers' in this industry say "you should never adjust a TXV superheat setting as they are factory set".

    This is correct and if you select the right size orifice no adjustment is required . Its all about knowledge and experience , however not everyone knows how to select the correct size orifice they then start messing with the t.e.v ?? why o why just leave them valves alone and get some training
    If you read some of my previous posts you will see that I completely disagree. Valve superheat should always be checked and adjusted as per individual system requirements. As I have said, if we are not to adjust the valve then the manufacturer would not bother to fit an adjustment screw I would suggest you look at a selection catalogue for, say Danfoss valves, it will show that an orifice will provide different capacities at differrent conditions and the valve cannot be factory set to cover all of the possible conditions that the valve will need to cover!
    Last edited by Refrigerologist; 10-04-2008 at 07:59 PM.

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    Thumbs down Re: TXV's To Adjust or Not to Adjust - That is ....

    [quote=Refrigerologist;101113]
    Quote Originally Posted by philfridge View Post

    If you read some of my previous posts you will see that I completely disagree. Valve superheat should always be checked and adjusted as per individual system requirements. As I have said, if we are not to adjust the valve then the manufacturer would not bother to fit an adjustment screw I would suggest you look at a selection catalogue for, say Danfoss valves, coit will show that an orifice will provide different capacities at differrent conditions and the valve cannot be factory set to cover all of the possible conditions that the valve will need to cover!
    Like i said you do not need to adjust the valve if you know what you are doing with orifice selection . As you mentioned Danfoss valves these are preset at 2 1/2 turns out and this does not need any adjustment in my experience

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    [QUOTE=philfridge;101154]
    Quote Originally Posted by Refrigerologist View Post
    Like i said you do not need to adjust the valve if you know what you are doing with orifice selection . As you mentioned Danfoss valves these are preset at 2 1/2 turns out and this does not need any adjustment in my experience

    I completely disagree, comparing a danfoss tuae valve which has 9 selectable orifice sizes to say a sporlan balanced port valve (SBF series) which has only 5 - leaves a lot of room for mismatching evap load to valve capacity with the sporlan valve. If you believe EVERY single valve will keep 6K superheat then maybe you need to set up some more evaps... distributor and coil design have a big influence on how a valve behaves as well - this is why every valve should be evaluated for its performance and adjusted if necessary to keep a stable superheat.

    I commission supermarket cases nearly every day (or night ) and have been doing so everyday for nearly 8 years straight now and I cannot tell you how many of the same cases with the same evaps, distributors and txv's I come across... if you think they all behave the same as far as superheat control you have another thing coming. I use an Einstein or RMCC in a suitcase and setup probes to log and graph their performance, there are differences in their factory setting to say the least, Alco valves are the worst as far as differing behaviours for the same given conditions, then sporlan and I'd have to say Danfoss are probably the best as far as consistency goes.

    I'd love to just start them up and skip the whole txv logging and adjusting but unfortunately the supermarkets over here have consulting engineers that will randomly check superheat in each store on handover - if its not between 4 to 6k you will be made to do them all again .
    Last edited by 750 Valve; 11-04-2008 at 01:09 PM.
    ...and she said "give it to me you big fridgie"

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    [quote=750 Valve;101205]
    Quote Originally Posted by philfridge View Post


    I completely disagree, comparing a danfoss tuae valve which has 9 selectable orifice sizes to say a sporlan balanced port valve (SBF series) which has only 5 - leaves a lot of room for mismatching evap load to valve capacity with the sporlan valve. If you believe EVERY single valve will keep 6K superheat then maybe you need to set up some more evaps... distributor and coil design have a big influence on how a valve behaves as well - this is why every valve should be evaluated for its performance and adjusted if necessary to keep a stable superheat.

    I commission supermarket cases nearly every day (or night ) and have been doing so everyday for nearly 8 years straight now and I cannot tell you how many of the same cases with the same evaps, distributors and txv's I come across... if you think they all behave the same as far as superheat control you have another thing coming. I use an Einstein or RMCC in a suitcase and setup probes to log and graph their performance, there are differences in their factory setting to say the least, Alco valves are the worst as far as differing behaviours for the same given conditions, then sporlan and I'd have to say Danfoss are probably the best as far as consistency goes.

    I'd love to just start them up and skip the whole txv logging and adjusting but unfortunately the supermarkets over here have consulting engineers that will randomly check superheat in each store on handover - if its not between 4 to 6k you will be made to do them all again .
    The quote at the head of your post is not one of mine. I believe valve superheat should be checked and adjsuted, if it is required, for every system on commissioning. In other words you will get no argument from me I will also add that I too find Danfoss valves to be the best and most consistent.
    Last edited by Refrigerologist; 11-04-2008 at 04:05 PM.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    What makes you kids think you're old?

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    Question Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by Gary View Post
    What makes you kids think you're old?
    Hi everybody Is there anything available in the market that can show the quantity of refrigerant charged in a system by just connecting it in to the system? plz. comment.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    philfridge, refrigerologist i apologise for the misquote - I don't know what happened... I just hit the quote button like I normally would, lots of the quotes in this thread appear to be messed up

    Anyway i completely agree with US Iceman in regards to total suction superheat and mass flow rates, one of our customers - a large supermarket chain in aus specifies a maximum suction superheat (as do the comp mfg's) but fits stub probes and really likes to see around 10K at the stubs entering the suction header, which normally lands the evap superheat around the 4 to 6K mark, and yes this total superheat is affected by line sizing and insulation quality, and I guess through experience 10K provides a decent mass flow rate (when compared to say 20 - 30K). It can make setting stores up a little tedious when they are so perdantic (spelling?) about stub temps, it requires a little tweaking to keep them satisfied with both evap and total superheats but I guess it keeps us commissioners on our toes a bit.
    Last edited by 750 Valve; 13-04-2008 at 09:02 AM.
    ...and she said "give it to me you big fridgie"

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by 750 Valve View Post
    philfridge, refrigerologist i apologise for the misquote - I don't know what happened... I just hit the quote button like I normally would, lots of the quotes in this thread appear to be messed up

    Anyway i completely agree with US Iceman in regards to total suction superheat and mass flow rates, one of our customers - a large supermarket chain in aus specifies a maximum suction superheat (as do the comp mfg's) but fits stub probes and really likes to see around 10K at the stubs entering the suction header, which normally lands the evap superheat around the 4 to 6K mark, and yes this total superheat is affected by line sizing and insulation quality, and I guess through experience 10K provides a decent mass flow rate (when compared to say 20 - 30K). It can make setting stores up a little tedious when they are so perdantic (spelling?) about stub temps, it requires a little tweaking to keep them satisfied with both evap and total superheats but I guess it keeps us commissioners on our toes a bit.
    No argument from me here! I just wish I hadn't started this thread, I knew it would be trouble
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    Re: TXV's To Adjust or Not to Adjust - That is ....

    If the fans are not runing and the valve closes, what difference does it make which orfice size is installed? Closed is closed. If the coil is flooding the valve should respond unless the piping arrangment and bulb location permit flow through the bottom of the suction pipe without cooling the bulb.
    There will be little or no superheat to open the valve.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by Refrigerologist
    I just wish I hadn't started this thread, I knew it would be trouble
    Call it a community service.

    It might seem like you opened Pandoras box, but I don't think so. These are the types of discussions that once in print help to support learning for others.

    The only down side in setting the TXV's to control the total superheat is that now the compressor bodies may sweat or have frost on them depnding on the application. Then someone thinks the compressor is flooding back and resets the TXV's so the compressors run HOT AGAIN!
    If all else fails, ask for help.


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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by NH3LVR
    If the fans are not runing and the valve closes, what difference does it make which orfice size is installed? Closed is closed. If the coil is flooding the valve should respond unless the piping arrangment and bulb location permit flow through the bottom of the suction pipe without cooling the bulb.
    There will be little or no superheat to open the valve.
    Or unless the power element lost it's charge. Then it could potenitally seep liquid since the valve is only responding to pressure changes alone (inlet and outlet).
    If all else fails, ask for help.


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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by US Iceman View Post
    Or unless the power element lost it's charge. Then it could potenitally seep liquid since the valve is only responding to pressure changes alone (inlet and outlet).
    I need to think about that awhile. The few cases I have seen the TX valve shut down when the head failed.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    i have enjoyed reading this discussion so far but would like to ask what should the procedure be when, in these times of energy saving, consulting engineers are requesting that operating condensing pressures be reduced from 14.5 bar to 11 bar. if the performance of the valve is in part based on the pressure drop across it, then surely a 3 to 3.5 bar decrease in pressure drop would naturally change the valve/orifice combination's capacity. this surely would therefore force a change of orifice or superheat setting. we do not however receive instruction on this with the comment "the change is not large enough to warrant replacement or adjustment". i have not yet made the time to measure any change, but the 25% change in pressure drop woluld surely have a significant effect on the system operation. does anybody have experience of this?

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Hav to say one of the best discussions in a long time. Spent 7 yrs at a counter now 14 years field with 7 owning my company. Same rule stands... don't mess with a valve unless you have a spare on hand. Totally agree that some techs like to think they know how to read and set properly. A couple of nightmare situations and a " good " tech learns not to touch what he can't understand. I am learning everyday MY LIMITS and look for the problem before I apply the solution. Again....great discussion!!! Thanks.
    '

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by bill1983
    ...consulting engineers are requesting that operating condensing pressures be reduced from 14.5 bar to 11 bar.
    This is easy to do in the winter time with air-cooled condensers since the condensing pressure set point can be set to lower pressures. You have to remember in this situation the liquid coming off of the condenser has a lot of subcooling or is much colder than normal (in summer).

    The colder liquid tends to increase the valve capacity, while the lower differential pressure causes the valve capacity to be reduced.

    Therefore, what you loose in one condition the other helps to increase. You have to look at the manufacturers ratings and correction factors to see where indeed this balances out in the this condition.

    On the other hand, trying to lower the condensing pressure in the summer is a limit of the condensing heat transfer surface available. If the condenser was sized to reject the full load heat at 14.5 bar, then that is where it will want to operate.
    If all else fails, ask for help.


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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by jeffrey5151 View Post
    Hav to say one of the best discussions in a long time. Spent 7 yrs at a counter now 14 years field with 7 owning my company. Same rule stands... don't mess with a valve unless you have a spare on hand. Totally agree that some techs like to think they know how to read and set properly. A couple of nightmare situations and a " good " tech learns not to touch what he can't understand. I am learning everyday MY LIMITS and look for the problem before I apply the solution. Again....great discussion!!! Thanks.
    '

    You are right - don't touch what you don't understand, but if you can't adjust a txv to maximise its operation and just change them whenever they don't do what you want, then... well.... um... I'm lost for words.
    How would you go getting a butcher's coldplate to flood fully and not smash valveplates? They don't always do what you want out of the box and no amount of changing parts will help you. Sometimes you need to use the old noggin (aka grey matter) and spend the time to watch the evap operation.

    Most danfoss valves require a PD of between 10 and 12 bar across the valve before capacity is dramatically reduced and as mentioned before the subcooled liquid temps decrease the percentage of flash gas and thereby allow capacity to be increased.
    ...and she said "give it to me you big fridgie"

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    I just want to add here, that most of the tools we have to measure superheat, are not calibrated, low accuracy and repeatability, and measurement's (pressure) are often not taken at evaporator. That fact of life also makes few more arguments in favor to not adjust TEV unless you are 100% sure that it is needed and that your measured data are of any good.

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by nike123
    I just want to add here, that most of the tools we have to measure superheat, are not calibrated, low accuracy and repeatability, and measurement's (pressure) are often not taken at evaporator. That fact of life also makes few more arguments in favor to not adjust TEV unless you are 100% sure that it is needed and that your measured data are of any good.
    Some very good points! I might add some comments about the pressure/temperature relationship of the refrigerants also.

    At low pressures the equivalent saturation temperature can significantly change due a small pressure loss (or bad data from gauge). While at higher pressures the effect of pressure loss ( or again bad data) present much less of an issue.

    If you will forgive the IP units... A difference of 1 psi in the gauge reading can amount to as much as 5 or 6 degrees temperature change at low temperature (depending on the refrigerant). At high temperatures, a pressure difference of 1 psi may only be equivalent to 1 degree or less.

    So yes, the accuracy of the gauges and data used is very important. On a low temperature display case that might be set for 6-8 degrees (evaporator superheat in Fahrenheit scale) an error of 3 or 4 degrees due to bad data could cause the compressors to run hot or flood.
    Last edited by US Iceman; 14-04-2008 at 03:36 PM. Reason: added details
    If all else fails, ask for help.


  45. #45
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    Exclamation Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by Refrigerologist View Post
    Many engineers' in this industry say "you should never adjust a TXV superheat setting as they are factory set".

    I would welcome comments on this statement.
    Personally, I will agree with this statement, many TXV is already pre-set from the factory.

    But certain case, only by "professional" in refrigeration, you may do some adjustment, which you can find in instruction letter come along with TXV packaging, mentioned to turn clock-wise or anticlockwise vice versa. But straightly recommend only for "professional", which they may spend whole day or even couple days for "tune" and "adjust" TXV into the right proper system they want it to be.

    Hope this is usefull.

    Regards,

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by sugino_m View Post
    But straightly recommend only for "professional", which they may spend whole day or even couple days for "tune" and "adjust" TXV into the right proper system they want it to be.

    Hope this is usefull.

    Regards,
    Yer sounds like my kinda job spending a day or two to adjust a t.e.v . Whats the pay like

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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Thanks guys. A very good debate. No winners or losers though
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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Are you throwing in the towel?

    This was a good discussion and now it's recorded for posterity for one and all.
    If all else fails, ask for help.


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    Wink Re: TXV's To Adjust or Not to Adjust - That is ....

    Quote Originally Posted by US Iceman View Post
    Are you throwing in the towel?

    This was a good discussion and now it's recorded for posterity for one and all.
    Yep! Towel well and truely thrown in. I couldn't take any more beatings from you guys
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    Re: TXV's To Adjust or Not to Adjust - That is ....

    Hello guys
    I am new here
    But I think superheat should be checked (and adjusted if needed)on commissioning because you can never be shore what they did in the factory

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