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FreezerGeezer
13-08-2001, 07:20 PM
I agree with NOT adjusting TEV's after comissioning.
I don't know if any of our commissioning engineers made adjustments back when I did install. But I was always taught that the TEV was factory set for the case (always providing you installed the correct orifice, of course), and that if the superheat was wrong, adjusting the bulb was unlikely to correct the actual fault.
Now I work on Chillers. These things are factory built. However, I have collegues who insist that if the superheat is wrong, the TEV must be adjusted. No doubt they may be right, but I personally like to know that there's nothing else causing the problem.
Am I wrong? Maybe. Any comments?

Dan
14-08-2001, 07:33 PM
The TEV should be the last thing to touch. Perhaps that is a better way of stating it. Perhaps a questioning mode is in order.

Why would anybody want to adjust a TEV?

Floodback or overfeeding?

Starving or underfeeding?

Aren't there many things to consider and look at before we remove the cap from the adjustment stem?

Unstrapped TEV bulb? Flash gas? So many things that can result from system dynamics such as heat reclaim and gas defrost shifting in and out, head pressure control settings. Low pressure control settings.

Every setting of every control has to be considered before adjusting the TEV. That includes questioning the size and powerhead of the TEV.

Or said another way, make sure you understand what is going on throughout the entire system before you adjust the TEV.

Dan

Gary
14-08-2001, 08:43 PM
I couldn't agree more. Even in comissioning, adjustment usually isn't needed. The factory setting will get you where you want to go.

The only legitimate reason is to fine tune the system, and the superheat shouldn't be checked until everything else is checked.

Even then, the measurement and/or adjustment won't be accurate until the refrigerated space is very near the cut-out temperature. Under heavy load, the TEV is wide open, acting just like a fixed orifice device.

Prof Sporlan
15-08-2001, 02:30 AM
TEV's often easily maintain superheat stability down to 30% of their design load, especially if suction and head pressures are stable. However, constantly banging 50% condenser capacity in and out doesn't provide for the most stable of conditions and can be an obstacle to the technician doing his best to set TEV superheat for optimum efficiency.

Amen! The Prof recalls a phone conversation he had with a technician who was having difficulty stabilizing TEV control. After spending some time reviewing some of the more typical causes of this problem, the technician noted that the TEV hunt seemed to follow the cycling of the condenser fan, which was cutting in and out every 30 seconds or so on the system's head pressure control. So much for setting the TEV at "design" conditions... :)

Derek
15-08-2001, 02:53 PM
Have we missed something here.

Perhaps the manufacturers may wish to comment on 'factory set' I seem to recall that most were set to a bench test condition not rated condition.

Not a lot of difference and the tighter your system match the better . I always check the superheat and do adjust that's the way I was taught.

There are some people out their that say automotive spark plugs are factory gapped. Fine for the factory but in some vehicles well wrong. One size does not suit all.

FreezerGeezer
15-08-2001, 07:50 PM
Originally posted by Fridgetech
FrezerGeezer... aren't we short an e ?



Fridgetech, you're absolutely right! :o :o

I was in a rush to join in, and didn't check my spelling. OOoops!

I'll have to see if I can change it. In the meantime, thanks for the comments, everyone. Been in this game for a few years now, but sadly after apprenticeships died out. It's D***N hard to get good at this at my age! :D

Dan
15-08-2001, 07:54 PM
Perhaps the manufacturers may wish to comment on 'factory set' I seem to recall that most

In my view, whether spark plugs or TEV's, their adjustment is just simply the last thing to look at. The last thing to touch. Having your timing correct is primary, for example with an automobile engine. Knowing temperatures and pressures and such is primary with a refrigeration system.

Spark plugs fire pretty much okay from the factory, and TEV's feed pretty much okay from the factory.

Dan

Prof Sporlan
15-08-2001, 10:35 PM
If you don't mind the Prof borrowing from a post he recently made on another bulletin board.... :)

The Prof has no problem with a service technician who knows what he is doing to fine tune the setting of a TEV.

The problem one normally encounters with misadjusted TEVs is: (1) the technician really doesn't understand how the TEV functions, or how to measure superheat; or (2) perhaps as common, the technician does understand how the TEV functions, and how to measure superheat, but he attempts to adjust the valve when the system is not operationg at design conditions. Often, the TEV is adjusted when the system is pulling a room, box, or fixture down to temperature, which may cause the valve to overfeed when the system does reach design conditions.

The factory setting is going to get you into the ballpark if you have a correctly sized TEV. If you can't wait around to see temperatures reach design levels, your better off not messing with the valve.

FreezerGeezer
15-08-2001, 11:36 PM
Prof, granted that superheat will only be accurate @ certain conditions. I'd be interested to hear how others measure superheat.
Where I work, we do it by saturated suction temp & actual pipe temp difference.
Incidentally, we work on 10 deg. C subcooling. (taken as the difference between the saturated liquid temp, & the actual liq. pipe temp.) Any comments? At college, we were told it's not possible to achieve better than 3 deg. subcooling without sacrificing liquid. I suspect a different definition of subcooling is to blame.
:confused:

Derek
17-08-2001, 08:25 AM
Originally posted by Dan


Spark plugs fire pretty much okay from the factory, and TEV's feed pretty much okay from the factory.

Dan

Not a performance vehicle owner then Dan?

I think you miss the point how do you know that the factory set is the optimum performance set for your application?

You don't either you trust to experience and manufacturers repeatability or you test and adjust.

Its just a choice thing related to what you are working on. All mine are specials not a supermarket in sight.....

Gary
17-08-2001, 12:32 PM
In my view, whether spark plugs or TEV's, their adjustment is just simply the last thing to look at. The last thing to touch. Having your timing correct is primary, for example with an automobile engine. Knowing temperatures and pressures and such is primary with a refrigeration system.

I like this analogy. There are factors which have a much greater effect on system operation than precise (as opposed to ballpark) TXV superheat setting, and most techs have no idea what precise superheat setting means anyway.

It's been a long time since I was an auto mechanic, but if I had a choice between precise adjustment of the timing with ballpark spark plug gap, or ballpark timing with precise gap, I would take the precise timing every time.

Gary
18-08-2001, 02:12 AM
When we say the superheat is high, what are we really saying?

Are we saying that the coil isn't being fed enough refrigerant for the load?

Or are we saying that the load is too much for the amount of refrigerant being fed?

Think about it. This is just two ways of saying the same thing, and the problem could be either load or feed.

When we say the superheat is low, what are we really saying?

Too much refrigerant for the load? Or not enough load for the refrigerant?

Again, the same thing, and the problem could be either load or feed.

Or both.

There is more to superheat than just turning that stem.

Dan
18-08-2001, 03:24 AM
Not a performance vehicle owner then Dan?
LOL Derek.

Yes. I think that most performance vehicle people such as in race cars have predeveloped shortcuts for sparkplug settings. But from experience. And an automobile can be be much more finely tuned than a field installed remote refrigeration system can.

The drivers I watch throw away the spark plugs, for example. They have a self-contained system that they understand.

But I hearken to the fact that I can drive a car off the lot and it performs perfectly for the duty it is designed for.

I stand by factory settings as the last things to change. I stand behind the theory that there is an order of seeking and changing adjustments.

But this argument is meaningless to somebody who orders something off the shelf with an idea to change its behavior. The buyer becomes the designer, for example.

5 designers, even if flawed, do not need 500 designers in charge of their product in the field.

I love your difficult questions, Derek. I hope I address them to some degree.

Prof Sporlan
18-08-2001, 02:20 PM
Where I work, we do it by saturated suction temp & actual pipe temp difference.
Presuming that saturated suction temperature is determined by measuring suction pressure and converting it to temperature with a P-T chart? That is the preferred method.

Note that attempting to set the TEV to control a low superheat, say below 4F, can be tricky. The problem, of course, is the accuracy of one's gauges and temperature probe. The Prof recalls a technician who was amazed that he could be the TEV to control an absolutely steady 1.7F superheat. The Prof, of course, suggested that he adjust the TEV in somewhat, and get his intruments better calibrated if he plans to continue having the TEV control low superheats :rolleyes:

Derek
19-08-2001, 10:32 AM
Change of tack.

How about the use of control algorithyms such as those proposed and employed by JTL Systems (Suceeds) to overcome all the load v control issues. Supermarkets I know are not my area but the EEV over TEV relationship looks appropriate to any multi pack system.

Views on control as an art form rather than design condition.


PS I will still fiddle with my TEV's but then a pair of 16 channel data loggers helps......

Dan
19-08-2001, 10:19 PM
PS I will still fiddle with my TEV's but then a pair of 16 channel data loggers helps......

I hope you are not wasting all those channels looking at superheats alone.:)

Dan

Derek
20-08-2001, 08:43 AM
No way..

Using minimum 4 temperatures (max 15), 2 pressures (max 15), refrigerant flow and power transducers they are linked into a real time pressure enthalpy display for over 40 refrigerants CFC. HCFC, HFC HC and R717 giving an on screen PH diagram so you can trim systems.

The software also gives COP in refrigeration or heat pump mode. All load calculations in one go. Went on to link this to a compressor calorimeter.

Took months to develop (Tech Director did the hard sums)then I came to work here. Such is the quest for cash.

farfield
09-06-2002, 11:44 PM
Dan
Having the past expierance of shippers and havinmg been in the auto motive parts end, Check the spark plugs before you put em in. If one guy drops the box and the plug ends up getting bent its worth the time. Then dont adjust the TEV TXV which ever. Unless you try everything else first.

I had to adjust a TXV on a walk-in freezer last month. We ahd replaced the condensing unit last fall, and the TXV at the same time. We used a TXV approved for R404A and it worked fine til this spring when it had too great a setting of super heat. An Adjustment of 2.5 to 3 turns out and it was in range then. But the TXV worked fine all winter. And after looking it over for 3 times and then calling 2 others has to what procedure to persue it was indeed the SH setting.

SO IT IS good for some things to be adjustable. But not return springs on contactors. Never mind, another far out flop.

Dan
11-06-2002, 01:29 AM
LOL. I couldn't agree more that adjustable controls and valves are wonderful things. Or that the car that doesn't drive off the lot smoothly needs immediate attention.


We used a TXV approved for R404A and it worked fine til
this spring when it had too great a setting of super heat. An
Adjustment of 2.5 to 3 turns out and it was in range then.

Why would you change the superheat setting on a valve after the superheat setting was correct for so long? Usually, I expect to see a valve feeding correctly in winter, tend to overfeed when weather warms up. Overcharge is normally the culprit.

What do you think was going on there that you had to adjust the stem? Maybe just no load on the box and a starved coil with an underworked compressor could keep up? I can't think of another scenario.

Anyone else have any thoughts?

herefishy
11-06-2002, 06:27 PM
Likely the thermostatic element is beginning to lose it's charge. But, better yet, an ice-up was experienced reulsting in decrease of refrigerant flow/velocity, and lubricant filled the EQ port under the element diaphram (which likely is situated in a manner to trap the lubricant), and the TEV was adjusted in this condition, right after the coil was de-iced and the system was started back up.

But look. This idea that the TEV is "Factory set", is a bunch of Bunk! Yes the factory sets the valves at at a 9degF superheat setting simulating R-22 at a (selected) evaporating temperature, USING DRY AIR, WITH THE ELEMENT BULB IN AN ICE BATH!!!!!!!! The factory process of setting the valve "spring tension" should be considered merely a practice of establishing that the valve works, and to get you "into the ballpark" with a reasonable setting before evaluating the SH after the installation.

When you get "OEM" non-adjustable valves, the process of establishing what the "spring tension" should be is a process of the manufacturer installing a valve into their equipment, operating the equipment and setting the valve to their desire. The valve is then removed from the system, sent back to (Sporlan) who is told, "this is what we want". Then Sporlan hooks up the (OEM) adjusted valve to their "ice-bath-dry-air-superheat-simulator", and notes the reading of the outlet pressure of the valve. Then, all valves ordered by that manufacurer are adjusted to that "spring tension" as determined by the outlet pressure reading of the dry air, with the element bulb in the ice bath.

If such a "non-adjustable" TEV were employed in some other application, the TEV element bulb relocated, or anything else changes, the S.H. situation would change.

Anyone who buys an aftermarket TEV off the wholesaler shelf, puts it in and walks away thinking the factory setting is good to go, is ...... well,...... not well informed.

Just think...... you hear everybody (in this forumn) indicate that as SST decreases, superheat decreases. So how do you know that the conditions of any system that a valve is being employed in has been factory set at THAT SST, pressure drop, liquid temperature, etc... that the valve will be operating in?

;)

stella
10-05-2006, 11:00 PM
new engineer can someone tell me proper way to measure superheat and adjust valve understand it has to be done when space is at optimun condition cheers

Chopper
13-05-2006, 02:40 PM
Hi,
First thing first, every single refrigeration system is unique and different! TEV's are mass produced!
That alone tells you why your superheat needs to be checked and adjusted accordingly. Any decent comissioning engineer will know exactly when the operating conditions are stable enough to gauge the superheat and when to adjust.
In todays world where keeping energy consumption to a minimum, getting the most out of your evaporator is paramount. If you can control a relatively small superheat(6'C) and raise the evaporating pressure as a result, energy savings are achieved and compressor running hours can be reduced.

Regards

Chopper

Dr._Fleck
30-01-2007, 06:22 PM
I have installed 100s of coldrooms in my time, all with Danfoss sweat in TEVs and can honestly say i have not had to adjust a single one.

As regards to energy saving it would be so negligable it's not worth faffing about with.

From my service days i remember if i ever thought a valve needed adjusting it was always faulty... Adjust it if you want to... But (arnie voice)YOU'LL BE BACK

The MG Pony
30-01-2007, 08:37 PM
And you give me the so called bad valve I'll give it a nice methonol bath and quick cleaning and have a free perfectly working valve :D After re-adjusting the SH to my system of course :)

wkd
02-02-2007, 09:13 PM
OK so technically evaporator pressure should be measured,preferably as close to the evap as possible especially if long pipe runs are in place,then suction line temperature.Use your comparator to establish stauration temperature then subtract SAT temp from actual Temp this gives evaporator superheat.I mention pipe runs because a long suction line will induce pressure drop giving a lower pressure entering the compressor and depending on the insulation you will pick up heat along the line.The consequence of this is increase in temperature entering the compressor.TEV are usually factory set for a predetermined superheat.Chillers for instance that are tested in the factory will no doubt have the superheat checked and adjusted accordingly but and the big but is at what condensing temperature were they set at in the factory.Usual design on an aircooled chiller is 35 C ambient for 7 CLWT however if the fan control is set at a default and the ambient temperature is say 15 C in the factory the superheat will change as the ambient temp rises and increases the pressure diff over the TEV.So putting this to commissioning stakes if you set a unit to work and the ambient is either high or low and go back in the mid temp ambient chances are the superheat will be different.It is also important to check superheat at low load/low ambient conditions as well.
I could go on about this for ages but there you go just a feeler.

DeB
05-02-2007, 05:38 AM
I agree with herefishy and chopper. Each system, unless a standard production line model, is an individual system and should be adjusted individually to suit its overall balanced capacity and design conditions.I do not believe in "one size fits all".

Refrigerologist
11-03-2008, 12:40 AM
Herefishy and Chopper, I like where you are coming from! Spot on!

Another problem with the "never adjsut an expansion valve superheat setting" is when the system is blatantly underperforming and there is excessive suction superheat and the inevitable burnt out windings. Having worked with some partially trained shaved gorillas I have had the unfortunate experience of having to follow up on their lack of commissioning ability. One guy had the suction gauge fitted and the thermometer probe installed on the evaporator inlet. I couldn't argue with him until the customer went to make a cup of Rosy! According to him it was fine to have a half starved, half frozen coil, and a 30lbs/in2 suction pressure. R22 swimming pool dehumidifier, pool air temp 31 degrees C. That was a brand new teddington (factory set) valve with the correct orifice installed. All sitauations should be evaluated. What I would expect is that a correctly commissioned system would be allowed to reach close to design temperature and then the superheat checked! This I do, as I run my own small business and I am teaching my son. It seems to save me money in the long run. A little extra time commisssioning correctly. Very, very few call backs!

n2ri
05-12-2009, 08:41 AM
I see mostly a large percentage of very confused and misinformed techs in this thread. as I find on many of these web forums (why I do not and recommend my HVAC students not mess with most of these). not a good source of facts. :confused:

does anyone here even know what the abbreviations below stand for?

TEV =

TXV =

EEV =

AEV =

and what the other 10 plus types of metering devices are and how they work? (e.g. not in series with another metering device). why do you think AEVs are no longer adjustable as they once where?:rolleyes:

I can tell you from my own 40+ years experience in the field. anyone that services an Refrigeration system in the field and starts adjusting (re-engineering) the metering device (which has been working properly in the past year or more). is an idiot wasting his/her time and money as well as your boss's and customers, and will demean any reputation of having been a competent service tech/company to depend on for future business (while at the same time making the entire HVACR industry look bad).:mad:

also whom every was ranting on about their SUPER DUPER SCIENTIFIC COMPUTERIZED LAZER GUILDED LABORATORY TESTER, needs a reality check. this ain't lab equipment in a controled environment you are working on here. this is in the feild, run hard and maybe put away wet (if at all) machines.

so lets check the BS at the computer desk and stop spreading ignorance all over the World Wide Web:o

Thank you, Mitch:(

NH3LVR
05-12-2009, 02:07 PM
This is your second post on this forum.
Nice polite way to introduce yourself.

Segei
05-12-2009, 06:03 PM
I see mostly a large percentage of very confused and misinformed techs in this thread. as I find on many of these web forums (why I do not and recommend my HVAC students not mess with most of these). not a good source of facts. :confused:

does anyone here even know what the abbreviations below stand for?

TEV =

TXV =

EEV =

AEV =

and what the other 10 plus types of metering devices are and how they work? (e.g. not in series with another metering device). why do you think AEVs are no longer adjustable as they once where?:rolleyes:

I can tell you from my own 40+ years experience in the field. anyone that services an Refrigeration system in the field and starts adjusting (re-engineering) the metering device (which has been working properly in the past year or more). is an idiot wasting his/her time and money as well as your boss's and customers, and will demean any reputation of having been a competent service tech/company to depend on for future business (while at the same time making the entire HVACR industry look bad).:mad:

also whom every was ranting on about their SUPER DUPER SCIENTIFIC COMPUTERIZED LAZER GUILDED LABORATORY TESTER, needs a reality check. this ain't lab equipment in a controled environment you are working on here. this is in the feild, run hard and maybe put away wet (if at all) machines.

so lets check the BS at the computer desk and stop spreading ignorance all over the World Wide Web:o

Thank you, Mitch:(
I just compared the numbers. You are 51 years old. You have 40+ years of field experience. Did you go to the field from kindergarten?:eek:

US Iceman
05-12-2009, 11:53 PM
I just compared the numbers. You are 51 years old. You have 40+ years of field experience. Did you go to the field from kindergarten?:eek:

I did, so I suppose someone else could have also.

Back to the comments of n2ri. I agree with what was posted, however, I might suggest a slightly less condescending tone. While there is a lot of bad information on the internet and with it the ability to keep an identity hidden, it would be much appreciated if you didn't try to flame a lot of people on your first couple of visits.

monkey spanners
06-12-2009, 12:06 AM
I think i was eight or nine when i first started doing maintenance work with my dad on weekends and school holidays, had my own set of gauges :D

taz24
06-12-2009, 12:43 AM
I see mostly a large percentage of very confused and misinformed techs in this thread. as I find on many of these web forums (why I do not and recommend my HVAC students not mess with most of these). not a good source of facts. :confused:



If you don't let your students come on sites like this, why do you?





does anyone here even know what the abbreviations below stand for?

TEV =

TXV =

EEV =

AEV =

and what the other 10 plus types of metering devices are and how they work? (e.g. not in series with another metering device). why do you think AEVs are



I'm not sure if this is a question or a statement???






no longer adjustable as they once where?:rolleyes:

I can tell you from my own 40+ years experience in the field. anyone that services an Refrigeration system in the field and starts adjusting (re-engineering) the metering device (which has been working properly in the past year or more). is an idiot wasting his/her time and money as well as your boss's and customers, and will demean any reputation of having been a competent service tech/company to depend on for future business (while at the same time making the entire HVACR industry look bad).:mad:

also whom every was ranting on about their SUPER DUPER SCIENTIFIC COMPUTERIZED LAZER GUILDED LABORATORY TESTER, needs a reality check. this ain't lab equipment in a controled environment you are working on here. this is in the feild, run hard and maybe put away wet (if at all) machines.

so lets check the BS at the computer desk and stop spreading ignorance all over the World Wide Web:o

Thank you, Mitch:(

Wow you pack a lot into one post.

Why not slow down take a deep breath and start again a lot slower

\cheers taz.

.

NH3LVR
06-12-2009, 03:01 AM
This discussion could go on for a long time.
I will agree that TX Valves should not be adjusted more than once. If they start to misbehave an adjustment is not likely to solve the problem.
I am mostly a NH3 person and we usually avoid TX valves if possible. We often find that the valve seats are eroded and all the adjustment you do will not correct that.
I suspect that the ***** valves are set closer than the NH3 ones are when you get them.
I have had many experiences with under or over feeding valves that needed adjustment on startup. I just had five Krack Evaps replaced where I work and we had a orifice sizing problem from the factory. It was the classic oversize problem where the coil went from starving to overfeeding with no in between.
I witnessed the final superheat readings before I would accept the job as complete.
In my service days we always checked the superheat when we started a new coil or changed a valve. If you check it and it is a few degrees high why not correct it?
However there are other causes that need to be investigated first. In the job I just mentioned we had evap condenser cycling because of low load and cold temperatures. We had to cover the air intakes on the condenser and cycle the compressors by hand to avoid pressure variations and flashing. If you are not able to do this you cannot possibly make a satisfactory adjustment.
Thanks to the old timers I learned from.
But then I am one of them now.

US Iceman
06-12-2009, 03:31 AM
Thanks to the old timers I learned from.
But then I am one of them now.

Amen. Once upon a time I couldn't get a job working on ammonia systems because I was too young. Thankfully I've lived long enough to become one of the old farts.:D

digerious
11-01-2010, 11:17 PM
a tev with the correct orifice, i was taught, should only need adjusting no more than one turn either way when setting up.inside a danfoss tev box there is a selection guide for each orifice.each orifice is suited for a certain range of duty at a given evap temp and refrigerant. the adjustment is there to allow for the difference in duty each orifice is allowed.slight adjustment is expected.its when adjustments of 2 or more turns are needed that alarm bells should ring.rightly or wrongly i was taught in college that when a system has run, not slightly short, or nearly empty of gas, but roughly at half charge, the mixture has the capacity to cut away at the orifice seat and allow more refrigerant through than is required, causing flooding to comp.this aswell as partial loss of bellows charge, along with all the more obvious underlying faults are the only reasons a tev may appear to require massive adjustment

NH3LVR
12-01-2010, 03:01 AM
i was taught in college that when a system has run, not slightly short, or nearly empty of gas, but roughly at half charge, the mixture has the capacity to cut away at the orifice seat and allow more refrigerant through than is required, causing flooding to comp.
What they taught you at college is indeed correct. I had this happen in a system that had been undercharged and ran for a long time. The system was a blast freezer running R502. At the end of the cycle when there was little load we started to get flood back. That was an easy one to figure. The process is called wiredrawing. It seems to be more pronounced on ammonia systems. Steam does this as well. Anytime you have a mixture of liquid and gas this can occur.

Magoo
12-01-2010, 03:28 AM
Have not had the last week to read all the posts on the topic.
"TEV adjustment ". Can only assume that no one understands TEV operation. You all accept that, that turkey in the office with a computer, that never went to site WAS CORRECT, with the TEV selection. And the commissioning tech that set system up was on a budget from nowhere [make it cold and leave, is common ].
Give me strength to carry on.
I have posted multi- posts on TEV selection and commissioning.
Believe me, working world wide TEV superheats are the diggest mistory that you lot cannot understand. It is not rocket science.
grumpy magoo

NH3LVR
12-01-2010, 04:48 AM
Have not had the last week to read all the posts on the topic.
"TEV adjustment ". Can only assume that no one understands TEV operation. t is not rocket science.
grumpy magoo]
Mr Magoo
That is rude!
I understand TXVs very well and do not consider myself an "Expert on the subject" Strange that I flew all over the Northwest USA and Alaska to sort these problems out and "I do not understand them".
Perhaps you should be nicer>;)

mad fridgie
12-01-2010, 05:23 AM
I find TEV to be very reliable the older one used to weep a bit down the equalising line and seem to be slightly more prone to being "drawn" (scratching of the seat).
However when it comes to adjustment, you must understand what the bulb, bellows and spring are doing. When you adjust the setting you are adjusting spring pressure, not superheat. At certain SST this spring pressure will equal a certain superheat at the bulb, at differing SST a different superheatsetting occurs. (refrigerant pt is not linear) So depending at what point you are in your system process, will determine what the valve superheat setting will be. This is more of a problem where your load fluctate and you have floating SST.
Example spring setting 0.5Bar
R404a -45C SST superheat would be 8C
R404a +5C SST superheat would be
2C
Would you adjust the valve for each one?

desA
12-01-2010, 07:24 AM
^ Nope, go for a cross-charge bulb... :D

mad fridgie
12-01-2010, 08:20 AM
^ Nope, go for a cross-charge bulb... :D
What is across charge bulb? can please explain how this effects the spring setting:D

simon@parker
08-04-2010, 04:53 PM
er dont no who trained ya an i dont mean to be rude sorry if i am when i woz 19 all the apprentices thought ooo tevs are all factory set went on danfoss course when they brought out the new tevs with indistructable cappillarys glen more ran it an boy did i look stupid when i said that .All tevs need to be set up no mater what make or who fitted them an if ya dont agree at least check it save ya alot of hassle if ya got a cabinett room or even water chiller that just aint workin rite an it an easy fix oh an yeah its been last thing i checked a few times on new and old systems an it was the problem

AlwaysLearning
30-05-2010, 08:58 PM
After I run through some checks, coils, fans etc, I will look at my TEV. I don't believe that the factory intends for thier setting to be permanent, they don't know what the application will be. I agree that they get it close but they put the adjustment on there to fine tune to your application. Just my opinion.

nike123
30-05-2010, 10:01 PM
After I run through some checks, coils, fans etc, I will look at my TEV. I don't believe that the factory intends for thier setting to be permanent, they don't know what the application will be. I agree that they get it close but they put the adjustment on there to fine tune to your application. Just my opinion.

And that should be done at commissioning! After that, it does not have any sense further fidlling with TXV adjustment.

dirk
30-05-2010, 10:19 PM
In 18 years supermarket work i have never had to set a valve superheat unless someone had previously scewed up the setting.
In case design selecting the coil is not only selected to match the case load but also expansion valve ratings.

chilliwilly
22-06-2010, 11:58 PM
I know this is an old thread but with me being new to the forum I would like to add my tuppence ha'penny to it.

If your using a drop in replacement refrigerant, you sometimes need to make fine adjustments to the XV. Due to the not quite matched compatability of the dropin to the designed system parameters.