expansion valve

[Ray Ang SM]

hello all engineer,im technician,new in this trade hope your guide me along.

may i know when ajust expansion valve how am i going to know ajusting the right amount.:eek:

[philfridge]

may i know when ajust expansion valve how am i going to know ajusting the right amount.:eek:




Do not tamper with the t.e.v as it is factory set and should not be adjusted , especially by the untrained. :off topic: .You can however select different size orifices to increase / reduce capacity.

[nike123]

hello all engineer,im technician,new in this trade hope your guide me along.

may i know when ajust expansion valve how am i going to know ajusting the right amount.:eek:

Check this thread!

http://www.refrigeration-engineer.com/forums/showthread.php?t=11903&highlight=adjust

[US Iceman]

Since you only said expansion valves I am assuming you are talking about thermostatic expansion valves (TXV). A new TXV should not be adjusted especially since you are asking this question.

All too often people think they need to adjust a TXV to cure some issue they believe will be corrected by this action. My suggestion is to resist the temptation.

Unless someone has completely made a mess of things with prior adjustments, it is my experience that suggests a TXV should not be adjusted.

[icecube51]

Go there,

http://www.danfoss.com/Products/Categories/Categories.htm?segment=RA&category=http%3a%2f%2fwww.ra.danfoss.com%2fra%2fProducts%2fProductCatalogue.asp%3fNavigation%3dHideO nAllPages%26Footer%3dHideonallpages%26Division%3dRC%26HL%3d1%26TopViewItem%3d84%26AppID%3d%7bc2a95da c-5e01-47df-92cd-5972d837cf1a%7d%26dyn_lang%3d

sorry, can not find easier way,

Ice

[icecube51]

oops forgot, if you are there, click on literature, and on the + for languish, you see:o

Ice

[archibaldtuttle]

So, here is the corrected link to Sporlan bulletin 10-9 which is their equivalent of the Danfoss circular cited above and is referenced with an old URL in the "TEV to adjust or not to " thread

I hate it when they keep moving this stuff around.
(sorry, if you notice there is no link there, i'm not allowed to post links yet. perhaps a wise management technique but frustrating, guess I just have to keep posting to get by the threshold -- but suffice it to say that eh link in the "adjust or not" thread is no good no more. you have to go to parker.com. pick the sporlan division under the products link, then on the right there is a literature link and one of the choices under that is bulletins and the 10-9 is about the 6th down or so but they aren't in reliable numerical chronology so you just have to look for it.)

So I have a question which is both related to correct adjustment but to the correct sizing question as hashed over more thoroughly in the adjust or not thread. The Trane 15 ton unit I've been working on as various threads attest for the last 4 or 5 days has two 7.5 ton circuits but was fitted OEM with Sporlan XVE 5 TEVs.

The 5 is the tonnage designation. Now I know it really means a range of tonnage (and operating conditions). And I'm not clear that there is a standard of designation such that all manufacturers when they put a number rather than a range on the valve are putting the cente of the range or the upper or lower confidence limit.

From a design standpoint I'm interested as we are replacing the burnedout circuit and replacing the TEV while we got the thing apart because at some point it was replaced with a valve (maybe an ALCO) that doesn't appear to have a head that can be removed and replaced. I already picked up an 8 ton R-22 replacement (ain't got it with me so I can't remember the temp range) bit I think the normal range for a chiller is different, i.e. warmer, than for straight air con.

So what I'm getting at is, if you have the choice of valve would you perfer the smallest valve that can handle the load presuming that you would get more subtle flow adjustment across its range? That is my intuition now that I already own one that's too big both from having stopped to reason it out and from having finally crawled underneath the chiller and found the sporlan designation on the one OEM valve that remains.

I'm flipping through the sporlan bulletin I just printed out and they use the desired pressure drop and the liquid temp entered the valve to guide you through capacity tables, only they don't say where the capacity tables are. I'm assuming these are maybe in the product line literature, and all of this maybe gets you a little closer to a 'correct' answer but I'm wondering about the scientific and emperical rules developed by cohabitants here at R-E.

Thanks for any response, and by all means feel free to be as ebullient, logorrheic, or caustic as you were in the adjust or not thread to get any of this through my thick skull.

Thanks.

brian

[get the gauges]

don't touch

[US Iceman]

So what I'm getting at is, if you have the choice of valve would you prefer the smallest valve that can handle the load presuming that you would get more subtle flow adjustment across its range?


I have always been of the opinion that the valve capacity can be slightly smaller than the actual load required. My reasoning for this is the slightly smaller TXV's control superheat better than a valve that is slightly over-sized.

If you look in the bulletins the pressure range range cause a change in the valve capacity. The capacity stamped on the valve tag is a nominal capacity, or as you say a range.

What you have to consider when selecting a TXV is the expected range of operation the valve will see during any perceived condition (summer or winter are the two big concerns, although part-load is another).

If the pressure differential has the ability to vary greatly you need to determine if this causes a problem with the valve capacity (as in too high or too low).

If the actual valve capacity can get too high during one of these conditions, then the slightly smaller valve might be more acceptable.

[GXMPLX]

I have always been of the opinion that the valve capacity can be slightly smaller than the actual load required. My reasoning for this is the slightly smaller TXV's control superheat better than a valve that is slightly over-sized.



Nothing personal Iceman!
NO I wouldn't do this. Depending on manufacturer but usually TXVs don't open more than 1,2 their nominal capacity (some 1,1). If this is the case (like it usually is in a blast freezer) you
1) Limit the highest suction pressure to a lower value affecting cooling time.
2) Possible adversely affect the STABILITY of the TXVs controll because it cannot feed more than its fully open state and will stay there for a while longer than necessary to react fast to sudden changes in load.

No problem if you do this in a maintenance room with stable temperatures and/or stable pressures.

It's better to follow manufacturer's recomendations because they know their product, flaws your worst nightmares wouldn't conceive, and they have done thorough testing (hopefully).

[US Iceman]

Nothing personal Iceman!


Absolutely no problem at all. We're just discussing things.;) Besides, you are really making me think!




Possible adversely affect the STABILITY of the TXVs control because it cannot feed more than its fully open state and will stay there for a while longer than necessary to react fast to sudden changes in load.


My impression is the stability would improve because the valve would be operating close to it's maximum. When this situation occurs it is my impression the valve superheat would actually increase slightly, so you would end up with slightly better control without flooding back. At least that is how I understood the valve capacity curves published by Sporlan.



Limit the highest suction pressure to a lower value affecting cooling time.


I can't really see that happening. I'm not suggesting the use of a greatly undersized TXV.

[GXMPLX]

My impression is the stability would improve because the valve would be operating close to it's maximum. When this situation occurs it is my impression the valve superheat would actually increase slightly, so you would end up with slightly better control without flooding back. At least that is how I understood the valve capacity curves published by Sporlan.

I'll make you remember again the TXV reacts like a second order system and suffers overshoot. If you don't let a second order system do this it will stick to it's maximum output for longer time that the overshot lasts, thus increasing the time constant of the system (time needed to go back to stable condition within 2%)

I will have to get literature on this it'll take me a while ... yes! Few of my deeply POE fried neurons still work! go here: www dot crtech dot com/txvResponse dot html
(sorry you know us newbies cannot hyperlink).

[nike123]

I will have to get literature on this it'll take me a while ... yes! Few of my deeply POE fried neurons still work! go here: www dot crtech dot com/txvResponse dot html
(sorry you know us newbies cannot hyperlink).

Of course you can! You have more than 15 posts.

[archibaldtuttle]

don't touch

OK, so I'm not convinced it doesn't need a tweak but did get a bump on my results at HVAC-talk that my readings


170 psi head
48 psi suction

27.2 degrees evaporator outlet

looks like low load.

that is for certain as I think about it, since the unit was down many folks had the fans in their fan coils turned off. And when I first started and the building water was ambient temp I was in the high 50's or low 60's pressure on the suction side and will above freezeback on return temperatures. My delta T across the evaporator was 10 deg. I admit, after initial startup, I was monitoring outlet temp water temps as well as suction temp and system pressures, but I didn't think to keep checking the inlet temp., so while I know I had good circulation I wouldn't be the least surprised if my delta dropped down so maybe that is partly or wholly responsible for the frost back.

I'm a little surprised though that the outlet temperature didn't just fall more quickly and trip the staging control with a satisfied signal.

Which gets me back to my quest for a more sophisticated staging controller that would monitor rate of temperature change, maybe delta- T , outdoor temperature and use proportional algorithm to manage different loads in different conditions.


My impression is the stability would improve because the valve would be operating close to it's maximum. When this situation occurs it is my impression the valve superheat would actually increase slightly, so you would end up with slightly better control without flooding back.

I tend to buy into iceman's theory here, i.e. if the superheat rises a little, it will slow slightly slow the chilling of your load so you will approach your low limit temp more slowly. but then presumably as you approach it and the load lessens then the valve will start to close a little. I'm less experienced in close monitoring of overrun at this point or the relative precision of the different valves available although the "adjust or not" thread had several votes for Danfoss.

Finally, while I've decided on sticking with the OEM sporlan valve on this circuit because I think they probably got it right an the thing has worked fine with 5 ton valves on a 7.5 ton circuit for years, and this means that a single replacement head on the shelf will repair either circuit. My next question in this grand reno is whether a flare style liquid dryer is contraindicated.

I already bought a replaceable style filter canister as for suction cleaner drier since this is a burnout situation and there just isn't anything in flare in the 1 adn 1/8 range anyway, but the liquid tube is 1/2" OD and the location is workable for me to do a quality flare in these lines and then if I do get any indiciations that a filter change is necessary early in the life cycle to protect the new compressor, I can swap out the liquid filter without yet another brazing adventure since I'm going to have the whole thing open and flowing nitro at this point. Is replaceing the filter in the new suction can I'm installing sufficient anyway generally such that you wouldn't worry about a short term liquid filter replacement. Are even well hung filters with smaller flare connections too much of a potentional for leakage so I should stick to brazing anyway. am I overthinking this? :)

thanks,

brian

[icecube51]

for all the don't touch the valve guys,:rolleyes:

i wonder if the get could out by a cabinet owner, where there was " a technician" ho tempered whit the valves and completely deregulated them,

are the gone shout " don't touch to ?:(

well, i hope they now wat the are doing.

Ice

[BESC5240]

i wonder if the get could out by a cabinet owner, where there was " a technician" ho tempered whit the valves and completely deregulated them,


Icecube, this is exactly what US Iceman says :


Unless someone has completely made a mess of things with prior adjustments[/U], it is my experience that suggests a TXV should not be adjusted.

And I fully agree.

One should also concider that an identical TXV reacts differently on different evaporators. The ability to control a stable superheat (at low load) depends on the construction of the evaporator (distribution, volume, heat exchange) ...

[Andy]

Hello:)

In my experience very few TXV's are set anthing like they should be.

Only adjust a valve if you know what your are at.

I had two problem jobs to look at recently.
One a close control with low performance, which had been commissioned twice by the manufacturers representative. 13k superheat, dialed the valves in, and increased the air velocity off the floor grills.
Performance checked before and after, with airflows and air on/off conditions. By adjusting the valves we gained more than 30% capacity increase.

Roof top units, water carryover. Checked and found little or no supperheat and that was from the manufacturer. Adjusted the super heat, changed the air filters, set the air recirc/fresh air dampers and the problem was resolved.

When I was commissioning supermarkets, I would run all up and then go to the front end, the cases with the poor air offs were the ones that needed the valves opened out, usually one in three cases. If you had frost on the ht suction lines you had a valve which had come factory set, too far open, so you adjusted it.

There is no such thing as factory set, how the valve performs on site depends on the sizing and application of the valve, the ones slightly under sized needed opened up, the ones over sized needed closed in.

You could always use EEV's with transducers and they will set themselves.


Kind Regards Andy D

[Sridhar1312]

Thermostatic expansion valves are factory set and should not be tampered with.And there is no need to adjust as long as selection is correct.Normally TXV should be undersized and never oversized as it may aid in flooding of compressor leading to failure.

[Andy]

Thermostatic expansion valves are factory set and should not be tampered with.And there is no need to adjust as long as selection is correct.Normally TXV should be undersized and never oversized as it may aid in flooding of compressor leading to failure.

Hello Sridhar1312:)

Some valves may come factory set, (if they come on a packaged unit they should be).
But valves that come loose in a packet come with instruction on how to set them.

The basics of refrigeration as far as an service or commissioning technican is concerned is.

1/Superheat
2/Subcool

These must be measured to determine the system performance. When measuring the super heat and finding it high, and finding the condenser subcooling higher I would adjust the expansion valve open a little to see if this improves performance.

If I find the subcooling low out of the condenser and the superheat at the evaporator outlet low I would close the expansion valve in.


What I would ask of those who say the valves are factory set is what would they do, leave the system under performing until the compressor fails:(

The knob on the side of the valve is there for a reason;)

Alway check the superheat and the subcooling and, learn how to use them and you can adjust any expansion valve you come to without causing harm.

Hopes this helps.:D



Kind Regards Andy D

[US Iceman]

I can see the topic of TXV's is going to go on like the subjects of subcooling and superheat.:eek:

Any of my comments are based on what I have experienced with TXV's I have installed, or, that others have installed, replaced, or adjusted trying to solve any perceived fault that was thought to be attributable to the TXV's.

The latter comment (underlined above) is one where a major portion of the issues come from. TXV's only control superheat. Any DX evaporator designed is based on a specific value of superheat to achieve it's rated capacity. If the superheat is too high, the evaporator capacity is decreased. If the superheat is too low, the evaporator capacity can increase slightly.

We already know what happens when the superheat is too low, but in an effort to protect the compressor some will set the superheat too high.

In a lot of applications (mostly medium and low temp) the system actually performs better when the superheat is slightly lower. I almost hate to mention this because of the issues we have with measuring superheat and how the valve should be adjusted.

However, most of you have probably seen a low temp semi-hermetic compressor without any frost on the suction line. You may have also seen some where the suction line had some condensation on the valve. In some instances you may have seen a compressor with frost on the suction valve.


These examples are varying degrees of showing you how the TXV's are adjusted on a low temperature rack/compressor.
The valve that is dry will have a high superheat.
The valve that is wet has a lower superheat (but is probably still too high), while
the valve with frost on it is probably close to being properly set .
The first two are where you can have greatly reduced compressor capacity because the compressor capacity is determined by the gas density (which decreases as the superheat increases). Less dense gas means lower mass flow and that means lower capacity. The compressors will also run hot because the suction gas temperature is too high.

Frost does not mean liquid is present. It simply shows the temperature is below 32°F or 0°C.

Just about every valve I have had to adjust is because someone else adjusted it before I arrived on site. TXV's are adjusted to cure all sorts of problems which are thought to relate to the TXV.

In the end, very few problems can be attributed to the TXV's if they are properly selected, installed and operating under stable conditions.

The problems start after this has occurred.

The superheat should always be checked. It should only be adjusted when someone has verified the TXV is the root cause of the problem and not one thought to be associated with the TXV.

We may have to agree to disagree, but that's OK.;)

[philfridge]

The knob on the side of the valve is there for a reason;)






Andy I have to disagree if you select the correct T.E.V and more importantly the right sized orifice that knob you mention should not be touched. Just because its their you dont have to mess with it :D

[archibaldtuttle]

just renewing the 'put down the wrench and get away from the valve' discussion with a real world test on the trane 7.5 ton circuit mentioned above.
It has a Sporlan XVE 5 (OEM equivalent of SVE 5 aftermarket).

Ran it again yesterday to check conditions before making any valve or refrigerant adjustment.

I had recovered the factory charge still in the circuit into an empty recovery can. Replaced the valve head which had lost its charge. Used an XGA head because the local distributor did not have an XCP-100 in stock.

Replaced the charge fully (obviously filtered in both directions).

turned on most of the fan coils yesterday and good circulation of water through the evaporator.

Here are the results.

Ambient outdoor temps in the low 70s, but this brick building was 10 degrees warmer because the tower had been off and it was hot an humid in the 80s up until a few hours before I got back to this job. Actually went in the morning to turn on the crankcase heater and then went back in the afternoon after some severe thundershowers that cleared the humidity and lower the temperature.

First stable plateau at

170 psi 76.8 F discharge, 54 psi 29.8 F suction, 57.4 F in wat., 53.4 F out wat.

then dropped towards these readings before satisfying my evaporator temp. sensor which is set fairly warm (50 D. F cutout and there is about a 9-10 deg. non addressable differential till cut-in) at the moment because of my low superheat condition and concern about liquid return.

165 psi 74 F discharge, 49 psi 27 F suction, 54 F in wat., 50 F out wat.

So my reading on this is that I have 14 deg. subcooling at the first plateau and finish out with 15 deg. subcooling

But my superheat is barely 2 deg. , not a very comforting place to be sitting.

Unfortunately, for all my careful metering, I forgot to take a careful ambient measure, but I was pretty damn chilly in shorts and T shirt and it might even have been in the upper 60s at that point, but my liquid line temps are getting with 4 to 8 degs of ambient. According to Jim wheeler I could charge this system a little bit more to chase ambient temps. But given that the subcooling is pretty normal and in desired range and I'm still at factory charge, less maybe some bit of an ounce of multiple hose connecting and the like, do these results indicate the possibility that I might have to violate the prohibition on adjusting the TEV? Should I charge a tiny bit and see if I can bring the subcooling down even more and suction pressure up a bit before I consider adjusting the TEV?

Thanks, I'll post the latter part of this post on the TEV adjusting thread we also have running. apologize for redundance, but for those using topics to guide them to information, this question should probably be over there as well.

Thanks,

Brian

There is no excuse for me...
... and there is no such thing as an EXTRA beer

[nike123]

According to Jim wheeler I could charge this system a little bit more to chase ambient temps. But given that the subcooling is pretty normal and in desired range and I'm still at factory charge, less maybe some bit of an ounce of multiple hose connecting and the like, do these results indicate the possibility that I might have to violate the prohibition on adjusting the TEV? Should I charge a tiny bit and see if I can bring the subcooling down even more and suction pressure up a bit before I consider adjusting the TEV?




Prohibition is not in force when you fited new power head. Filing the refrigerant further, will not change superheat, only subcooling.

Cover some part of condenser to get near 100-105°F condensation temperature.

Adjust now your TEV with superheat 4-7K (8-15F)°and then check that subcooling.

[Andy]

Andy I have to disagree if you select the correct T.E.V and more importantly the right sized orifice that knob you mention should not be touched. Just because its their you dont have to mess with it :D

Hello philfridge
if the valve is selected correctly:eek: sometimes a selection falls where two selections will give the required capcity.

One will need the valve opened up to suit the other will require the valve closed in.

Seldom does a selection hit spot on, some adjustment is nearly always needed.

When advising younger engineers I always try to instill the need to check the superheat (and in the case of EEV the valve opening degree).

In my experience most valves are not at there optimum.

But what I will say is it takes years to know when to adjust and when not.

There is no substitute for experience:D

Kind Regards Andy:D

[icecube51]

first of all, take yore time to find out if adjustment is needed,take notes and measurements, if needed be very very careful how to adjust.
it takes time and patience and skill and more time and patience and time.each time you change the not,even for a mil, you have to Wait for the system to be in balance,and then start all over again, till you get it wright.it can be done in 3 hours ore take a hole day.:rolleyes: i suggest they change the name from TEV, to BST, stands for Blood Sweat and Tears, thats why most of them say " don't touch"

Ice

[Kh1971]

Hi,

Main issue that every one is going the easy way to repair so they well say we well adjust the TXV , but no one check what is the problem exactly ..... so please check your problem very well and dont touch the adjusting of the exp valve

[PaulZ]

Another good reference on TX valves can be found on Parker's site.
http://www.parker.com/portal/site/PARKER/
then search Sporlan and under search results click on Literature and read bulletin 10-9.
This site has service bulletins of just about everything Parker and Sporlan make.
Hope this helps.
Paul