Insulating TEVs

[seanf]

Externally equalising TEVs fitted outside the refrigerated space on freezer or chill rooms. Do you insulate or leave them open to the ambient temperature or even hot roof space? Have you seen a difference in operation from being uninsulated to being insulated?

Ive seen a number uninsulated in different situations, on boats and in factories. not as many insulated though.

Thanks

[RANGER1]

seanf,
From my understanding bulb senses temperature, external equaliser senses pressure, so I don't think you have to insulate.
TX bulb obviously would be if outside or in air flow in cabinet.

[seanf]

Hi Ranger,

Im not sure myself, I though I had read it somewhere to insulate the whole valve or just the power element if outside the room.

I would have thought you might get enough heat transfer to the charge if you had say a freezer with the TEV in a hot roof space. But maybe you can just adjust the superheat to accomodate that, if the roof space doesnt get cold during the winter.

Unsure of how much it would affect it, was wondering if anyone had experience of operational changes.

Thanks

[RANGER1]

Seanf,
Car aircon TX valve next to car engine.
Plate heat exchanger TX valve outside in ambient.
As long as it is close as possible to evaporator/distributor.
https://www.parker.com/Literature/RAC%20Division%20-%20Europe/RAC%20Division%20-%20Europe%20-%20Literature%20Documents/Service%20and%20User%20Manuals/10-11TEV-2UKLow.pdf

In link it mentions if tx bulb gets colder than bulb, that it might cause issue.
What problems aren’t you experiencing.

[Tycho]

I'm with Ranger here, shouldn't really matter where the valve is placed (Unless)

I'm going to use Danfoss terms here, TEV = smaller TE valves for like a walk in freezer, no external equalization.
TEX = thermostatic expansion valve with external equalization, used for larger evaporators.

Like I said, shouldn't matter, UNLESS... Unless the valve itself is placed in an environment that has a temperature that is extremely different to the one in the coldroom/freezingroom.

Because this valve is externally equalized to the pressure in the evaporator, and the bulb is filled with refrigerant, what does refrigerant do? it migrates to the coldest place... where is the coldest place? in the bulb that is attached to the suction pipe on the evaporator.

So, the only thing that will have impact on moving the diaphragm in the TEX, is the pressure in the equalizing line, vs the pressure created inside the bulb by the variations of the temperature in the suction line of the evaporator.


Now of course, if the valve is outside the cold-/freezing room and is at +50 degrees, it may be affected.

Luckily, I haven't had to deal with too many TEX valves in my time, but we had one plant where the client demanded that the TEX valves be placed so they could be serviced without the onsite engineers having to go into a -29C crawlspace. the valves were placed in an adjacent crawlspace (-10C, but no fans blowing :)), so they accepted it. we adjusted the super heat across the evaporators and there hasn't been any issue since.

[seanf]

Seanf,
Car aircon TX valve next to car engine.
Plate heat exchanger TX valve outside in ambient.
As long as it is close as possible to evaporator/distributor.
https://www.parker.com/Literature/RAC%20Division%20-%20Europe/RAC%20Division%20-%20Europe%20-%20Literature%20Documents/Service%20and%20User%20Manuals/10-11TEV-2UKLow.pdf

In link it mentions if tx bulb gets colder than bulb, that it might cause issue.
What problems aren’t you experiencing.

Do you get expansion valves with bulbs on cars? only seen the ones with the just the diaphram.

No current problem, was just reminded and wondered.

The concern was mainly from seeing freezer rooms with the valve in what could be a hot or cold roof space, the valve could end up being at a warm roof space temp if theres been a long enough off cycle, it could be clear of or coverded in ice during operation, or ice has covered the diaphram so you could end up with the bulb being warmer during a defrost. And then if it does make a differnence, if you set up the valve during winter would you end up with problems in the summer.

Thanks

[seanf]

I'm with Ranger here, shouldn't really matter where the valve is placed (Unless)

I'm going to use Danfoss terms here, TEV = smaller TE valves for like a walk in freezer, no external equalization.
TEX = thermostatic expansion valve with external equalization, used for larger evaporators.

Like I said, shouldn't matter, UNLESS... Unless the valve itself is placed in an environment that has a temperature that is extremely different to the one in the coldroom/freezingroom.

Because this valve is externally equalized to the pressure in the evaporator, and the bulb is filled with refrigerant, what does refrigerant do? it migrates to the coldest place... where is the coldest place? in the bulb that is attached to the suction pipe on the evaporator.

So, the only thing that will have impact on moving the diaphragm in the TEX, is the pressure in the equalizing line, vs the pressure created inside the bulb by the variations of the temperature in the suction line of the evaporator.


Now of course, if the valve is outside the cold-/freezing room and is at +50 degrees, it may be affected.

Luckily, I haven't had to deal with too many TEX valves in my time, but we had one plant where the client demanded that the TEX valves be placed so they could be serviced without the onsite engineers having to go into a -29C crawlspace. the valves were placed in an adjacent crawlspace (-10C, but no fans blowing :)), so they accepted it. we adjusted the super heat across the evaporators and there hasn't been any issue since.

Cheers Tycho,

Its that difference in temp you could get, much higher than what the valve would deal with being in the room. Diff of 20C doesnt sound too bad when I think about air con, but even just a +20C ambient to a -25C freezer starts to seems alot.

Thanks

[RANGER1]

Do you get expansion valves with bulbs on cars? only seen the ones with the just the diaphram.

No current problem, was just reminded and wondered.

The concern was mainly from seeing freezer rooms with the valve in what could be a hot or cold roof space, the valve could end up being at a warm roof space temp if theres been a long enough off cycle, it could be clear of or coverded in ice during operation, or ice has covered the diaphram so you could end up with the bulb being warmer during a defrost. And then if it does make a differnence, if you set up the valve during winter would you end up with problems in the summer.

Thanks

You are right, was trying to think of example.
PHE one still stands.
We do not have the extremes in climate you do, so different scenario's.
Bulb charge type could be considered.


https://sporlanonline.com/literature/education/10-9.pdf

[seanf]

You are right, was trying to think of example.
PHE one still stands.
We do not have the extremes in climate you do, so different scenario's.
Bulb charge type could be considered.


https://sporlanonline.com/literature/education/10-9.pdf


Car AC is a good one, still thermostatic with big changes in temperatures it could experience.

Aye, seen PHE with and others without insulation on the valve both seeming to work ok.

Maybe it is just careful selection of the valve, cant say Ive look very far into the ones Ive seen.

Another one is TEVs on Frigoblocks, some of there units have uninsulated valves directly in the air off of the condenser.

Thanks

[chemi-cool]

The only reason I insulate TXV that is out side the cold/freezer cabinet is to protect the nut on the TXV outlet from getting moisture in and crack it unless it is brazed one.

Insulation will also eliminate water puddles under the TXV if it is not insulated.

[seanf]

Cheers Chemi

[Glide]

Interesting product related to this topic :

https://www.schiessl-kaelte.com/de_AT/Shop/Montagematerial/Isoliermaterial%20%26%20Brandschutz/Isoliertaschen%20f%C3%BCr%20Expansions-Ventil/Euro-Isoliertasche-weich-f.Expansionsventil-T2-TE2-TI-TIS-TILE~p122604

[Glenn Moore]

This is a very interesting subject Sean ,you should have come to one of my lectures when I was in Scotland most of this was covered,but this is from my 40 years with D&W and Danfoss.
Thermostatic expansion valves come in two types ie Internally Equalised and Externally Equalised, they can be distinguished by the Internally Equalised Valve has only two connections whereas the Externally Equalised Valve has three.
There are 3 forces that allow the TEV to function correctly :-
1) The Tev Bulb. Is the valves sensing element tightly strapped to the outlet connection of the evaporator. The Bulb converts the suction pipe temperature into a saturation pressure equating to the refrigerant type in the system. This Bulb Pressure is the valves “opening force” Pb
2) The Superheat Spring. The superheat spring once set to give optimum stable superheat control is a constant. The Superheat spring is a “closing force” Ps
3) The Equalisation Pressure. (either internal or external ) varies with the suction pressure .The Equalisation Pressure is also a”closing force” Pe So the Spring Pressure (Ps) + the Equalising Pressure (Pe) are the combined closing force pushing on the underside of the TEVs diaphragm, which opposes the Bulbs “opening force “ which is topside of the TEVs diaphragm.
The types of charge in the bulb also has a bearing on the way the Tev functions. In theory the charge in the bulb could be of the same type as in the system .But this is not the case . The charge is designed to give a constant degree of superheat across its working evaporator temperature band ie, once the operating superheat has been set it will be almost the same if it was evaporating at plus 10degC or down at minus 40degC or anywhere in between. This is done by using a mixture of fluids to make up the bulbs charge.
This is why it is not advisable to use Tev designed for a specific refrigerant and then use it in a system with another refrigerant.. ie Using an R22 or R404A valve, on R407F or R407A.
Doing this retro fit always causes the valve to be adjusted to prevent flooding etc. But often the superheat will vary at different evaporating temperatures and often ends up with excessive superheats and hence poor system operation .”Always use the correct Tev for the gas in the system,otherwise fit an electronic expansion valve with the correct refrigerant setting.
Charge types
Universal charge:- With this charge the bulb has a large liquid charge in the bulb, which has enough volume to fill the cap tube and the diaphragm and still have a little left in the bulb for it to function.

MOP charge :- With this charge, the bulb only has a small liquid charge in the bulb, and when all the charge has evaporated, the pressure force the bulb exerts onto the diaphragm is limited qat that point ie its MOP point (Max Operating Pressure ) or as some engineers call it (Max Overlaoad Point)
Danfoss Tevs the N range has a universal charge, Evap +10degC to -40degC
The NM range has an MOP charge Evap -5degC to -40degC
The NL range has an MOP charge Evap -10degC to -40degC
The B. range has an MOP charge Evap -25degC to -60degC

So the TEV charge type is a major factor to its ability to control correctly.

Therefore the control equation to the TEV =

Pb. Opening force
Pe + Ps. Closing Force


So the temperature of the valve body in a roof space etc has virtually no effect on the operation of the valve as the charge that’s in the power element (diaphragm) is only vapour he controlling opening pressure is coming via the charge in the bulb Pb . Some engineers tend to insulate the valve body to prevent moisture dripping as it sweats or defrosts but this has no effect to what the valve is doing.

The problem comes from the other way round. If the bulb becomes warmer than the power element (diaphragm) then the charge can migrate from the bulb into the power element. This is particularly a problem when using MOP valves due to them only having a small bulb charge.
Some years back Swedish Royale supermarket cases came fitted with MOP valves as standard which is ok on a one to system. But the supermarkets then started fitting compressor packs where the need to fit MOP valves was not necessary due to the duty on the packs keeping the system Evap pressures low.
Then they went to hot gas defrost systems but then the problems started. The hot defrost gas heated the suction pipe where the bulb was fitted ,this caused the bulb charge to migrate down the capillary tube into the power element. When defrost terminated and cooling was require the cases just sat ther it’s no gas going into the evaporator's. Often this was diagnosed as ice in the Tevs orifice , and pouring hot after over the valve ould get the valve flowing again. But the actual problem is what is “CHARGE REVERSAL” , this is where the bulb charge has migrated from the bulb to the valves power element.
The solution was to either fit a valve with a universal charge or to move the MOP valves bulb further along the suction line , away from where the hot gas was being injected into the evaporator.
THE BULB IS THE SENSING PART ,IF THE CHARGE MIGRATES FROM THE BULB INTO THE POWER ELEMENT THE VALVE WILL CLOSE
A further instance of this was on some water chillers on a roof in the north of Scotland where during the summer months it worked ok , but come the cold winter months the plant kept tripping on LP . I tested the valves and found no fault with them. But we fitted the two half’s of the polystyrene packing box for the Tevs onto the valves to insulate them and the capillary from the chill winds and we had no further problems. On one very old site which the valves would not operate correctly I fitted short pieces of electric heater tape under the power elements and wrapped some tape to keep the power elements warm to keep the charge in the bulb.

Years back I had a customer who sent back 2 boxes full of TE20 power elements as being faulty and with lost charge. I tested all the valves and they were no fault found. This was again typical symptoms of charge reversal..I went to see the customer and took his valves back, then we went to see the plant.
It was a fish freezing tunnel and it was suffering from poor cooling.it had two evaporators one at the front of the tunnel and one at the back. They cooling was so poor the fish was being put through the tunnel several times to try to freeze it. On measuring the superheat at both Tev bulbs ,the front valve was running with12K superheat and the back one was running with 25k superheat. Both valves were adjusted to give 6k superheat and the tunnel quickly came down temperature as now both evaporators were working .This can be a problem and I’ve seen it many times where multiple MOP valves have been fitted on a plant ,and the valves superheat are set differently, this causes the valves with the lowest superheat setting to become the dominant valve, and the dominant valve causes other valves to become colder than there bulbs and charge reversal starts .

So insulating the power element preventing it becoming colder than the bulb maybe necessary especially if they are MOP type valves ,but otherwise it is not necessary for the valve to function correctly

These days always fit electronic valves as you don’t need equalising lines ,no cap tubes to break or leak,no charge reversal.and lower stable superheat controlling with the correct refrigerant setting in the software, but the best bit is you don’t have to go and freeze your butt off to adjust the superheat it’s done in the warm plant room lol.

[NH3LVR]

Great Info!

[seanf]

Thanks Glenn

[seanf]

A question on Desuperheating valves (TEAT) for you Glenn. I take it its a mainly liquid charge in their bulb/power element?

Thanks

[NH3LVR]

Glenn;
I was having a discussion one time with a friend of mine, which was interrupted and we never got back to it.
He had had experienced problems with TX valves when the liquid was very sub-cooled. I believe this was when the liquid was sub cooled in a two stage system low side and it was feeding a medium temp room at intermediate pressure.
Could you comment on that?

[Glenn Moore]

Sean
The charge in the Teat Liquid Injection Valve has a charge type called Adsorption Charge. Inside the bulb is a piece of brick like material which is porous and acts like a sponge. The charge likes to be encapsulated by the sponge, and as the bulb gets heated the charge is forced out of the sponge to produce the equivalent temperature /pressure in the power element. There is a small pressure equalised bellows to isolate the power element from the internal system pressure so that only the force from the bulb actuates the opening of the orifice.
The latest style of the TE MOP expansion valves also use the adsorption charge ,as this charge is more stable than a pure liquid charge ,as the “sponge “ acts like a signal dampener to slow the reaction of the valve which allows for lower stable superheat settings = more efficiency of the evaporator

[Glenn Moore]

Hi NH3LVR
Subcooled liquid is a very volatile fluid which has masses of energy.
When selecting a TEV for use on a low or medium temperature system that has the liquid supply being subcooled via inter coolers or economisers requires a little more care in the selection of the size of the Tev’s orifice.
Liquid subcooling can be depending on the system design it could be !!!20k maybe 40k or even 50k , but this figure must be in the calculation for the correct TEV orifice size .
So let’s say the evaporator duty is 40kw and the worse case liquid subcooling is 50k on R22
So the correction factor for R22 with 50k subcooling is 1.44
So the 40kw divided by subcooling factor 1.44 = 28.8kw
So the correct selection of the orifice would be one that has the duty of 28.8kw at the design conditions , the orifice which could do 40kw at design conditions would actually somewhere near 40% oversized for the job.
The result would be the the Tev’s orifice would be much to big in capacity and would result in the orifice struggling to control this rampant stream of heavily subcooled liquid.
Typically this size of valve would be in the TE12 capacity size,the diaphragm movement from closed to fully open is just under 1Millimetre .The power in this liquid and the valve trying to close back on its seat trying to control its superheat,can cause the valve to start to literally scream and make a honking sound , the valve and adjacent pipe work will start to jump around violently often causing the pipe work to break etc .
Often the solution is to replace the orifice with a smaller one ,this has the effect of the orifice needing to be well of its seat allowing a less restrictive flow and hence no more noise etc.
The modern solution would be to fit a stepper motor type electronic valves as they have a wide opening degree something around 22miilimetres and therefore a wide capacity band.
When the Tevs are in this oversized heavily subcooled situation the orifice pin is literally banging up and down and the liquid is sending shock waves back along the liquid line to the next valve in the line ,normally a solenoid valve .These shock again smash the solenoid diaphragm up and Down to the point of destruction ..

I witnessed this situation several times and when you see an 15/8” copper pipe whipping across a cold room roof like a rubber hose , then you put on your brown overalls and run away cause next thing you get is a fractured pipe pouring a massive jet of very cold liquid around the room . Not for the faint hearted .
So in TEV Selections on plants with heavy subcooled liquid use the correction factors as it may be a costly oversite

[RANGER1]

Post not relevant

[seanf]

Thank you Glenn

[Tycho]

15477

I have learned more about TX/TEX and TEAT valves in this post than I have in school and 24 years in the field!

This was really interesting stuff, even though it is not something I usually work with!

Well except the TEAT valves that we use on LRI systems on screw compressors to maintain discharge and oil temperature on certain plants.

When I was in school, back in.. umm, '94-95, and we were taught about TX/TEX valves, the teacher told us that inside the bulb/sensing element was a small charge of the same refrigerant that the valve was designed for.

So if the valve was designed for R-22, the sensing element would therefore have a small charge of R-22 in it.

Also, in my previous post, where I said that if the valve itself were placed in an environment that were extremely warmer than the sensing element (diaphragm), I can see it makes no sense now that Glenn Moore has explained, it should be self explanatory really, expansion and contraction.


I just learned something, I'm going to have to re-read this thread a few more times before I can understand it and be able to pass it on though :)


But I have a saying that I tell all my guys "if you ever find yourself, confidently telling yourself, that you now know everything there is to know about Refrigeration", then you should start looking for a new line of work :)

:)

Glenn Moore, I weren't able to put it in my reputation note, but you are a man of my own heart! Long posts, sharing knowledge and experience :)

My posts are long, and I share my knowledge and experience, if I am correct, I don't know :)
If I am correct 50% of the time I will be happy :)

[Glide]

Charge types
Universal charge:- With this charge the bulb has a large liquid charge in the bulb, which has enough volume to fill the cap tube and the diaphragm and still have a little left in the bulb for it to function.

MOP charge :- With this charge, the bulb only has a small liquid charge in the bulb, and when all the charge has evaporated, the pressure force the bulb exerts onto the diaphragm is limited qat that point ie its MOP point (Max Operating Pressure ) or as some engineers call it (Max Overlaoad Point)


Great post Glenn. I was unaware that all liquid evaporates. I always thought there should be some liquid in the bulb so that the content of the bulb is always in a saturated condition.

Could you share some knowledge about the TXV's for the high glide refrigerants like R448A, R449A etc.?
Where there is no glide, the pressure that the bulb exerts corresponds to the bulb temperature (i.e. the saturation temperature). But when we're dealing with high glide refrigerants, what is the relationship between bulb temperature and the pressure that it exerts?