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I was hoping that someone could explain in simple terms how a basic expansion valve works! also with respects to the equalising line, when it is needed and when to use internal equalising valves.
Also why when condensing fans start does the sight glass in a liquid reciever become cloudy?
Thanks alot!
The expansion valve meters the liquid ***** into the evap. It lets little enough ***** into the evap that the evap has low pressure. (The fact that the compressor is sucking ***** out of the evap at the same time helps too.) Low pressure evap can boil ***** at a low temp to cool your space.
Bubbles in the sight glass is a good thing when the fan comes back on. It has to do with the change in pressure and subcool. I think that the pressure drops so fast before dropping the temp that your subcool dissapears for a few seconds.
Now that I put my neck out on this, somebody will come along and fill in the gaps and explian where I am wrong or, as I like to say, a little misleading. We all know that I am seldom wrong, maybe not exactly correct, but close enough to not be wrong either.
The Prof might suggest the following Sporlan bulletin on TEV operation: http://www.sporlan.com/10-9.htm , and not simply because he wrote most of it... :)
A thermostatic expansion valve (TEV) regulates refrigerant flow thru the evaporator by maintaining constant superheat at its sensing bulb location, which is normally located at the evaporator outlet. By maintaining constant superheat, the TEV can keep the evaporator surface as fully active as possible under varying loading and operating condition, at least when compared to a cap tube or restrictor which are often used on residential a/c and small refrigeration units.
There are three fundamental pressures that affect TEV operation. Sensing bulb pressure is a function of bulb temperature, and it acts on the valve in an opening direction. Conversely, equalizer and spring pressure work together and act on the valve in a closing direction. The bulletin goes into detail on this subject.
An internally equalized valve should only be used on small capacity, single circuit evaporators where pressure drop across the coil is negligible. Otherwise, an externally equalized TEV should be used. You can always use an externally equalized TEV.
The fact that the sight glass will often show flash when a condenser fan comes on via fan cycling control is due to the ensuing drop in head pressure. This drop in pressure lowers the saturation temperature in the receiver a bit, causing flashing. But equilibrium should be regained in short order, thus clearing the sight glass.
Can you define small capacity please?
Also, I want to change a window a/c unit from cap tube to TEV. It's a 9600 to 10,000 btu 110volt unit, R22. Is it worth the effort?
Can the same TEV work on a/c's as small as 8000btu units or does it need something different?
I wanted to experiment on 8000, 8500, 9000, 9400, 9600, 10000, 12000, 15000, 18000, ans 20000 btu units.
You got a 'fitz-all' TEV? LOL
PS on externally Equalized TEV's, do I have to connect a line from the TEV to the evaporator discharge to equalize pressure?
I am getting a little confused on internally equalized and externally equalized.
Also, if I used a TEV that was too big, what would be the consequences?
Probably not. But you would certainly impress the Prof if you did so! :)Quote:
Also, I want to change a window a/c unit from cap tube to TEV. It's a 9600 to 10,000 btu 110volt unit, R22. Is it worth the effort?
Absolutely! The reason one doesn't see many 8000 btu/hr a/c TEVs is they are difficult to cost justify.Quote:
Can the same TEV work on a/c's as small as 8000btu units or does it need something different?
Not quite :), but it should be just as easy to select the proper TEV size for the coil.Quote:
You got a 'fitz-all' TEV? LOL
The function of an external equalizer is not to equalize system pressures. One would need a TEV with a bleed port for that purpose, or a similar feature, e.g., Sporlan's RPB (rapid pressure balancer).Quote:
PS on externally Equalized TEV's, do I have to connect a line from the TEV to the evaporator discharge to equalize pressure?
The external equalizer simply allows the TEV to sense proper suction pressure for superheat control, and ideally, should be connected to the suction line immediately downstream of the sensing bulb.
An internally equalized TEV senses suction pressure thru an internal passage within the valve, and therefore, senses pressure at the TEV outlet. Internally equalized valves are only suitable for single circuit evaporator coils having low pressure drop.
Poor superheat control/hunting. Keep in mind the function of the TEV is simply to control superheat.Quote:
Also, if I used a TEV that was too big, what would be the consequences?
Prof, would perhaps an answer to "the result of an oversized expansion valve", be; The coil temperature (S.S.T.) will balance at a higher temperature (pressure) than proper design or selection would dictate?
oversized TEV would hunt and possably flood the compressor.
I put a TEV on a 15,000 BTU window shaker one time. It was not that bad. I had parts laying around and time on my hands.
What TEV would you suggest Professor?
Line sizes on the evaporator are about 3/8" in/out (after cap tube).
If I had a part number, I could buy one easily. Without a #, they have to look it up by application, which doesn't list a/c's that small.
Thanks
Johnstone supply lists several Danfoss TEV's, but all of them are rated -20 to +50 deg F.
Any rated +32 and up?
Yeah, Prof. Wanna give him a Danfoss number? LOL
LOLOLOL
Not what I meant Gary.
Johnstone doesn't list Sporlan parts. I wanted the Sporlan part number so I could go to S.W.H. and get the good one!
LOLOL
Quote:
Originally posted by zolar1
Johnstone supply lists several Danfoss TEV's, but all of them are rated -20 to +50 deg F.
Any rated +32 and up?
-20 to +50 means the valve is appropriate for any application wiithin that range (including your 32F up inquiry). You would select a configuration that is rated for the system capacity at the desired conditions.
In the Sporlan department, for you 8,000btu/h to 10,000btu/h application, I would recommend a Q-type valve utilizing a #1 cartidge with a KT43VGA thermostatic element (R-22).
Q-1-VGA
If utilizing external equalization - QE-1-VGA
You can choose the valve body with the pipe connections that you desire. Usually the wholesaler will be glad to assemble the parts for you.
If you do this, you will likely have to put a "hard Start" kit in your compressor circuit to enable the compressor to start up under pressure difference between discharge and suction, because the TEV won't equalize as the cap tube would. Say the T-03 hardstart kit thingy you can get at Johnstone.
:)
The smallest capacity R-22 a/c TEV which a wholesaler would stock would probably be 2 ton.
As a result, the Prof agrees with herefishy's recommendation, and suggest using the Sporlan Type Q series TEV, which employs a replaceable cartridge and replaceable thermostatic element. The valve is available in either SAE flare connections (Q valve), extended ODF connections (EQ valve) or ODF connections with a forged inlet and replaceable strainer (SQ valve)
For R-22 a/c, the #1 cartridge is rated at 0.75 ton, #2 cartridge at 1.0 ton, and #3 cartridge at 1.5 ton.
And as herefishy recommends, you would use the Sporlan KT-43-VGA thermostatic element for R-22 a/c applcations.
You can download product literature from here:
It would appear herefishy is ready to become a Sporlan product manager... :)
Quote:
It would appear herefishy is ready to become a Sporlan product manager... :)
I have been considering getting a real job, lately..... :)
Thank you for the quick replies.
Suppose I wanted to change from R22 to R134a (unlikely) or R502 or R404A. Will I be able to get cartridges suitable for those as well?
Why not simply adjust the TEV instead of cartridge changes?
Regarding the Hard Start - I feel this would be unnecessary because a window A/C fan continuously blows air over the evaporator, thus keeping the heat input constant. The TEV should sense the temperature change and open on it's own, regardless whether the compressor is running or not.
I do wonder if I need a receiver though......
ps....maybe a hysteresis loop comes to mind?
pps..would I need some 'virgin flux' too?
ppps....lol....had to get herefishy to lighten up. I can't imagine him working at McDonald's.........:D
I worked on a Traulsen two door, upright refrigerator today. It had a Sporlan BIJ 1\8 tev on it without a reciever. I needed to replace the valve, my supplier is unfamiliar with this valve, as am I. The refrigerator has a 1/3 h.p. compressor. I replaced the valve with a EFF 1/4 C. Am I correct in assuming the 1/8 on the original TEV is for 1/8 ton? If so am I oversized? I am experiencing some hunting, about 9 degrees of superheat.
Yes, you make'm big BooBoo!!
Obtain the OEM valve from the Traulsen parts distributor (preferrably before the customer gets mad because he lost his food, or the compressor takes a dump!).
:)
Low side:
evap air in temp
evap air out temp
SST
suction line temp at evap coil
suction line temp at compressor
High side:
cond air in temp
cond air out temp
SCT
liquid line temp at cond
liquid line temp at TXV
(I keep thinking someday someone will give us enough information to do it right.)
Well Gary, when the fellow says he removed a 1/8 and installed a 1/4, I say I have enough information....LOL ;)Quote:
Originally posted by Gary
(I keep thinking someday someone will give us enough information to do it right.)
Maybe. Maybe not. Remember this system has a 1/3 hp compressor. :)Quote:
Well Gary, when the fellow says he removed a 1/8 and installed a 1/4, I say I have enough information....LOL
Without the information, we are guessing at the most likely problem, and assuming there are not multiple problems.
The first "guess" is that the TXV needed to be replaced.
Professionals shouldn't guess.
I should point out that I don't mean this as a criticism of any particular person.Quote:
Professionals shouldn't guess.
I have spent most of my adult life trying to find ways to take the guesswork out of trouble shooting. I tune in to HVACR sites all over the net and what do I see? Guesswork. It's discouraging.
Doing it right requires taking a few more measurements, but it is infinitely more accurate.
Most small capacity self contained refrigeration systems that do not employ head pressure control can generally get by without a receiver.Quote:
I worked on a Traulsen two door, upright refrigerator today. It had a Sporlan BIJ 1\8 tev on it without a reciever.
The Sporlan BI series TEV is an OEM style valve, normally supplied non-adjustable.Quote:
I needed to replace the valve, my supplier is unfamiliar with this valve, as am I.
Yes.Quote:
The refrigerator has a 1/3 h.p. compressor. I replaced the valve with a EFF 1/4 C. Am I correct in assuming the 1/8 on the original TEV is for 1/8 ton?
Perhaps a bit. But the EFF-1/4-C is an adjustable valve, and one could expect it to control reasonably well on an application such as this with the proper setting. Getting the proper setting on a TEV that is oversized somewhat, however, will be more tedious than with a valve properly matched to the system's design capacity.Quote:
If so am I oversized?
The Prof would have used an EFF-1/4-C in this situation, assuming the wholesaler did not have an EFF-1/8-C in stock.
What are your high and low values of superheat? What is the approx time it takes for the superheat to go from its low value to its maximum value and back to its low value? Is the evaporator coil top or bottom feed?Quote:
I am experiencing some hunting, about 9 degrees of superheat.
I would like to apologize for making a post without posting all the required information. Thank you to all that replied, you are a great help in my desire to better myself and at the same time to give up.:) :(
It is a top feed coil, with a high of 10 degrees and a low of 2 at it's outlet. The swing takes about 3 minutes in total.
A top feed coil should help here, as you should not have refrigerant trapping in the coil during operation. A three minute lag time is quite long, however. Is it possible refrigerant is trapping in the suction line ahead of the TEV sensing bulb?
Adjusting the TEV may help settle the hunt. Interestingly, you may have better luck settling the TEV here by adjusting it out, i.e., lowering superheat. Or going to a 1/8 ton TEV... :D
I think I would want to check several things before I messed with the superheat, primarily evaporator airflow, condenser airflow and subcooling.
Insufficient airflow through the evap reduces the load, in effect making the TXV even more oversized. When the valve swings open, high head pressure can force more refrigerant through faster, before the valve can react.
Correct me if I'm wrong here, Prof. :)
Everything is connected to everything and everything effects everything.
Thanks professor. I was really tight for time on this job. I was working on two other boxes at the same time. The reason they called us about the traulsen was that a customer had got sick from the food. Apparantly they bought the unit second hand and they never saw it get below 55*. From what I could make of their limited English, they owned the unit for about two months. The unit was not low on gas, but It was 6" in vacuum. I came to the conclusion that the tev had either lost its charge or it had become clogged. I've run into many clogging problems with POE oil. I had to hustle on this one. It could have been moisture frozen in the valve, loss of charge or restriction. Seeing that I wouldflatten most of the evap fins and dice up my hands trying to get wrenches on the valve, I needed to remove it anyway (very tight area). I would rather replace it. My supplier does not carry 1/8 ton valves, but, he tells me, a 1/4 should work. So I tried it. Live and learn, but at this rate, I better live to 105! Anyway, I took apart the old valve and I don't see any restriction. This is where my inexperience is going to show again. Besides not flowing any refrigerant, how can one tell if the head of the valve has lost it's charge? Seeing that hindsight is 20/20, I am leaning towards re-installing the old valve with a new head. I'll be sure to get all the info upon my return to this unit.
If the TEV is rated for 1 ton Nominal, can it be used for 3/4 to 1 ton systems?
The a/c's I want to experiment with are usually 8500 btu and 9600 btu.
My goal is to have an a/c that puts out a constant evaporator temperature, preferably 35F, but no higher than 40F.
The cap tube system that they currently employ varies in temperature from 40F to 55F.
I even thought of trying R408A to see if I could maintain the desired temperature. I was told that R408A is not as efficient as R22.
What is more efficient than R22?
R502? R407B/C?
LOL!!! Of course you are correct. But like many technicians, the Prof will attempt to identify a problem without the benefit of knowing all the parameters.Quote:
Correct me if I'm wrong here, Prof. :)
If you have a TEV with a removeable thermostatic element (power head), you can remove the element from the valve and press down on the diaphragm (where the pushrods meet the element) with your thumb. If the element is dead, you will be able to move the diaphragm. If you cannot move the diaphragm, the element is likely ok.Quote:
Besides not flowing any refrigerant, how can one tell if the head of the valve has lost it's charge?
It is best not to rely only on the TEV's nominal rating when sizing the valve. This is particularly true with refrigeration applications. Far better to check the ratings table for the TEV with the system's capacity, and select the smallest valve that will handle the system's normal operating conditions.Quote:
If the TEV is rated for 1 ton Nominal, can it be used for 3/4 to 1 ton systems?
Look, first of all the real answer to proper repair of the machine is to obtain the original part from the manufacturer. NOW, if someone gets sick from the food with the wrong TEV in it.... who's responsible?
Was the element on the TEV rusted? That is most common cause of failure, is the deterioration of the element body causing the charge to be lost. If the suction was in a vacuun, is there any evidenc of a refrigerant leak? If the unit has a condensate pan loop in the discharge line, that is the most likely location for a leak.
The system is likely rated for about an 15F to 18F TD or 20F to 23F suction temperature. If we assume R-134A @ a 20F suction, we would have a capacity of about .15 Tons, or 1,800 btu/h. the 1/4 under the same conditions is indicated as a capacity of .35 tons or 4,200 btu/h !!!! :(
I'm sorry........ I just looked at these figures, and the only thought that I have is how many other people are going to get sick... before the compressor dies a horrible death. :rolleyes:
It seems that if you "squeezed the valve down" to a proper suction temperature, what would your superheat be? You would essentially be starving your evaporator as the superheat increases, so how much will you be derating your evaporator (or the system for that matter)? What will your entering gas temperature at your compressor be? blah, blah, blah....
It has been my experience that an oversized valve will "work for awhile", perhaps even a year. But then it goes to hell. That's usually when I come into the picture and take the 1/4 valve out, and install the mfgr OEM valve. The sad thing is, I get the grief from the customer about the bill, when it was the Cheapo Service Company that created the problem in the first place. :mad:
The counterman at the supply house is usually not an accurate source of information for particularly TEV application. I don't rely on any counterman! I heard them mislead everyone, particularly in the Sporlan balanced port department, where the box says for "1/2 through 13 tons". Wow! that valve does it all !!! I only need one valve on my truck !". ...... give me a break.
If you are really inclined to trunk-slam this thing, and at least be in the ballpark, fit a "Q" with an "0" orifice (.24 tons). That's about as close as you will get if your rummaging the supply house shelf.
Why would the sales counter be unaware of this potential application... forget it, I know. :p
....there, I've got it all out of my system........ :)
i dont know much about TEV's,but ill thrown in my own $0.02... Window airconditioners probably wont be helped by a thermostatic expansion valve, because the cap tubing is matched to the compressor.Quote:
Originally posted by zolar1
Can you define small capacity please?
Also, I want to change a window a/c unit from cap tube to TEV. It's a 9600 to 10,000 btu 110volt unit, R22. Is it worth the effort?
Can the same TEV work on a/c's as small as 8000btu units or does it need something different?
I wanted to experiment on 8000, 8500, 9000, 9400, 9600, 10000, 12000, 15000, 18000, ans 20000 btu units.
You got a 'fitz-all' TEV? LOL
TEV's are almost required in automobiles to make the airconditioning work. How often do you drive your car with a constant engine rpm? think of what your window airconditioner would work like if the compresssors Rpm's were going from 800 to 5000 all of the time (well, not all of us drive like that). (i dont know about other people, but my cars AC compressor runs at over 2x the speed of the engine. the pulley on the compressor is much smaller than the one on the vibration damper)
My land yacht has a 6 cylender compressor, mounted to a 425 V8. My airconditioning system is supposed to be near 40,000btu's. Without the TEV, i would have better luck with a window unit strapped to the passenger door. Its better to visualize it as a water faucet, and a very powerfull waterpump. if the waterpump is a piece of crap and keeps changing RPM's, your water flow will drop and raise, lowering and rasing pressures, or in this case rasing and lowering evaporator temperatures and load. without that water faucet their isnt any way to regulate flow.
does this make any sense? if not, "you get what you pay for" and that was my $0.02.
The Prof remembers being told of a test performed by one of Sporlan's lab techs in the 1970s where he replaced the TEV used on a Carrier R-22 5 ton residential a/c unit with an OVE-70-GA. This test was done in the early days of the Type O valve, and the tech was curious to find out if he could get the system to work properly with a very oversized TEV. Interestingly, he was able to get the unit to operate properly, set the TEV, and get it to control superheat.
NOTE: please do not do this in the field... :)
Herefishy is correct in that your safest bet is to obtain the replacement TEV specified by the OEM. This is more true for refrigeration systems that are more critically designed, e.g., ice cubers. But most systems can handle some leeway in this area, particularly if the mechanic understands how to check the system for proper operation.
Well, this thread has digressed a little from my original posts.
I wanted to experiment with a window a/c (2 or 3 of them) and expansion valves.
I wanted to see if I could make the evaporator a constant temperature under varying load conditions.
An adjustable TEV would be of great value. I could set what I needed for a partictular unit.
Say a TEV rated for 3/4 ton or 1 ton, and adjust the TEV for a partictular application.
I figured a little Crisco© oil might keep the rust away!
(:p at herefishy...he he)
But seriously, all experiments have to start with an idea and the motivation to at least try.
Sure the window units are small, but they are MUCH cheaper to experiment with than something a lot larger and more expensive. If I break one, I'm only out a hundred bucks or so.
(*hint* zolar has something bigger in mind...;) )
Who knows...maybe the Professor will profit from this, and herefishy might get that TEV rated from 1/2 ton to 100 ton!
You are barking up the wrong TEV.Quote:
I wanted to see if I could make the evaporator a constant temperature under varying load conditions.
Try someting more EPRopriate.:)
]If you are ever in CT, I'll let you know where not to eat.Quote:
I'm sorry........ I just looked at these figures, and the only thought that I have is how many other people are going to get sick... before the compressor dies a horrible death.
angryk, whenever you are in Austin, we'll exchange notes !!!! LOLQuote:
Originally posted by angryk
If you are ever in CT, I'll let you know where not to eat.
A little regress regarding the bad food responsibility comment.... of course, it is the responsibility of those who take the food out of the 70F heater... I mean refrigerator !!! LOL But the tech always gets the grief. ;)
I had a technician (who is truly a master) who, after 2-1/2 years of employment, recently quit :( He gave me 4 weeks notice, and during that 4 weeks, I even gave him a long awaited raise. He said that he liked working for me, and generally liked the job..... But said, referring to the restaurant customers, "I'm sick of the stupid people in/and the filthy f****ing restaurants!!!". :eek:
It seemed that I didn't have enough semi-conductor burn-in chamber, supermarket, soap-cooling tunnel and industrial air-dehydrator/tool-cooling jobs to satisfy his need for peace and harmony on the job. :(
Anyway, Zolar..... go for it..... We didn't mean to digress but, "You haven't gotten that TEV installed yet?"
Do it to it....... and let us know how it comes out...!!!!!!!! ;)
What did the Prof (and I) suggest, a "Q" with a #1 orifice?
A TEV only has ONE capacity under any particular condition. Forget this concept about "well it's good for this or that". Expect more of yourself!!!!! The capacity of the TEV (or any expansion device) is based on the volume of refrigerant that will "go through the little hole" relative to the density, enthalpy, and pressure (drop) across the refrigerant control device under the given or (desired) conditions.Quote:
Say a TEV rated for 3/4 ton or 1 ton, and adjust the TEV for a partictular application.
Control the application..... Do not let the application control you!!!! Consider the conditions that are anticipated, determine what you want to happen under those conditions, and make the best selection accordingly. Closing your eyes, picking a valve up off the shelf and applying it to "see what happens", or "what I have to do (to make it work)", is bass ackwards!!! That is the application controlling you.
Who's the master? The man, or the machine?
:)
I don't know what you have in mind, but it occurs to me that a device which likely is a true variable application EXPANSION DEVICE would be an electronic EEV (such as that produced by The Prof - perhaps others?) that I believe uses a "stepper" type control circuit to control refrigerant flow (such as the "stepper" type EPR's which I understand are a very successfull product line in the supermarket market).Quote:
Who knows...maybe the Professor will profit from this, and herefishy might get that TEV rated from 1/2 ton to 100 ton!
You'd better do a patent search first, Zolar1. :)
Prof, why would the manufacturer not endeavour to promote the proper application of their product? Much energy and research must be expended in producing the tables and software for determining a proper valve selection. I say that this is not for NOT!!! Because I see the effects of the misapplication and misconceptions of this component, to the extent that I rely on it (the misapplication) for much of my livelyhood!!!! To say that a 70 ton(nominal) valve (which essentially means nothing.... because a valve with the number "1/4" on it could mathematically provide such a refrigerating effect under prescribed conditions) be proclaimed to do the job in a 5-ton application, I think absurd!!!!Quote:
Herefishy is correct in that your safest bet is to obtain the replacement TEV specified by the OEM. This is more true for refrigeration systems that are more critically designed, e.g., ice cubers. But most systems can handle some leeway in this area
Respectfully posted.........:)
Mmmmm... let's simply say physics would prevent a TEV rated at 1/4 ton per ARI Standard 750 to flow anywhere near the equivalent of 70 tons, regardless of the operating conditions... :)Quote:
To say that a 70 ton(nominal) valve (which essentially means nothing.... because a valve with the number "1/4" on it could mathematically provide such a refrigerating effect under prescribed conditions)
Basic TEV sizing, as taught in TEV sizing 101, states to use a valve that has a capacity no larger than necessary. This is good advice, and it keeps folks who understand how to do basic valve sizing from getting into trouble. But it hardly means that a system designer or refrigeration mechanic should never use an oversized valve for an application.Quote:
be proclaimed to do the job in a 5-ton application, I think absurd!!!!
Consider an R-404A 6000 Btu/hr freezer operating at a –20°F evaporator and normal head pressures. A Sporlan Q valve with a #2 orifice is perfectly adequate for the design conditions. But let’s say the freezer is connected to a compressor rack, and it is desired to have the freezer pull down to temperature as fast as possible following a defrost. And let’s say the load on the coil following defrost will reach as high as 18,000 Btu/hr as the compressor capacity is available to achieve the coil TD for this load. So what is the correct TEV size for this application? A #2 orifice is adequate for the design conditions, but it will clearly cause the TEV to starve following defrost, and thereby lengthening pulldown time. In fact, a #5 orifice would be necessary to cover the pulldown load. Would it not be better to bump the Q valve orifice sizing to a #3 in this case?
Oversizing mechanical TEVs has its obvious limitations. The primary problem: the more oversized the TEV, the more difficult it becomes to adjust.
Oversizing step motor electric expansion valves (EEVs) is less of a problem, but that’s another subject. :)
The professor reminds me of Columbo the detective who leaves the room and turns back and says...Quote:
Oversizing step motor electric expansion valves (EEVs) is less of a problem, but that’s another subject.
"One more question.":)
Thanks for the support and feedback.
That'll be $1.00 for that double cheezeburger pwleeze.....LOL
Well, I have been busy lately and still haven't had time to play with my project.
Regarding a patent search.....since the idea I have in mind isn't sold by anyone, it's quite plausible to assume that there is no patent on the idea. I want to see if it works first, then check for a patent. No infringement worries since I won't be selling anything. To bypass a patent, I was told you only have to change something by at least 20% to be allowed to apply for a patent.
No hurry here though. No money to pay for patent attorney..sigh
I wonder how many really good inventions were lost due to inability to PAY for a patent search and attorney?