Internally equalised TEV

[get the gauges]

I'm on a job, a chill room, a 15 deg c room and a -24 room . All T'd off a main run of pipe work connected to an unloading bock vee configuration compressor which stays unloaded most of the time as it's mainly the the freezer that calls most. It's foreign installed on a vessel,but i've got a query has anyone ever seen people put internally equalised valves on coolers with distributors before as i was under the impression that they were for small kit . All these coolers run alco internally equalised valves and seem to have no probs.:confused:

[monkey spanners]

I've seen it done and have changed them for external valves as the system was experiencing flood back problems. It was a R404A valve but someone had writen "adjusted for R22":eek::confused::mad: next to it with permanent marker so i changed the refrigerant too:p

I think the idea is that if the evaporator outlet pressure is going to be within a couple of psi then internal is ok, but if a distributor is used or the evaporator is in other ways restrictive it needs an external valve. If in doubt fit an external.

I've also seen external valves with the equalising connection caped off:confused: not working as they should

Jon

[Chunk]

http://www.refrigeration-engineer.com/forums/showthread.php?t=2744&highlight=expansion+valves I thought i had seen this asked before.:)

[NH3LVR]

Sometimes we have to say "If it ain't broke, don't fix it.)
I have allways thought no harm could come from installing a External Equal Valve, even if not required.
I would not consider using a Internal Equal Valve with a distributor. Sporlan says no, but if it works OK, leave it.

[powell]

I'm on a job, a chill room, a 15 deg c room and a -24 room . All T'd off a main run of pipe work connected to an unloading bock vee configuration compressor which stays unloaded most of the time as it's mainly the the freezer that calls most. It's foreign installed on a vessel,but i've got a query has anyone ever seen people put internally equalised valves on coolers with distributors before as i was under the impression that they were for small kit . All these coolers run alco internally equalised valves and seem to have no probs.:confused:
The rule is to not use an internally equalized TEV if there is pressure drop in the evap coil. This obviously is to help read the true superheat at the outlet of the evap. In my experience, really old system (the 1960's) used internally equalized valves, maybe because of old technology. But we now know to use externally equalized valves when there is a pressure drop.

[get the gauges]

Thanks for the replies ,i'm going to change 'em all any way, the freezer gets down to -20 pretty quick but takes ages to get from there to -25 i've got to rule out the valve.

[NH3LVR]

Thanks for the replies ,i'm going to change 'em all any way, the freezer gets down to -20 pretty quick but takes ages to get from there to -25 i've got to rule out the valve.
It cannot hurt to change them out, if the expense is not a problem.
Another thing I have seen is if the wrong powerhead is installed. The room came down at first just fine, then just stopped. If that were the case and you left the original valve in and changed the powererhead you could run into problems.

[nike123]

Thanks for the replies ,i'm going to change 'em all any way, the freezer gets down to -20 pretty quick but takes ages to get from there to -25 i've got to rule out the valve.
You could do that by measuring capacity of evaporator without change of TEV. If capacity is lower than it should be then change TEV. Just my 2 cent's.

[get the gauges]

You could do that by measuring capacity of evaporator without change of TEV. If capacity is lower than it should be then change TEV. Just my 2 cent's.

Ok, how exactly do i measure the capacity of the evaporator.What would be the procedure ? I can feel a nugget of useful info coming !

[nike123]

Easiest is by entering required data in to software like this:
http://farm4.static.flickr.com/3091/2285856316_73dab364f9_o_d.jpg

Measure air flow or find in catalog, measure air in/out temperature/humidity and enter in this software.
http://fridgetech.com/software/files/SIahuCalc3.zip

Or if you have palm you have palm version.

Take measuring after some time after defrosting of coils.

[Gary]

Thanks for the replies ,i'm going to change 'em all any way, the freezer gets down to -20 pretty quick but takes ages to get from there to -25 i've got to rule out the valve.

All TXV's will run wide open when the sensing bulb is warm (during pulldown) acting just like a fixed orifice system. It isn't until the refrigerated space is close to it's design temperature range that the valve starts modulating. That's when having the correct TXV makes a difference.

[get the gauges]

Measure air flow or find in catalog, measure air in/out temperature/humidity and enter in this software.
http://fridgetech.com/software/files/SIahuCalc3.zip

Or if you have palm you have palm version.

Take measuring after some time after defrosting of coils.

I'll have a go at taking the those readings next time i'm scratching my head,thanks.Not that i usually take RH readings or air flow ,i think generally people just have a look at the fan and check it's on,am i alone there coz i've never seen a whirling psychcrometer in anyone's van i know of,or an anenometer for that matter.

[get the gauges]

Here are the results from my tests.

unloading compressor runs at about 12 psi when all 3 rooms are down to temp but this 3rd room struggles to get to from -20 down to -23 unless left for many hours where i have seen other rooms get down in less than 20mins. The condenser/receiver is a water cooled bitzer type,long green sausage with a liquid level sightglass.
water on = 10 degC
water off = 18 degC
HP R404a = 271 psi = 42degC
LP R404a = 12psi = -33degC
Discharge temp 80+ degC
Liquid line temp = 30degsC
suction temperature at the evap = -20degC sometimes going to -24 for maybe a minute but then coming back up to -20.
TEV bulb is fixed at the 3 o'clock position on a 7/8" pipe. But was originally sat at 12 o'clock but i moved it.


When the unit runs the liquid sightglass is full but the liquid level sightglass on the receiver is showing over half way above the glass (it sometimes goes above the sight glass but we are on a ship and the weather was a bit rough that day). There is an identical 100% standby system that when running keeps it's receiver well drained with the same amount of gas in it's system.This system is also slow at getting from -20 to -25degC but does it many times quicker than the first system i have described, with same TEV set up .

Does it look like the valve is just not letting much refrigerant through when it reaches -20degC and backing the liquid up in the tank.How can it get to -20 but not want to go the rest of the way,it's got a low back pressure to evaporate in to . Blooddddyy freezers!!!!!!!!!:confused:

[Gary]

I'll have a go at taking the those readings next time i'm scratching my head,thanks.Not that i usually take RH readings or air flow ,i think generally people just have a look at the fan and check it's on,am i alone there coz i've never seen a whirling psychcrometer in anyone's van i know of,or an anenometer for that matter.

I have been known to wrap wet toilet paper around a temp sensor. Does that count?

[Gary]

water on = 10 degC
water off = 18 degC
HP R404a = 271 psi = 42degC
LP R404a = 12psi = -33degC
Discharge temp 80+ degC
Liquid line temp = 30degsC
suction temperature at the evap = -20degC sometimes going to -24 for maybe a minute but then coming back up to -20.


Your superheat is 13K. That's much too high. Since there is plenty of liquid available and the pulldown is quick we can assume the orifice is large enough and that there are no restrictions. Also, it appears that the valve is modulating (enough refrigerant flow to cool the bulb). So that brings us to TXV superheat adjustment.

Open the TXV one full turn, wait a while then take new measurements.

[Gary]

Hmmm... Wait... Where are you measuring the suction pressure? If there is an EPR valve in the suction line we need to know the pressure on the evaporator side of the EPR.

[get the gauges]

[quote=Gary;94356]Hmmm... Wait... Where are you measuring the suction pressure? If there is an EPR valve in the suction line we need to know the pressure on the evaporator side of the EPR.[/quote

There's no EPR on this cooler but there are on the two other higher temp coolers on the circuit. I'm measuring the suction at the cooler outlet. And i've tweaked the valve out bit by bit. With no joy. Just remember that these distributor coolers have been fitted with internally equalised valves,as i originally queried.One thing i didn't check was the orifice size although as i say it does pull down ok. Thanks steve

[nike123]

I'll have a go at taking the those readings next time i'm scratching my head,thanks.Not that i usually take RH readings or air flow ,i think generally people just have a look at the fan and check it's on,am i alone there coz i've never seen a whirling psychcrometer in anyone's van i know of,or an anenometer for that matter.

If you are sure that fans works Ok, you could use nameplate/catalog data for air flow.
For humidity, just wrap piece of wet cotton lint around thermometer tip, and allow some time to measure wet bulb temperature.

[Gary]

Warm the sensing bulb (I just hold it in my hot little hands). This should cause the coil to flood. If it doesn't, then adjusting the superheat isn't going to do anything.

This would tell us that insufficient liquid is reaching the TXV inlet (undercharge/restriction)... or the inlet screen is plugged... or the orifice is undersized. Most likely would be a plugged inlet screen.

On the other hand, if warming the bulb floods the coil then the TXV needs to be adjusted.

[Gary]

Just remember that these distributor coolers have been fitted with internally equalised valves,as i originally queried.

The pressure drop through the distributor itself is substantial and any coil with a distributor should have an externally equalized valve. That said, an internally equalized valve can usually be made to work.

I am assuming that this system was initially able to work properly despite the internally equalized valve.

At this point we are determining whether sufficient liquid is reaching the TXV and if its orifice is large enough.

No doubt it would perform better with an externally equalized valve (modulating more accurately), but not if there is a restriction in the liquid line or if the TXV orifice is undersized.

[Gary]

Here is something more for you to worry about... distributor nozzle sizing:

http://www.heatcraftrpd.com/resources/techtopics/Tech%20Topics%20Distributor.pdf

For the moment, let's assume that the nozzle was sized properly. :)