Choosing the correct TXV

[dave1234]

In the hopes of being a better tech I was hoping to get a better understanding (since you all have great ways of explaining things) of how to choose TXVs for a giving system. I understand evap and spring pressures close the valve and the bulb opens it but what is considered when choosing a balanced port vs external equalized vs internal equalized ect and the applications in which one is better than the other. How can you tell the differance just by looking at it- obviously the equalizer line means its externaly equalized. Also what and when is a cross-charged bulb used vs ... ... brain fart, what do you call the type with like gas charged bulb again? Also I'm hoping to put a controversy to rest- is the bulb position REALLY critical on less then 3/4" suction or not :couchhide:

[dave1234]

I shouldv'e read the nearby thread about plugged equalizers first lots of good stuff there. But still questions remain.

[crymtide]

Mounted horizontally, bulb position is always critical 4 or 8 o'clock. then you have no chance of reading the oil instead of the refrigerant. Vertically doesn't matter as long as the captube is on the bottom. The best method is to develope a method and always stick with it. if it works don't deviate. The TXV is chosen according to evap size, and the simple way is to take the Model and S/N to the supply house and let them look it up as to size, and give you the right one.

[icemeister]

In the hopes of being a better tech I was hoping to get a better understanding (since you all have great ways of explaining things) of how to choose TXVs for a giving system. I understand evap and spring pressures close the valve and the bulb opens it but what is considered when choosing a balanced port vs external equalized vs internal equalized ect and the applications in which one is better than the other. How can you tell the differance just by looking at it- obviously the equalizer line means its externaly equalized. Also what and when is a cross-charged bulb used vs ... ... brain fart, what do you call the type with like gas charged bulb again? Also I'm hoping to put a controversy to rest- is the bulb position REALLY critical on less then 3/4" suction or not :couchhide:

Most, if not all, of your questions will be answered in Sporlan's Bulletin 10-9 (http://www.sporlanonline.com/10-9.pdf).

You mention balanced port valves. For most applications, the standard valve is perfectly acceptable. The balanced port is designed to give better superheat control over a wider range of conditions and capacity that the standard valve and is often used in supermarket work where such things as floating head pressure, natural subcooling and mechanical subcooling are used.

Is one better than the other? Sure, the balanced port wins because it can do anything the standard valve does, only better.

The internally vs externally equalized valve question depends upon what type of evaporator you have. If the evaporator has no distributor and has a very low pressure drop <2 psi, then the internally equalized valve is fine. If it has a pressure drop type distributor or has a pressure drop > 2 psi then an externally equalized valve must be used.

Generally speaking, in the field, if the evap coil has an equalizer tube, use the externally equalized valve. If it doesn't have an equalizer tube and all you have is an externally equalized valve in the truck, just add an equalizer tube. That will work every time. When in doubt, use the externally equalized valve.

As for the thermostatic charges, keep it simple. All you need to remember is VGA for A/C, C for medium temp, Z for low temp and ZP for low temp where the pressure limiting, compressor overload protection of an MOP type element is needed. (I'm using Sporlan nomenclature here BTW.)

The orientation of the sensing bulb is always 4 or 8 o'clock for me. ;)

[Andy Schoen]

Vertically doesn't matter as long as the captube is on the bottom.

Vertically may require some experimentation to obtain best control. It makes no matter if the cap tube is on the top or bottom. Old wives' tale. Actually, I've been advised that some long retired Carrier engineer(s) thought the cap tube should be oriented on the top if the thermostatic charge was of a liquid or cross liquid type due to a "pumping" effect from static head due to the charge. The math, however, indicates bulb orientation would have little effect on static head.

[Joe Harper]

This was all confusing for me when I started this line of work. What helped me the most was sitting down with the catalog (not sales phamplet) and reading about each valve and the charts and the differences with each one.

As far as balanced port goes, that is most common type that I install. The outdoor temps here range from mid thirties to 125 (on rooftop mounted units). It keeps the superheat pretty even over the wide range of temps. Also, externally eq valves usually go on multi-circuit evaps, while internally will go with single circuit-where the suction and liquid line do not branch out into smaller runs (if someone has a better way to explain that please let me know).

And whatever Andy tells you is not to be questioned...:patriot:

[mud]

The TXV is chosen according to evap size, and the simple way is to take the Model and S/N to the supply house and let them look it up as to size, and give you the right one.

Yeah but it's always nice to be able to figure out if they gave you the wrong one.

[Phase Loss]

Around in my area a good rule of thumb is to NEVER trust the counter guy...there is a reason he is behind that counter.

I'm sure there are good ones out there, just not in my area :)