TXV's To Adjust or Not to Adjust - That is ....

[Refrigerologist]

philfridge, refrigerologist i apologise for the misquote - I don't know what happened... I just hit the quote button like I normally would, lots of the quotes in this thread appear to be messed up

Anyway i completely agree with US Iceman in regards to total suction superheat and mass flow rates, one of our customers - a large supermarket chain in aus specifies a maximum suction superheat (as do the comp mfg's) but fits stub probes and really likes to see around 10K at the stubs entering the suction header, which normally lands the evap superheat around the 4 to 6K mark, and yes this total superheat is affected by line sizing and insulation quality, and I guess through experience 10K provides a decent mass flow rate (when compared to say 20 - 30K). It can make setting stores up a little tedious when they are so perdantic (spelling?) about stub temps, it requires a little tweaking to keep them satisfied with both evap and total superheats but I guess it keeps us commissioners on our toes a bit.

No argument from me here! I just wish I hadn't started this thread, I knew it would be trouble

[NH3LVR]

If the fans are not runing and the valve closes, what difference does it make which orfice size is installed? Closed is closed. If the coil is flooding the valve should respond unless the piping arrangment and bulb location permit flow through the bottom of the suction pipe without cooling the bulb.
There will be little or no superheat to open the valve.

[US Iceman]

I just wish I hadn't started this thread, I knew it would be trouble

Call it a community service.

It might seem like you opened Pandoras box, but I don't think so. These are the types of discussions that once in print help to support learning for others.

The only down side in setting the TXV's to control the total superheat is that now the compressor bodies may sweat or have frost on them depnding on the application. Then someone thinks the compressor is flooding back and resets the TXV's so the compressors run HOT AGAIN!

[US Iceman]

If the fans are not runing and the valve closes, what difference does it make which orfice size is installed? Closed is closed. If the coil is flooding the valve should respond unless the piping arrangment and bulb location permit flow through the bottom of the suction pipe without cooling the bulb.
There will be little or no superheat to open the valve.

Or unless the power element lost it's charge. Then it could potenitally seep liquid since the valve is only responding to pressure changes alone (inlet and outlet).

[NH3LVR]

Or unless the power element lost it's charge. Then it could potenitally seep liquid since the valve is only responding to pressure changes alone (inlet and outlet).

I need to think about that awhile. The few cases I have seen the TX valve shut down when the head failed.

[US Iceman]

I need to think about that awhile. The few cases I have seen the TX valve shut down when the head failed.

This is a little bit of a stretch I know. But as you have stated already, if the fans shut down the TXV should close also.

This is the only way I can think of where the valve might tend to leak liquid sometimes (although I don't think it would not be a great amount by any means).