Hi , I have a Reynolds DV3K wheelset on it's way, with a 46mm rim height. Will 52mm valve stem work on these wheels (i already have them in ultra light) ?? And what would be the ideal stem length be ????

No.

I find I have to add an extension to normal length tubes on 40-50mm rims. The only standard off the shelf tube that I am able to get to work well are 80mm...but they'd be a tad long on a 45.

Keep in mind 25.4mm = 1 inch. 1 inch is barely enough to have a pump work well - depending on the pump.

I have Reynolds Assaults (46mm deep) and the 51mm valve on Vittoria latex tubes is just barely long enough. Sometimes I have trouble pumping up the front tube (the stem seems to be slightly shorter) and can get around it by turning the presta valve back in by 1 or 2 turns.

When I got the tires, I got 60mm Bontrager tubes and was bummed to not be able to use the latex tubes. One day, I had them apart and tried it and was pleasantly surprised that it worked.

YMMV

Bob

So an extension should work on a 52mm stem in a 46mm rim ???
I don't care about the looks of a 80mm stem in a 46mm rim but is there any other reason I wouldn't want to use a 80mm ??? If I go with a 60mm I still need to carry a extension. unless my spares are 80mm.
The extension doesn't stay on the wheel after it's aired up right ?? never used them

So If I was to order new tubes I would be ok with 60mm **********

For my 50mm, I ran 48mm valves and a 33mm SRAM extender.

60 may or may not work depending on what kind of pump you use.

I use 60mm stems with my DV3K's. I Use lezyne pumps where the part at the end of the hose screws onto the valve. I can see how some pumps may needs more of the valve stem exposed.

OK , I sound like a noob, does the extender stay on the original stem after tube has been aired up ????

I just broke my valve core seeing how much my pump goes down the stem.. My second one this week. They should be replaceable . Is that an option ??? Now I have a use for my 52mm tubes (training wheels)

You unscrew the valve head completely, wrap some teflon tape on the threads of the valve, screw on the extender, inflate...

https://www.youtube.com/watch?v=S9YLlZDIOkU

There are two types of valve extenders. One is designed for use with removable valve cores and the other is designed for use when the valve core is not removable. If you valves stick out just a bit (i.e. not long enough to get the pump head on but long enough to open and close the valve), then it would be perfectly reasonable to use a short valve extension only while pumping. This would have the advantage that you can close the valve stem so it won't rattle or lose air while you are riding. People with deeper wheels, where the junction between valve and extender is within the rim, don't really have this possibility.

Of course you probably should carry the extension with you for use with your spare(s) or have longer valves on your spares.