Radiator valve union leak

arbalest

I've searched here and read several posts and I have tried everything and then some...

The valve joint was fine for years and now it's leaking from the back of the union nut. It is not the bonnet nut (which is fine).

I've had the union apart and together several times today. I've carefully shimmed everything so that the I can push the radiator into the valve and the union slides in to a full even seating. The seating is so even that I can turn the union nut by hand for several rotations before needing a wrench. I've visually inspected both seating faces and find no crud or notches. I tried telfon tape on the threads even though I know that should not matter.

I took the spud out and inspected it. No problem noted. Reninstalled with Teflon tape -- no leaks on that side.

Lastly, I tried some Teflon tape on the male seating surface and that makes things worse, rather than better.

It always seems that Murphy is working over-time at my place. Any ideas or suggestions would be appreciated.

update: This is a cast iron radiator.

Gsmith

Some have suggested putting a little dishwashing detergent on the male mating face of the union (a LITTLE).

Fred

You took the spud out and inspected it? Is it a new spud that you installed? If so, did you also replace the valve? Those spuds and valves are a matched set and a new spud isn't going to work with an old valve. They aren't machined like they were 50 or more years ago. If it's the original spud/valve or a new spud/valve, try rocking the radiator a little as you tighten the nut. Sometimes that helps seat the mating surfaces.

j a_2

Take a bright lite with your magnifying glasses and see if the nut is not cracked....

Jamie Hall

If it's not a matching spud and valve -- particularly if there is a significant age difference -- you're probably out of luck. If you replaced the original spud, though, you may be able to get it to stop leaking.

If the tightening gently while rocking slightly trick doesn't work...

First, take it apart again. Clean the faces of the union, both male and female very carefully with something soft. Be careful not to scratch them. Make sure they are really clean and smooth. They don't have to be shiny bright, but they do have to be clean.

Second, inspect them carefully. If there are scratches, you're done. You need a new valve and its matching spud. Otherwise...

Third, inspect the union nut. If it's cracked, you may have a problem, but maybe not. A union doesn't need a whole lot of torque on the nut, and the nut doesn't seal anything.

Fourth, now that you've gotten this far, bring the union together. Make sure it is aligned, both laterally (up and down and sideways) and angularly. Shim the radiator if need be.

Fifth, spin the union nut on by hand and tighten, gently, while rocking the radiator slightly. Do not use tape or pipe dope or anything else.

arbalest

Thanks all.

As far as I know the spud/valve are a matched set. They were both replaced 3-5 years ago and have worked fine until this winter.

I ran a utility knife around the mating surfaces to make sure there was no gunk that I was missing. So there are probably scratches now, if there weren't before. It sounds like light sanding the surfaces to clean them is not a good idea either.

I will get a new valve/spud set. And I will check the old nut with a light and a magnifier too just for the heck of it.

I have already shimmed things so that when I push them together they fit like a space ship docking to the space station - easy peasy.

I have not tried rocking and tightening at the same time because of the fit, but I will do that with the new valve/spud. But like I said in the OP, the alignment allows me several full turns by hand.

Might be worth asking - given that over tightening will break the nut, how tight should one wrench it after it is hand-tight?

Thanks again for all of the quick replies.

Jamie Hall

arbalest said:

Thanks all.

...
Might be worth asking - given that over tightening will break the nut, how tight should one wrench it after it is hand-tight?

...

Just enough so that when you rock the radiator gently, the spud and valve move as a unit. Half a turn, if that. Keep in mind that the union nut can't be used to pull things together!

HomerJSmith

With perfectly clean mating surfaces, clean with lacquer thinner, then try a product like 'lock tite', 'lockin seal on the mating surface. Give it an hour to cure.

I have had a lot of success with this product on difficult sealing applications.

MilanD

Go to 3:08 mark.
https://youtu.be/jHeCP21ik7w

MilanD

Or use blue block - see 13:36
https://youtu.be/-yGRgv2flfs

arbalest

Put in a new valve/spud and it's okay now. I still don't see a problem with the old stuff - not with the mating surfaces or the nut. Shrug.

nicholas bonham-carter

Any union will move a little bit, (1/10000 inch), with expansion, and contraction, and a clean lubricated surface will adapt to this minute movement better than one which has been buttered up.—NBC

New England SteamWorks

Replacing the whole valve was the correct decision. Bravo.