Single pipe steam valve leaking : Brass Washer or ???

1890ish

This forum is amazing. I resolved some issues with help last year now running at really low (0-1) psi, but I still have an awkward valve leaking where it connects to the single steam copper pipe.

It's in a tight spot so I took the rad out  to get a closer look. I noticed that the copper steam pipe is flat at the end (not cone-shaped) where it goes into the brass radiator valve.

I want to get a better seal. I don't think pipe joint compound is the right tool for the job

I'm hoping to avoid cutting or sweating new pipes. I know doing that and using black steel would be better but this is what I'm working with.

Attached are three photos. 
1. Rad before disassembly

2. Pic of leaking joint covered in compound

3. Annotated disassembled rad and valve. Blue indicates how things fit. Red notes describe the problem.

What kind of washer or fitting can I use to stop this from leaking?

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Jamie Hall

Is there any taper to those threads? My first thought is that they might be more or less ordinary NPT threads. You can check by spinning the valve onto the fitting; it should go on easily at first and then get tighter but continue turning. If they are indeed NPT threads, the seal is in the threads -- not at the end -- and the solution is to get a few wraps -- maybe three or four -- of teflon pipe tape on the threads, and maybe some teflon dope, and see if you can tighten in up. Use two wrenches -- crescent or good fitting open end -- for this. One to hold the fitting attached to the copper pipe, and one to turn the valve. Turn the valve on by hand as far as you can, and then use the wrenches. Always finish up by tightening, not loosening, to get the valve stem at the angle you want it.

1890ish

Thanks Jaime. There's no taper on the copper pipe threads, but the valve does appear to be tapered... although I can easily thread the valve on all the way to the end. 
Maybe a new valve would do the trick?

mattmia2

A few layers of teflon tape and some dope or find some single strand ball wicking and wind a strand of the wicking in to the threads then use dope. It should be tapered.

Insulating the copper would help with some of the problems of copper not being suitable for steam.

reggi

Don't forget to clean the mating surfaces as that is a mess... what was on the threads ? The piece looks like it was really heated and the black looks like flux.... Are all your radiator connections done the same way ?

pecmsg

There was a taper!

Several layers of teflon tape and something like Block pipe dope on top. 

1890ish

reggi said:

Don't forget to clean the mating surfaces as that is a mess... what was on the threads ? The piece looks like it was really heated and the black looks like flux.... Are all your radiator connections done the same way ?

I only cleaned the leaky side in the last photo. I used a small steel bristle brush and a cotton rag. I'll clean up the other side too before piecing it back together.

To answer your question, it is the only connection done this way. It is in a part of the house that was added in 1997. Even the valve is strange - it is a straight valve with what seems like 1.25' fitting on the female side and 1.5" fitting on the male side.

I wonder whether I should get a new valve or try my chances with fresh dope and wick. I don't think I've ever had this connection apart so maybe careful ball-wicking + dope will work. I sealed the pipe with pipe dope and a steel cap instead of putting it all back together for now while I consider my options. Unlimited time/money I'd move the valve completely from this location to a better location in the basement where it's easier to reach but trying to keep the scope reasonable.

1890ish

pecmsg said:

There was a taper!

Several layers of teflon tape and something like Block pipe dope on top. 

Do you mean there's no longer enough of a taper? If so I have to get a new valve, right?

mattmia2

1890ish said:

pecmsg said:

There was a taper!

Several layers of teflon tape and something like Block pipe dope on top. 

Do you mean there's no longer enough of a taper? If so I have to get a new valve, right?

If taper was lost it would be in the male adapter on the copper. Brass isn't particularly malleable but copper is. look closely to make sure the valve isn't cracked.

1890ish

The valve isn't cracked as far as I can tell.

Do you mean the taper from the copper threads at the end of the copper pipe, in which case we'd take the fitting off and sweat a new fitting on right?

I used Hercules Pro Dope Gray Plumbers Sealer

Jamie Hall

I'm still curious, and I don't think we've found out. Is that an NPT thread on the copper to threaded pipe fitting? Is it an NPT thread on the valve? That would be the most common arrangement, although fittings do exist which are straight thread. They have to be handled very differently, as they aren't designed to seal on the threads, unlike NPT threads, which do.

1890ish

Ok, I'll try to clarify. My concern is fixing where the copper-pipe meets the brass-valve. This is where the leak is.

I can't tell if the male fitting on the copper pipe is tapered or not. I don't think it is. I wonder if I could use calipers to tell whether it's tapered?

I think the female brass end of the valve IS tapered. I can see/feel a taper. Oddly, I'm able to thread the copper fitting all the way to the end of the brass valve threads, with a hard stop when the copper threads reach the end of the brass threads.

ps. Technically, it's the brass valve being threaded onto the copper fitting, by spinning the brass valve.

Jamie Hall

Not being there, I'll trust your judgement -- and that means that someone gave you mismatcched fittings.
Somehow that adapter on the end of the copper pipe may not be NPT, but SAE. It shouldn't be possible to thread the two together -- the pitch is sllightly different (NPT is 11 and a half per inch, SAE is 12) in that size, but... If that is the case, however, you will need a properly sized o-ring at the bottom of the fitting (female thread on the valve) to get a seal. If both are SAE, which is possible -- fittings are made both ways -- you still need the o-ring. SAE threads are NOT intended to seal on the threads.

mattmia2

1890ish said:

I can't tell if the male fitting on the copper pipe is tapered or not. I don't think it is. I wonder if I could use calipers to tell whether it's tapered?

You can use calipers or a micrometer or put a straight edge on the threads and see if it is parallel to the pipe or if it tilts in.

I suspect it is npt but the tolerances of both it and the valve are off and maybe it has been deformed some the first time the valve was put on such that it bottoms before the threads bind up. If you put enough sealant in the threads like wicking or teflon tape it will still seal. Thee are lots of applications where straight thread bolts go in to water jackets or oil galleries and are sealed with thread sealant.

This is single strand wcking. it works better than teflon tape because it sits down in the valley of the thread and doesn't build up the overall diameter like teflon tape:
https://www.supplyhouse.com/Wal-rich-1906004-Spool-Wick

I asked if the valve was cracked because if it is split where the adapter threads in then it will expand at the split instead of tightening.

mattmia2

you can also measure a couple threads with a caliper or micrometer and calculate the pitch. if it is npt or nps it will be 14 threads per inch.

EBEBRATT-Ed

I would do as @MikeAmann suggested. You need a new adapter for sure and maybe a new valve. Someone stretched it out probably from over tightening. You can try sealing it up with a lot of teflon and dope but if you already have it all apart you might as well fix it right

pecmsg

Go to the hardware store and get a 3/4" Male Adaptor. Screw it into the brass valve, there should be 4 or 5 threads exposed hand tight. Use your wrenched and tighten. It should be very tight with 2 threads exposed.

No dope or Teflon, just dry fit!

Chris_L

I would try a lot of Teflon tape on the existing fitting first. Use the heaviest tape you can find, and if there are threads exposed after you tighten the valve, you might be ok.

If that doesn't work, I would use a new brass adaptor on the pipe--not copper. I've have problems with copper NPT fittings leaking on water pipes.