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Discuss Radiator Valve Threads in the Plumbing Jobs | The Job-board area at PlumbersForums.net

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Hi All,

Not a plumber but pretty handy with tools and experienced DIYer, however have come across a 'good one' that I am struggling with and wondered if someone would be able to provide some help.

I have a 1930's house and a set of radiators with what seem to be very odd tails on them. I need to remove the rads to decorate and the valve are leaking (1st problem) which means I need to replace them with a compatible thread patterned thermostatic valve (2nd problem)

I have been to a few plumbing centers and everyone I have spoken to says radiator tails are only one of two sized 1/2" or 3/4" so they have sold me the cap end nuts to stop the leaking while decorating, so I can replace the valves when I find the correct size.

I have taken a few measurements and can uploads some pictures if needs be.

Thread width = 21.5mm
Thread spacing (peak to peak) = 1mm
Parallel Thread

If anyone could help me with what this may be it would be greatly appreciated!
 
Post some pics of the valves please
 
excuse the mess on the walls, the rad seemed empty, then it wasn't!
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1/2 into the rad 15mm copper
 
Which bit are you trying to put the 1/2” into? Both connectors on the valve are 15mm the hole in the rad where the tail goes in is 1/2”.
 
So I am trying the cap the valve off because it is leaking, the valve has the male thread sizes as mentioned above the rad tail has the female 'nut' I am trying to put the 1/2" cap / end stop on the valves male thread.

Hopefully you can understand what I mean.
 
You won't be able to cap the valve off as it's old thread

But remove the tail from the rad and put the cap end on the threaded end
 
So you are saying the radiator tail thread into the rad should be 1/2"?

Would new radiator tails be 1/2 thus enabling me to replace tails with new ones and matching threaded thermostatic valves?
 
Correct if the trv is new eg last 10 years it should fit

The one in the pic isn't a trv it's a lock shield valve
 
Sorry for the confusing post about. Just read it back and that isn’t what I wanted to put but as normal I got distracted. Sorry.
 
thanks for the input, so to summarize, the lock sheild valves have an old thread that obviously matched the rad tails. but the rad tail thread should be 1/2"? if the outer thread is an old thread why would the thread that goes into the rad not be something other than 1/2"?
But if it is indeed 1/2" I can buy new tails for the rads with 1/2" BSP connections which will fit a new TRV with a 15mm to 1/2" connection?
 
The thread in the radiator WILL be 1/2" bsp and will take any 1/2"current valve tail.
If you want to cap the valve, loosen the tail and use the cap on the radiator end of the tail.

The thread on the valve compression nut(s) at 1mm pitch would appear to be manufacturer specific as Bsp 1/2" is approx 1.8 mm pitch.
1/2" compression nuts are almost always 1/2" bsp.
The thread on the nut on the pipe into / out of the valve will also be most likely to be non standard so you'll have to remove the nut and olive and use the ones supplied with the new valve. (this wood be good practice anyway)
 
I would just about put my house on it that the thread size on the valve to connect the tail would be 3/4" BSP.
If you undo the large nut between the valve and the radistor - that thread should be 3/4" BSP
 
But if it is indeed 1/2" I can buy new tails for the rads with 1/2" BSP connections which will fit a new TRV with a 15mm to 1/2" connection?
Yes, but it doesn't have to be a TRV. For the cost of an iso valve you could use one of them while you're doing the work. Probably use it somewhere anyway.
To answer your points about thread types - modern 15mm compression fittings use 1/2"BSP threads, but I have some old ones with finer thread. Obviously if you have both parts it doesn't matter. I also have 22mm compression fittings with different threads. Neither is 3/4"BSP as there is insufficient wall thickness for a 3/4"BSP thread when 22mm is subtracted from the OD of a 3/4"NB pipe.
will give getting the tails out a go at the weekend and see how it goes, fingers crossed!
They could be tight! Might be sealed with hemp and Bosswhite, which goes hard. Be prepared to warm it up with a blowtorch to soften it. If you give it too much welly you might rip a piece out of the rad.
 
That is an old Peglers Terrier rad valve and if the thread is very fine, then it is the older type thread Peglers used, of 1970s era.
You can’t be experienced in plumbing if you can’t plug the radiator or the valve?
Just push the nut and olive from the old tail by using an adjustable spanner with a twist behind the nut. Then you can fit a brass stopend on old tail, if you really must.
Or the old nut can be used with a new olive and a cutting of copper that has a stopend on other end, to provide a seal off pipe.
 
That is an old Peglers Terrier rad valve and if the thread is very fine, then it is the older type thread Peglers used, of 1970s era.
You can’t be experienced in plumbing if you can’t plug the radiator or the valve?
Just push the nut and olive from the old tail by using an adjustable spanner with a twist behind the nut. Then you can fit a brass stopend on old tail, if you really must.
Or the old nut can be used with a new olive and a cutting of copper that has a stopend on other end, to provide a seal off pipe.
Old pegler valves use bspf threads not standard BSP as do all valves now.
 
Old pegler valves use bspf threads not standard BSP as do all valves now.
That's interesting. I've not heard of coarse and fine BSP threads. Can you give more detail? I looked on Google which didn't say anything. As I said in #17, for eg 22mm, compression fittings aren't 3/4BSP, and the modern coarser thread is finer than 3/4BSP.
 
That's interesting. I've not heard of coarse and fine BSP threads. Can you give more detail? I looked on Google which didn't say anything. As I said in #17, for eg 22mm, compression fittings aren't 3/4BSP, and the modern coarser thread is finer than 3/4BSP.
This has gone a bit quiet.
All my rad iso valves are old, about 30 years, and the the valve tails are 1/2BSP (of course), and the tail has an internal 13mm drive hexagon. The valve has 15mm (or maybe 1/2") compression on the pipework side.
The valve rad side has a male thread, with same OD as 3/4BSP, but finer thread. A 3/4BSPF fitting goes on about 1 turn. Estimated 19 TPI (same as 3/8BSP), vs 14 TPI for 3/4BSP. Anybody know what thread this is? I've never heard of a fine series BSP, and I can't find anything on the internet.
My TRVs, and I believe modern iso valves, have 15mm compression both sides, and the rad tail has external spanner flats.
 
This has gone a bit quiet.
All my rad iso valves are old, about 30 years, and the the valve tails are 1/2BSP (of course), and the tail has an internal 13mm drive hexagon. The valve has 15mm (or maybe 1/2") compression on the pipework side.
The valve rad side has a male thread, with same OD as 3/4BSP, but finer thread. A 3/4BSPF fitting goes on about 1 turn. Estimated 19 TPI (same as 3/8BSP), vs 14 TPI for 3/4BSP. Anybody know what thread this is? I've never heard of a fine series BSP, and I can't find anything on the internet.
My TRVs, and I believe modern iso valves, have 15mm compression both sides, and the rad tail has external spanner flats.

Are you talking about the old large nut tails which have tapered flange on tail and valve? You can still get quality valves like that, but Trvs are now rare with that tail.
Why worry about them? Just remove the tails and install the new valves and tails
 
Are you talking about the old large nut tails which have tapered flange on tail and valve?
Probably, if what you mean has same diameter (but not TPI) as a 3/4BSP.
You can still get quality valves like that, but Trvs are now rare with that tail.
Interesting that they're still available and considered good quality. As I said, my TRVs are 15mm compression both sides.
Why worry about them? Just remove the tails and install the new valves and tails
I'm not tackling a job at present, just curious. But thinking about it a bit more, I don't know what the thread is on 15 compression (earlier ones which aren't 1/2BSP), or 22mm compression (at least 2 different TPIs, neither 3/4BSP). I'd have expected makers to use a standard thread of some sort, but maybe not, and they do a special. Obviously as you have both parts it doesn't matter.
 
Will be same threads as Honeywell zone valves or kuterlite compression fittings being BSP parallel threads.
 
most imported compression fittings are standard BSP kuterlite is not also zone vale manufacturers have for many years bastardised their threads for some reason, maybe their supplier. I have not read all the posts but 15mm has been 1/2" bsp 14 TPI for over 40 years but there is some stuff out there older. We do refrigeration work also and come across all sizes of pipe thread, BSP, BSPT, NPT and on the odd occasion APT they are not that much different but they are different
 
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