Understanding radiator valve sizing

[Stormflex]

I need to replace the valves on two radiators as they drip/leak badly when the radiator is removed and I need to leave the two rads off for a week whilst a decorator is in doing some work (and I'm on holiday). So, I decided the best thing was to replace them...

I went to my tame plumbers merchant and bought four Cosmos valves but guess what they don't fit - just my luck.

The 15mm compression nut to fit to the copper is fine. But, the inlet/outlet which attaches to the tail from the rad is not a match. I have looked on various websites but can see no mention of different sizes, other than the odd 15mm x 1/2 - but I'm not clear what this means, which measurement is 1/2?

In fact, the nut on the radiator is the same size as the nut on the 15mm compression.

And yes, I've tried removing the tails from the radiator to fit the new ones supplied with the valves but can't move them at all.

Any clarification would be much appreciated.

 

[corgiman]

1/2 is half inch or 15mm

your rad valves are probably 3/4 (three quarter inch) unions

ask your merchants for them

 

[ChrisR]

Hang on, room for confusionment here.
The holes in the rads will be 1/2 inch.
Older style rad valve unions had 3/4 inch unions in the middle.

So you either have to get the rad "tails" out, and use the whole thing (ignore different cap)

or buy valves with the older type central union.
I much prefer the older type cos you don't have to bend the pipe to get the rad out.

If you mix old and new, put something like LS-X sealer at the junction in case it isn't a perfect fit.

 

[Stormflex]

Chris,

Looking at your two images I need the latter of them where basically the two nuts are both the same size.

Can anyone recommend a plumbers merchant around Poole?

Thanks

Richard

 

[ChrisR]

Plumb Center do Bulldogs like that.

 

[Stormflex]

Nice one, thanks again

Richard