Rad tail query

[MickyP10]

Just removed a radiator which has a 50mm tail, but the internal diameter of the tail is quite small (I'd guess 8mm); ie not 15mm like the other end. Had a look at Homebase tails (only because it's the only place open) and they're the same. Can you not buy tails with a 15mm internal diameter? Seems a bit naff otherwise.

 

[dextrous]

I'm probably tired, but what radiator "tails" are you talking about?

 

[MickyP10]

Got a room extension and plumber bod teed into other rad on other side of wall, but new rad was a teensy bit narrower, so he fitted an adjustable radiator valve extension so pipes lined up either side of wall. Just removed rad (another story) and noticed the internal diameter of the tube is about 8mm and the valve has a much smaller internal hole than 'normal' 15mm rad valves (not the sleeve. That's 15mm, else it wouldn't fit...). Which set me thinking that it was like blocking your radiator up with a sock. I looked in at Homebase and the only 15mm adjustable radiator tails they stocked were exactly the same; ie tiny internal diameter. Wanted to know if this is normal, because it seems a bit silly if it is.

 

[petit_pablo]

Cant quite picture what you mean still but the majority of TRVs have a greatly reduced internal bore. Wont affect performance of system if its correctly balanced

 

[MickyP10]

Hi mate. Thanks for your reply. If you look inside a 15mm copper pipe or 'normal' 15mm rad tail, it has a 15mm internal diameter, as you would expect. The extension which came off my rad (and the ones which I saw at Homebase) have an internal 'tail' diameter of about 8mm, although they plumb in to 15mm systems. And I'm questioning whether this restriction on flow is damaging, causes turbulence, restricts flow to other rads, etc. I'm guessing, too, that I could buy a non adjustable tail which would have a 15mm internal diameter. But I don't know that, or where to get it.

 

[imroberts]

Do you mean something like this, which allows the fitting to slide about in case the radiator doesn't quite match up with the piping?

http://www.screwfix.com/sfd/i/cat/09/p1052609_x.jpg

Most of these have a fairly reduced internal bore. As someone has said above though, most TRVs have reduced internal bores anyway so you shouldn't see any loss of performance.

 

[tamz]

Probably used the adjustable extension tails which have a 10mm hex inside.

As long as the rad is under about 3kw it will not make any difference. As said before look at the inside of a trv, 8mm hole? Never had any incling to measure it

Btw, tails don't have a 15mm internal dia. 15 is the external dia. Don't worry about it.