Fitting TRVs

Is the connection between a radiator tail and the actual valve any sort of standard? And/or the overall "width" of the valve?
I'm trying to work out what my chances are of swapping the existing valves for TRVs without fitting new tails and adjusting the pipework.
Since it's cold, I want, for a change, to estimate the duration of the work before I start it.
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On Friday, November 8, 2019 at 10:12:17 AM UTC, snipped-for-privacy@blaukopf.com wrote:

This bit is a stupid question isn't it. It must be either 3/4 or 1/2" because why would anyone bother setting up for anything else.
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On Fri, 8 Nov 2019 02:16:35 -0800 (PST), snipped-for-privacy@blaukopf.com wrote:

I think you have missed the point of the question by snipping and only replying to one bit (missing the 'bigger picture' in the process).
It wasn't the diameter of the input pipe, it was the distance between that pipe and the radiator, something someone replacing a std with a complete new TRV would like to know.
Cheers, T i m
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On Friday, November 8, 2019 at 11:12:09 AM UTC, T i m wrote:

Not quite, because I replied to my own question!

I was referring to the size of thread that connects the valve to the tail, and realised that surely no one would make it anything other than 3/4 or 1/2, so if it looks like a 1/2, it is a 1/2.
it was the distance between

That question stands.
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On Fri, 8 Nov 2019 03:18:08 -0800 (PST), snipped-for-privacy@blaukopf.com wrote:

Doh! ;-)

Well, I'm not sure you can even assume they will be interchangeable, even if they are nominally the same size / type of fitting.
I say that because I have gone to replace say a gate valve and hoped to retain the existing nuts / olives, only to find the thread a different pitch / tightness?

I think has been answered elsewhere. I think with my experience with plumbing, unless you are replacing exact like for like, there is a good chance that something will be different (and rarely in your favour). ;-(
Cheers, T i m
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On 08/11/2019 11:40, T i m wrote:

I have certainly found in the past that things were not interchangeable - even nuts from one compression fitting to another - but everything I have used in recent years has been (replacing gate valves with lever ball valves, straight couplers with isolation valves and the like). Maybe manufacturers used their own standards in the past, but these days do stick to standard lengths and threads?
SteveW
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There used to be at least two different threads on compression nuts for domestic size pipes, but in recent years they all seem to be BSP, I would really expect any domestic radiator valves in the last 15 years or so to be directly interchangeable. ICB, and when I was in a hurry probably would be.
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Roger Hayter

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On 09/11/2019 01:05, Roger Hayter wrote:

Last year I had to replace a 3 port (CH) valve where the old one was less than 10 years old. The threads didn't match.
At first it did appear to tighten up but I had a small weeping leak. Comparing the old and new treads they appeared to be the same pitch but a slightly different angle. After draining down for a second time and removing the old nut I tried it on the new fitting. It tuned a few times but then just started to bind up on the new fitting.
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You've rather obviously never done this job. The centres of the pipe and rad can be different between a LSV and TRV, as can the length of the pipe. Even the type of olive used different.
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*I have never hated a man enough to give his diamonds back.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Friday, 8 November 2019 11:33:41 UTC, Dave Plowman (News) wrote:

As noted elsewhere, I asked the question.

Damn. I have actually done it before (and had to change the tails), but everything looked a bit more standard this time. If I have to change everything I guess I'll give it all a flush too.
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On Friday, 8 November 2019 10:16:38 UTC, snipped-for-privacy@blaukopf.com wrote:

Before anyone else jumps in - I retract my assertion that the question (which I asked) is stupid.
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On 08/11/2019 10:16, snipped-for-privacy@blaukopf.com wrote:

Well its not as daft as it sounds...
The tail socket into the rad is almost always 1/2" BSP female. However the other end of the tail varies. Traditionally it was a cone fitting retained by a 3/4" BSP nut that was captive on the tail. However more commonly these days the tail is often just a length of 15 mm pipe, and the valve has a 15mm compression fitting that then connects to that (ultimately leaving a 1/2" BSP not captive on the tail, but retained by the olive rather than the cone fitting).
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John.
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My original TRVs, shed own brand, had an 'olive' which fitted to the end of the copper pipe, rather than the usual types which fits over it. And when replacement time came, couldn't find the same design.
But I'd only buy Drayton now. Saving a few pennies isn't worth it in the long run.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 08/11/2019 12:47, John Rumm wrote:

Definitely do not assume standard threads, you may have to remove the fitting that goes into the radiator, rather than just swapping the "valve" bit. This needs a big allen key and they are sometimes very tight from corrosion. In my experience you can usually get away with the slightly different dimensions by using the flexibility of the copper pipes, provided they are not too constrained close to the radiator. One of those jobs that usually takes longer than expected, IME.
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On 08/11/2019 17:02, newshound wrote:

Some of the modern ones seem to use a couple of flats on the stem to allow them to be turned with a spanner, rather than having the hex inner profile... Personally I prefer the hex versions.

Yup, although sometimes you get lucky...
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On 08/11/2019 18:10, John Rumm wrote:

The original rads in my 1976-built house have 3/4 inch female BSP socket, and the valves were fitted by a Gorilla using boss white and hemp.
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Not all makes of TRVs are the same or indeed interchangeable. So you need to look for ones which are a direct replacement.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 08/11/2019 10:12, snipped-for-privacy@blaukopf.com wrote:

You may get away with it if the physical size of the valves (inlet to outlet) match.
When I replace all my 20 year old TRV I had to change the tails in the radiator. The valve body on the old TRV was longer. In addition I found the screw thread on the compression nut on the old fitting did not match that on the new fitting necessitating removing the olive in order to fit the new nut. On many pipes removing the old olive was difficult and I found it easier to cut the old pipe and solder in a new piece. The exercise was complicated by the pipes having been painted and having to syphon any water out of the existing pipe(s) before soldering.
For the tails I already had https://www.screwfix.com/p/rothenberger-uni-spanner/95088 which made this part of the job much easier.
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On Friday, 8 November 2019 12:02:37 UTC, alan_m wrote:

That tool looks like a vast improvement on the radiator spanner I used last time. I used a radiator spanner and ended up having to hit it with a hammer to get it to shift.
As I was living in a flat, and doing the work in evenings, I did that particular job on bonfire night to minimise disturbance to everyone else.
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On 08/11/2019 12:07, snipped-for-privacy@airsource.co.uk wrote:

The ratchet handle is the same as you get with a 1/2 inch socket set for a car etc. so if you already have this maybe the stepped socket can be purchased separately. I don't know if the Screwfix is the same as mine as the one I have also has deep grooves in two faces of the hex steps to suite the fittings that have two internal lugs. This is shown in
https://www.ebay.co.uk/itm/Todays-Tools-Slotted-Radiator-Valve-Key-with-Ratchet-22mm-Socket-99-851/293188995826?hash=item44436d0af2:g:OKEAAOSwItRdVSlv
or
https://tinyurl.com/y64h5tk4
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