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Copper pipe Diameter Reduction

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Brian Meek28/03/2020 17:49:40
3 forum posts

Repairing my central heating system, I have difficulty in mating modern 22mm o/d pipe with old ¾ inch bore system to fit a new pump.

The o/d of ¾ inch pipe is approx 21.3 mm, ie the metric bore of two valves. I have solder‑in adapter sleeves, ie 22mm to 21.3mm, but their length plus a length of ¾ inch pipe each is too long to fit into place.

A You-Tube video showed a very old tool to squeeze 22mm down to 21.3 mm, but no comment on its effectiveness. Is this feasible or safe?

Perhaps I could make one.
I would have thought that a rolling system would be necessary.

Any advice would be very welcome.

JasonB28/03/2020 20:04:44
17850 forum posts
1954 photos
1 articles

Use pump valves with 22mm compression but change the supplied olives to 3/4" olives which will fit your old pipework..

Steviegtr28/03/2020 20:24:38
1163 forum posts
99 photos

They sell a sleeve. That fit over the 22mm & slides down ,it has no centre crimp. I had to use one when I fit the new boiler. You can then make up you fittings & then line up & slide the socket over the centre of the joint to solder. Hope that makes sense.


Former Member28/03/2020 20:30:52

[This posting has been removed]

Brian Meek29/03/2020 14:47:00
3 forum posts

Thank you for your replies.

As stated I have tried reducing-sleeves.
Their external length does not leave enough room free for the nut to compress the olive.

Room is tight because I cannot move the mating valve.
It is close to a right-angle bend that I need to connect (it is 22mm bore).

Hence my need to have a reduced diameter over a short length.

Hope this makes sense.

frown Brian

Former Member29/03/2020 14:59:26

[This posting has been removed]

noel shelley29/03/2020 15:12:57
90 forum posts

For reducing pipe diameters I use my hydraulic pipe swaging press. With 8 dies it gives a near perfect circle. To increase a copper pipe size machine up a tapered(3/4"of I/D size,taper to new I/Dsize, 1" of new I/D) dolly,lubricate and drive down the pipe. This works best on thicker walled pipe, modern due to copper costs is often to thin even to bend properly without kinking. If your near by I may be able to help. Best wishes Noel.

Norfolk Boy29/03/2020 22:37:03
48 forum posts
14 photos

There is also a compression coupling

blowlamp30/03/2020 00:00:11
1308 forum posts
83 photos

You might be able to use an ER collet to swage some 22mm pipe.

What about turning/drilling some brass bar to the right size to make a suitable fitting?


Bazyle30/03/2020 01:16:01
5139 forum posts
199 photos

How about the device used for cutting copper pipe that looks like a gclamp to screw down a cutting wheel onto the pipe. Replace all wheels with rounded wheels that can be progressively squeezed down onto the well annealed pipe while rotating.

Alan Charleston30/03/2020 06:37:00
83 forum posts
20 photos


I made a tool which bells out the ID of 1/2" copper pipe to the OD so two pieces can be brazed together. The small diameter is 1/2" followed by a slow taper till the OD is reached then a parallel length at the OD. The pipe is grasped in the left hand and the 1/2" section is inserted. The tool is then whacked with a big hammer until the desired result is achieved. It probably wouldn't hurt to anneal the copper first, although I haven't had any pipes crack.

Obviously the dimensions would be changed to suit your pipes.

Michael Gilligan30/03/2020 07:30:43
15478 forum posts
668 photos
Posted by Bill Chugg on 28/03/2020 20:30:52:

A SLIP COUPLER is the technical name, so my plumber son has just informed me.



There was some discussion of those on this recent thread: **LINK**


Speedy Builder530/03/2020 08:07:07
1985 forum posts
139 photos

make a brass solder nipple to fit the 3/4" pipe but with "olive" dimensions for the 22mm fitting

oops,  the cut and paste photo didn't work - look up "Solder pipe nipple". on google


Edited By Speedy Builder5 on 30/03/2020 08:08:54

Brian Meek31/03/2020 20:05:11
3 forum posts

Many thanks to all of you who answered my query.

Nothing to photograph as system is dismantled.
Just need to reduce the O/D of 22mm copper pipe to approx 21.3mm, preferably without sleeves.

Seems I must think again.

frown Brian

Grizzly bear31/03/2020 20:25:44
232 forum posts
8 photos


There has been numerous good suggestions, why can't you use any of them?


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