I've been adding a couple of radiators, and have found that the radiator
circuit is 15mm (1/2") right from the boiler, so I'd like to increase to
22mm, but.....

The flow side appears easy, a special coupler appears to have been used on
the diverter valve, so I guess it will be easy to get a 22mm fitting, but
what sort of fitting wouild it be? it looks like a compression fitting, but
the present 15mm pipe lookks as though it has a flange on it.

Harder is the return to the tank, which I think is 1 1/8 inch, it has a
circumference of 3 1/2", and this has been reduced to perhaps 22mm
(circumference 73 mm) to go into my fairly recent back boiler.

But the way it gets into the tank beats me.

There's a sort of brass T, with the 1 1/8 pipe sweated into one side, the
other side has a female thread with a flange, with a piece screwed in with
string round the threads, and the other side of this is a 15mm compression
fitting that accepts the radiator circuit return.

In the top of this item is a fairly massive tee with one side going into a
stub of pipe which comes out of the actual tank fitting which appears to be
1 1/8, and the top has a deliberate 1/2" compression fitting with a
pressure relief valve on it.

I'm not too clear how it connects to the first fitting, there appears to be
a big flanged nut like a compression fitting, but they appear to have been
made for each other.
This all started life as a coal fired back boiler system.

Questions -

I am nervous of attacking the tank, but I have to, to end up with a 22mm
stub of pipe, then I can chuck the rest away with a couple of 22mm tees

Can I get a tank fitting that will do this - its a cylinder about 16"
across and 3ft6" tall?

Anyone know what the other wierd T type fitting is?

Very grateful for any help, I guess really I could fit a new tank, but I'm
not going to do that this year, but I would like to use 22mm for my main
rad circuit and branch off with reducing T's

Whew

mike r