Hollow stay

[JonL]

I'm about to put the hollow stay in my Britannia boiler and to be honest I'm a bit confused. I've spent a while trying to see where the thread starts (i.e. 6 o'clock on the fitting) at both sides and its very hard on the smokebox end. 

I've been told that I shouldn't worry about it and they will just line up. Keith Appleton on one of his videos says "I don't know how it works but it always does...."

How does this happen? Is the pitch of the thread fine enough that the slack each end takes into account a certain amount of misalignment? As with all boiler fittings I'm very cautious of damaging threads.

Does anyone have any good tips? Or do I just solder a threaded union on each end and just whack it in? 

Sincerely, Nervous of North Dorset.

[jo479]

I've always done it as LBSC described, put your threaded stay through the Backhead, through the bush in the smokebox tubeplate, fit the threaded bush over the stay then wind the bush into the smokebox tubeplate, then fit your blower valve (normally 3/8" 40) into the backhead, never had any problems, it's easier to do it than describe it.

[uuu]

The boiler plates are not completely rigid, particularly when in the annealed state before they've been stressed by the first pressure test. So you'd be able to move them with quite gentle pressure. Half a thread pitch overall - a quarter at each end - would not take much effort at all.


Wilf

[JonL]

Ok that makes sense. I think the thread is 32 TPI in this case, so less than a milimeter flex required. As the backhead is sloping it may be less flexible than the other end...

I'll have a go and just be very gentle, last thing I need is a nadgered thread.

Thanks to you both.