another old boiler

Good afternoon. Todays' question about the safety of an old boiler has prompted me to ask a similar related question. I have a boiler made for a County Carlow loco. which appears to be really nicely made, fully silver soldered except for the inner firebox which is unsoldered. The threaded stays are all nutted except for one up in the " belpair part" which is missing the nut and is extremely hard to get my large hand in to put a nut on. Like todays' other questioner my intention is to commission the boiler to use for running stationary engines. Two questions I suppose. How crucial is the missing nut if I was running the boiler at say 50psi ? Also I am assuming that comsol is my only option for caulking the stays. Any advice would be most welcome,

The original article on building County Carlow’s boiler says use ‘one of those high silver content solders’ over the stayheads outside and then over the nuts and thread ends inside with the same stuff.

IMHO this suggests the boiler is unfinished and that the missing nut is needed and then the inside stays need caulking with Comsol or similar.

ME Jan 2 1970

I've made extremely long nut runners to get into awkward places by loctiting a cap head screw into a pice of tube, or bar with a hole drilled up it.

You need ingenuity! A method I have used is to find a length of rubber tube that the nut fits tightly, and use it as a flexible drive to run the nut up the thread. This can work even if you have no access straight on. Getting it started may need something to reach in and guide it initially, perhaps wire with the end coiled to fit round loosely. If you can get the nut started and most of the way home, find a spanner, small ratchet or what have you to finish tightening from afar.

Edited By Macolm on 21/03/2023 17:46:21

Thanks chaps the rubber/plastic tube it is then.

Impossible to say without having access to the full constructional details and doing the calculations. (Or CAD modelling the boiler and letting the software do it.)

My reaction is an unstayed boiler is unsafe at any working pressure, don't risk it. Stays are specifically inserted to protect the structure at weak points and are therefore essential. That part of the boiler needs to be right. Fix it as the other answers describe.

There are many examples of full-size boiler explosions due to stay failures. Corrosion and other problems can be hard to see and metal fatigue is a non-obvious problem. Each time the boiler is steamed the unstayed section of boiler plate balloons slightly. The in-out cycles strain the metal that bit more every time until it comes apart, most likely at full pressure and with spectacular results.

Dave

Stays intended for soft solder caulking are usually screwed into the copper, so even without the nut it would not be 'unstayed'. However copper isn't all that strong, which is why a nut is usual, then you stop it leaking with solder, comsol preferred. I reckon it's a bit dodgy without. Chap in our club had a loco he'd inherited which had soft soldered stays. He managed to boil it dry, and the soft solder around the firebox stays melted. The firebox didn't collapse. By rigorously cleaning it up and resoldering he managed to resurrect it, but not an exercise to be repeated

Thanks again chaps, will definitely sort the nut issue before doing anything more.