Given the situation, I’d be tempted to drill out the stumps of the studs down to the level of the soldered-in bush. The gland housing might then be persuaded to rotate and allow unscrewing of the complete regulator, assuming that it is more or less to drawing. For reassembly, the gland housing could be re-drilled and tapped between the existing stud positions. The gasket will take up the micro difference.

The drawing shows 7ba studs, but they look bigger on the photos. Even so, if the 2 broken studs are diametrically opposite and you drill them down level as suggested above, 4 off 7 ba studs would be sufficient to hold the regulator assembly provided the threads are in decent condition.

Assuming 80 psi, the force applied by steam pressure is 23 lb, 4 off 7 ba studs have a core area 0.0177 sqin, so stress is ~1300 psi. In reality, a lot of the force is resisted by the assembly being screwed into the front tube plate.

Let’s be honest it’s a pretty rubbish design. I know it works, and lots have been made, but it’s asking for problems when you come to maintain it.

GUYS, look at the drawings that Nick provided!  The whole assembly from the smokebox end to the backhead needs to be removed as the regulator is on the smokebox side of the dome.  Spinning off the regulator boss on the backhead will not achieve what the builder wants to do viz: “Free off the regulator”.

Even removing the superheater bush may present problems, as the threaded internal tubes may unscrew from either side of the internals of the regulator. lets hope some of the screwed joints were soldered during assembly.

My take on it is remove the super heater bush on the smokebox plate and the whole regulator could be pulled out from the backhead end. (Notice the word “could” as nothing is certain!!

Bob

I had this same problem with a William I bought part built. I ended up gently sawing off the edge of the flange containing the broken stud (allowing me to get some grips on it to spin the stud out), once they were out I could turn the regulator tube and then remake the rear flange. When I put it together, despite what some of the advice in this thread says, I used bronze slotted screws. Otherwise You have to remove all the studs before the regulator tube will unscrew from the bush on the front plate (smokebox end, not firebox end. It’s threaded onto a fitting at the front tube plate).

On 16 October 2024 at 10:30 noel shelley Said:

Though of little relevance yet but is there a dimension missing on Nicks drawing ? What is the thread or is it a square on the end of the regulator rod for the valve ? Noel.

It’s a square to suit the handle held on by 7 ba. As the shaft is 5/16 it’s probably 7/32 sq