Here's a bit of artwork from "Red Devil" which might help illustrate the Tross staybolt and the "standard" installation of the fillet welded rigid stay per European practice. Wardale was recommending the use of the Tross stay as sunken rather than installed proud of both sheets, like the standard shown, to allow for the installation of other hardware in the firebox. His experience with these stays was in South African practice, but he was working on modernizing Chinese QJs. Most interesting combinations of stuff since he talked about the combination of the Tross stays with the German "balloon boilers" as Matt and Matt explained in another thread, and using them to sort of provide a buffer zone of stays that would forgive flexing more than rigid stays in the zone between the rigid stays / mud ring and the traditionally flexible stayed areas in the QJs.

So, leaving the sunken installation idea aside for the moment, might this have merit in cases where the rigid stays close to the flexible stays frequently crack or loosen in American practice, and would it be permissible if it would be of benefit?

dave

My personal opinion on the new design shown above is the sharp edge of the hole exposed to the effects of the fire will overheat and fatigue at an advanced rate, the reduced section staybolt has already proven itself to be a better design, fillet welded bolts are a more cost effective installation but I reserve opinion on them until I can do more research. The engineering that others have uncovered supports their use, but I would like to know more about how they hold up over the long haul. I also have issues with the crevice left by the nonwelded portion of the bolt passing through the sheet, similar to what happens with flexible bolts and sleeves in the lower portion of combustion chambers. I wish we could see more info from the newly constructed boilers that have required some retrofitting, so we can learn from others who have been bold enough to try out some of the ideas generated by the last generation of steam designers and engineers. Remember, the largest failure of all is to have never tried at all. Of course the costs of failure must be accounted for at some point and could probably be absorbed by a mass production factory, but would be a hardship on most preservation groups.
My 2 cents,
Mike Tillger

One of the interesting concepts of the sunken fillet weld is to place the weld in a neutral axis - that is, to keep the sheet from wanting to arch inward towards the welds as a field of them is applied. This was one of Tross's latest recommendations. With a little dressing, the edges would not be a problem.

The consideration of this design will likely not be possible until we move to design by analysis instead of design by rule.

Playing devils advocate here, but aren't some of the rules the result of when analysis failed and experience took over. I know there has been great advances in analysis methods used today. I have experienced a multitude of machinery that looks good upon mechanical analysis but could not be made to function in the real world in the R&D department I worked in. Somewhere there lies a compromise, which I guess is called the factor of safety. As design analysis becomes experienced, the factor of safety is lowered, this is what is happening in the real world of power boilers being driven also by competition and cost effectiveness. I welcome these advances in boiler technology, but I also believe there is a risk mixing the old with the new in locomotive boilers. I would be more acceptable about using design analysis in new construction than in replacing a new boiler on an old chassis, account I could design the rigidity of the frame first, so as to limit the frame flex from passing on to the boiler and adding to the fatigue load of the boiler materials.
Again my 2 cents,
Mike Tillger

Mike, I totally agree with design by rule, but that does not appear to be the future.