It may have absolutely no relevance at all to the Suffolk Tractor, but the next two boiler designs by John Haining that appeared in the ME both had working pressures of 85 psi. One was made in copper, the other was steel.
Not to have the working pressure on the drawings seems to be a serious omission, I could find no further references to the Suffolk Tractor after the one in vol 147 issue 3664. As there have been a number of these models built, someone must have this information, I hope that it was not an inspired guess.
While it is possible to recalculate the working loads, without knowing what factors John Haining took into account in his original calculation, it may be frustrating work. Perhaps someone with access to some FE software might like the challenge.
Are new designs of boiler published in the ME accompanied by a set of the designer's calculations so that boiler testers can see what assumptions have been made or do we just go on trust?
Neil