Re: Boiler Pressure

As to the mention of the cylinder oil not holding up well under high heat, remember that Superheat temp can be a variable & not a constant, even if the boiler pressure stays the same. I don't have my table in front of me, but I'll quote the one that I can easily remember...Saturated steam temp @ 200 lbs. is 388 degrees F. I've personally seen GCR's 4960 (at 200 lbs.) with around 700 degrees F steam temp...that's over 300 degrees of Superheat. This was when the locomotive was being worked hard with a tonnage train AND the Superheater was kept clean by frequent sanding. This figure dropped significantly when we topped the hill @ Apex (now Imbleau) and drifted down into Coconino Canyon. Yes, sometimes you find yourself right near the limit of breakdown with cylinder oils.
I'll disagree a bit on the comment about not being able to have a 4-4-0 with a high pressure boiler. I believe that you could; you'd just have to reduce cylinder size to compensate for this.
I think that one reason that not many smaller locomotives had really high pressure was because of the greater weight that would come with thicker sheets & a larger number of stays. I could stand corrected on this one though.