Is it possible that the reason for the “stuttering exhaust” of an SP 5000 was the 28 inch stroke on the inside cylinder vs. the 32 inch stroke on the outside two? Even if the exhausts were essentially synchronous, there would be a smaller volume of steam exiting from the center cylinder and this would tend to soften the sound and thus make it sound like it were “stuttering”. If the bore and stroke were the same, each of the three cylinders would be consuming the same amount of steam with any given cutoff and doing equal amounts of work. However, with a shorter stroke, the inside cylinder is doing less work than either of the 2 outside ones.
The reason I ask this is that I had thought about pointing out that Shays have a synchronous exhaust (but someone would argue the cylinders are in the same plane) when it occurred to me that the SP 5000’s had an inside cylinder shorter in stroke than the outside. This is unlike the “Flying Scotsman” (or a Shay), all 3 of whose cylinders of. of the same stroke.
Hmm. OK, I’ll buy the 120 degree crank settings vs. 90 on the outside and 135 on the inside.
But I’m still taking a protractor to the drawings in Boynton’s book.
Mike
Notes to the uninitiated:
Shay locomotives for the most part were built with 3 cylinders.
“Flying Scotsman” was a British 4-6-2 designed by Nigel (later Sir Nigel) Gresley, who also invented a method whereby 2 sets of valve gear could control steam admission and exhaust events in 3 cylinders.
I believe the irregularity was due to varying valve settings due to an inherent problem with the Holcroft -Gresley valve gear, a problem that Holcroft outlined to Gresley during their meeting where Holcroft explained about keeping the valves in one plane, while the cylinders were not.
The basic problem is that the outer valve rods, which drive the conjugating mechanism, expand as they heat up, moving the valves very slightly forward relative to the valve gear. Unfortunately, the conjugating gear drives the centre valve from the front, and the heating of the rod moves that valve towards the rear. All locomotives with Holcroft -Gresley gear have this problem, except the two British Southern Railway locomotives built with external links connected to the valve gear rather than the valve rods.
Some of Gresley’s A4 Pacifics had the centre cylinder lined up to 17" diameter (from 18") because the valve gear irregularity increased the power output of the centre cylinder and overloaded the centre big end. Early knowledge of this problem might have suggested a shorter stroke for the inside cylinder, although the reduced size of the crank throw is a more likely reason.
Certainly, the German 012 class Pacifics, with three separate sets of valve gear had a very even beat, which backs up the valve gear as the cause.
Interestingly, Henschel in Germany had developed a conjugating gear in 1915 that did not have this problem, before the Holcroft-Gresley design was developed, and maybe five times as many locomotives used the Henschel gear as ever used the Holcroft-Gresley design. I suspect that a lack of foreign language skills in the British engineering profession may have been the cause of this wasted effort.
As I heard it, the principal cause of the problem with the Gresley conjugated drive was that any slack in the levers (or shaft whip in the ingenious Australian adaptation) became magnified at the center valve, resulting in overtravel. The “expansion” tendency would then further distort the valve events… hmmm, probably less bad effect with long-lap, long-travel valves a la Churchward, perhaps?
I had also understood that part of the problem with American simple three-cylinder engines was that the inside valves were difficult to set in the first place (particularly, if Railroad Magazine stories are any indication, the SP engines <;-P) – while quarter on the outside drivers would have been easier and more familiar.
Where is this thread far, far away? I’d like to see precise details before making more stupid assumptions or comments…
In Union Pacific Steam by Kratville & Ranks, the authors state that UP 9000’s as built had the exhaust from the center and one of the outside cylinders combined before going up to the smokebox. Some were modified by UP to make them seperate. Others were fixed when the engines got cast cylinders and sub-frames. I’m not sure about the SP 4-10-2’s but they were all built by Alco and this could also affect the sound.
I’ve never heard a 9000, but always wished I could. I’ve pretty much assumed ‘off-beat’ refered to the difference between 90 and 60 degree engine designs. 3, 6, and 12 cylinder engines have a very distinctive sound compared to 4, 8, or 16 (for example an air-cooled 6 cylinder Porsche compared to a VW Bug 4 banger, or a 12 cylinder Ferrari compared to an 8 cylinder anything else). Maybe someone on the forum knows why(even vs. odd harmonics in the sound???)
Hmm…and here i thought this topic was something different, as in “Hints That You As A Railfan Need A Shrink:” 1) you make comments on a forum then back them up using other screen names, 2) you advocate train hopping, ect. [:0]
but then again, this is a good topic too… steam is always a good topic [;)]
I’ve probably spent as much time trying to find out about women, but I get less consistent answers and fewer established facts. So no I don’t know as much, but it is good fun trying to get the answers (but carefully). But any man who claims he fully understands women is really a candidate for psychiatry!
Given my location in the world, I see some late night postings. I’m sure there was a thread with six or so postings obviously by the same person under two names. If you really want to talk to yourself, why use a forum?
That wasn’t good. You must know about one of the genders or else you’re neither. But I shouldn’t have said this 'cause it could stir up future controversy with the almighty rumproast.
