Guys,
Before we get too far off track (and start a flame war), I’d like to repost the OP’s opener (coloring mine):
Oh, and Deggesty? Here is a head on of a UP 9000.
NW
And the answer begins with: do not confuse a three cylinder locomotive and boosters. A three cylinder locomotive by defnition has a third cylinder between the drivers taking steam and increasing its pressure to the main or driving wheel cylinders of the engine. Boosters are units on trailing trucks of engines and on one or more trucks of tenders, cylinders driving the wheels of the trucks. Lots have been written on both in books and magazine articles.
OBOY!
I don’t think anybody intended any insult, but this discussion has gone in two directions at once and managed to hurt some feelings in the process. Quite an accomplishment!
The misdirection is the discussion of 3-cylinder locomotives.
These were found on IHB (0-8-0’s, as discussed); UP (4-10-2’s and 4-12-2’s as discussed); SP (4-10-2’s as discussed); MoPac (2-8-2’s as discussed); DL&W (4-8-2’s); D&RGW (4-8-2’s); NH (0-8-0’s and possibly other types); and probably a few more.
The point of the question was trailing truck boosters, which were applied to an awful lot of locos in the '20’s and '30’s, but usually (not always) removed during the '40’s and '50’s due to high maintenance costs. On engines with a single trailing axle, they could not be installed on built-up trailing trucks like the Cole or Hodges, and required a cast (i.e. Delta) trailing truck. Some roads therefore used tender-mounted boosters on Mikados and engines that did not have trailing trucks, most often heavy switchers On the Akron Canton & Youngstown, Mikados 400 and 401 were delivered with Hodges trailing trucks and Franklin tender boosters. After that, no’s 402 and 403 were delivered with cast Delta trailing trucks and Franklin tender boosters to match those on the earlier engines, presumably to simplify the road’s parts inventory. In any case, the boosters were all removed from the AC&Y engines in the early 1940’s.
My 1947 Locomotive Cyclopedia shows booster engines mounted on the trailing trucks of the following:
2-8-2’s: SLSF
2-8-4’s: C&O, B&A, L&N, NS
2-10-2’s: C&IM
2-10-4’s: PRR, C.P., B&LE,C&O
4-6-2’s: B&M
4-6-4’s: C.P., C.N., C&O, NYC
4-8-4’s: C&O, C&NW, LV, SP, RDG
I am certain that this list is not complete.
&n
Another confusion factor in the question is that the booster engine would not be a single (3rd) cylinder engine (with a single cylinder there is a chance that it would come to a stop at TDC or BDC [Top or Bottom Dead Center] and thus be useless for power since it would not be able to determine which direction to turn when steam is applied). The booster engines had two cylinders at quadrature (90° to each other) so that if one was at TDC or BDC the other would be in the middle of the power stroke for the desired direction.
On the other hand… the valve gear for a 3rd (center) cylinder in the front (main) engine on the locomotive was often derived by a system of levers that combined the angles of the other two valve levers (called a “Conjugated Valve Gear”) invented by Sir Nigel Gressley. Some had a 3rd valve gear arrangement. It might even be of a totally different type, such as having Walshaerts for the two outside cylinders and Stevenson’s for the center cylinder.
On some engines the 3rd (center) cylinder was mounted higher and angled downward and the rotational spacing of the crank pins was thus set to 120°/113°/127° instead of 120°/120°/120°. Other arrangements sometimes had the center cylinder at 135° and produced a pronounced unequal exhaust beat.
As for the pressures in the cylinders…
Some engines had equal size cylinders and ran boiler pressure to all the cylinders… a “simple” engine. This produced 6 exhaust beats per revolution of the drivers.
On a “Compound” engine, the outside cylinders were fed steam directly from the boiler and were thus considered high pressure cylinders. The exhaust from them were fed to the 3rd (center) and larger cylinder which was the considered the low pressure cylinder. The exhaust from that cylinder was then sent up the stack to create the draft for the fire. This produced only
Three-cyl compounds (with one high-pressure and two low-pressure cylinders) would likely do that-- BLW 60000 did. Why would a simple 3-cyl do that? What would be the point?
There were two basic reasons to have to mount the center (3rd) cylinder at an angle.
One is because there just was not room for it to fit between the other two cylinders and the associated valve gear all in a line and have the frame members of sufficient size for rigidity. The cylinder was often cast as part of the frame itself.
The other was the need to connect the drive rod to the 2nd drivers with a sufficient strength drive rod and yet not have too large an offset crank in the number 1 axle to clear the center cylinder drive rod.
I used to have an animation of a cutaway of the setup and it was fascinating to watch the crank in the 1st axle barely miss the drive rod to the 2nd axle… Mighty close tolerances.
Back there in this in this post(age) there was a how can you get high pressure (I think that meant power) out of low(er) steam pressure cylinder?
W/O getting algebraic, say the boiler feeds 300 pounds per square inch into a cylinder which makes a piston move. At the end of movement, the pressure is 200 psi, a lot of energy left.
At that moment, the steam against the piston head originally produced power to the drivers, let the drivers roll!
Using the steam again to get the same amount of power for the same (or other, compound articulateds) to the engine’s driving wheel says to the logic god that 200 psi needs a third more cylinder surface to get the same psi against the piston head that 300 psi needs on a primary cylinder.
Many air brake valve functions relied on a greater area with low pressure working against smaller areas of higher air pressure. the differential of psi times area made things happen.
I just realized how little I know about booster operation so my questions may seem very elementary to some of you who are far more knowledgeable than me.
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I assume there was a separate throttle for the booster engine. Was it either a wide open or fully closed valve or was it possible to control the amount of steam supplied to the booster cylinder(s)?
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I believe there was an automatic cutoff device that functioned when the booster’s top operating speed was reached. How was this actuated?
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What about the possibility of wheel slippage? Was the booster engine powerful enough to cause the powered trailing truck or tender wheels to slip?
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An earlier reply contains a link to a cutaway view that shows a pinion gear that I assume is mounted on a crankshaft and engages a gear on the axle of the trailing or tender wheels. Was this arrangement common to all boosters?
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The same cutaway view shows two cylinders. Was this typical of all boosters or did some have only a single cylinder?
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How was the booster engine mechanism lubricated?
Thanks for your help in gaining a better understanding this subject.
Mark
Baron Vuillet’s account of a ride on a T&P 2-10-4 mentions the engineer letting the booster warm up with a bit of steam before they reached the foot of the hill and cut the booster in.
The booster crankshaft had a gear, and the axle had a gear; when the booster is cut in a third idler gear moves into mesh with the other two gears.
Many of the answers you want can be found here. This is an instruction manual for the Franklin booster models C1 and C2. There were subsequent improvements allowing the Franklin booster to run at higher speed, and to be reversible.
I’m not aware of a posted copy for the Bethlehem Auxiliary Locomotive (the tender booster) but [url=http://www.ebay.com/itm/