Ok, I have heard of three cylinder steam locomotives, and I know were the first two are, but were is the third one located and how did it work?
I’m no expert by any means but the way I understand it the 3rd is in between the other two in the center of the frame. I guess the axles have a crank in the middle for the connecting rods. If one of you steam experts pops in here could you explain the crank / connecting rod assembly works?
That’s correct - the inside cylinder drives a crank in the middle of one of the driving axles. Sometimes a complete extra set of valve gear was used for the inside cylinder, other times the drive for the ‘inside’ valve was derived from the two outside sets of valve gear - e.g. Gresley’s ‘conjugated’ valve gear used on the LNER Pacifics in the UK.
The problem with inside cylinders is that everything is difficult to access for maintenance, so unless there really weren’t the clearances for bigger outside cylinders (a common problem here in the UK) designers/railroads tended to avoid them.
Tony
3 cylinder steam is dead easy. Over here in Britain 3 cylinder locos were common in express engines and not unheard of in mixed traffic machines. You have two outside cylinders driving the second axle (most British 3 cyl machines were 6 coupled) and the third cylinder arranged down the engines center line between the frames driving the first or second axle. the inside cylinder will have its own inside valve gear or will have its motion derived from the two outside cylinders, as was the case with UP 4-12-2’s and SP 4-10-2’s, both using the British Gresley valve gear. The cranks are all set at 120’’ to each other giving a very even turning moment and 6 exhaust beats per revolution resulting in a more even pull on the fire.
So how does the crank connect on the middle cylinder? On a normal cylinder there is a connecting rod (piston to one wheel) and a wheel to wheel rod. The only way I can visualize the middle cylinder is that it connects to the front (drive) axle (cylinder - wheel rod)
…Surely one would think the middle cylinder would be connected via piston rod and necessary mechanicals to a crank in the first driving axle. Of course all the wheel sets would be connected via the outside rods. These are my thoughts, but for sure, no expert.
The middle cylinder is connected to a crank and the wheels are connected by the outside coupling rods. Most British 3 cyl engins had the drive concentrated on the 2nd axlebut some drives were divided. The crank axle was usualy build up in several parts with the axle in two parts with a crank web pressed & keyed to each half with a crank pin between them. The middle big end is nesesserally split and is either a Marine big end with a strap held to the con rod by forged studs and nuts, or it is a forked De Glen style big end with the bearing brasses heald in place with a wedge and cotter, or a wedge and locking nuts. Marine big ends are simpler, but have been prone to overheat and De Glen big ends seem to give the best overall performance.
For a view of the cylinder casting of a 3 cylinder locomotive (Baldwin 60000)
http://www.cwrr.com/Lounge/Reference/baldwin/fig7.jpg
And the driven axle
http://www.cwrr.com/Lounge/Reference/baldwin/fig10.jpg
I couldn’t find a shot of the frame center after it was assembled.
Thanks Tom
In the US, at least, the middle cylinder rarely if ever drove the first axle. So it had to be inclined, maybe 8 degrees from horizontal, and likely the first axle had a bend so it would clear the inside rod to the axle behind it.
Since it was inclined, but the Gresley-Holcroft gear was designed to give valve events 120 degrees apart, the cranks were spaced 120-112-128 or some such thing.
That’s assuming we’re talking about a 3-cyl simple engine. A 3-cyl compound like the Baldwin 60000 will have the outside cylinders the usual 90 degrees apart, since they’ll usually be the only ones exhausting up the stack.
Firstly, that picture of the 60000’s cylinder casting is neat. That casting probably weighs at least 20,000 lbs.
Notice to the upper right of the center cylinder is the piston chest for the middle cylinder.
The 9000 class had their crankpins 120-120-120. Later, some had their center Gresley Conjugating Mechanism (GCM) replaced with a center Walschaert’s valve gear.
In the US, ALCo had the patent rights to the GCM, and because of this, ALCo produced most of the three-cylindered locomotives in the US.
Sincerely,
Daniel Parks
When they still had Gresley/Holcroft gear, you mean? So the three pistons wouldn’t reach front-dead-center 120 degrees apart? Did they somehow modify the valve gear to allow that?
Because the center piston would be at an incline, it would reach its most forward point a few degrees off of 120. I wish I knew more, but sorry, I don’t [:)].
Sincerely,
Daniel Parks
weren’t all the drive axels on a 3 cylinder locomotive connected with the third cylinder?
They almost have to be attached to the front driver set. Note the incline of the center set of cylinders in my linked photo (you’re looking at the back or the part that faces the drivers). Bending the axle on the first set for clearance wouldn’t work, the wheels and axle are a rigid assembly, the bend would oscillate up and down with the rotation of the wheels and hit the rod.
No, because the rod is connected to a similar “bend”, the crank, and the axles are coupled together, so the bend in the front axle exactly duplicates the movement of the crank and the connecting rod. When the bend is down, the rod is down, and when the bend is up, the rod is up too, and it is all calculated so there is clearance through the full 360 degrees.
Some locomotives did, of course couple to the lead axle, but I can’t remember whether Baldwin 60000 does. It is in the Franklin Institute in Philadelphia, so anyone nearby can go and check. It is worth the effort, particularly the way the two valve gears sit on one side.
M636C
With those photos of the awesome castings and the internal crank on the drive wheel set…I would believe it {the 3rd cyl.}, has to be connected to the first drive wheel set…Can’t see that there would be room to do it any other way…
The castings on the Australian D57 4-8-2 had the same angled centre cylinder but they had a bent lead axle and all three cylinders drove the second axle, because there were balancing advantages in doing this. They had Gresley conjugated valve gear. There were special instructions saying that if the lead coupling rods were broken, the lead axle had to be raised clear of the track so it wouldn’t rotate because the bent axle wouldn’t stay in synch with the others and the bend would hit the rod, as Tom indicated. While I can’t remember 60000, I have drawings of the D57 and they show all three cylinders driving the second axle. Remember that the centre angled cylinder is raised above the other two. If it drove the lead axle, it could be parallel and in line with the others. the reason it is raised is to give clearance to the rod over the lead axle, even with the bend. Another Australian loco, H220, drives the lead axle with the centre cylinder, and its centre cylinder is a separate casting placed forward of the outer two, but at the same level. There is a large hole between the outside cylinders to allow the rod to pass between the outer cylinders. H220 is a 4-8-4 similar in size to the D57, but both of these are smaller than 60000. Another thing to notice is that usually, the valves are all horizontal whether or not the cylinders are at an angle.
M636C
The locomotives using a double Walschaerts valve gear to drive the valves for the middle cylinder had two sets on the right side, with an offset eccentric crank.
Alco was the only US builder licensed to build the Gresley valve gear, so Baldwin had to use either a double Walschaerts (on the D&RGW 4-8-2s) or a Joy Valve Gear (somebody’s big 0-8-0 switchers) to drive the middle cylinder. The UP 4-12-2s that lost their Gresley gear had a double Walschaerts on the right side.
AFAIK, no three-cylinder locomotive had the center cylinder connected to the lead driving axle. I believe that the Rock Island had some four-cylinder simple Atlantics that had the center cylinders driving the first axle. The Santa Fe’s Bull Moose Atlantics were also; they might have been three cylinders, but I believe they had four and were compounds.
The Baldwin 60000 had regular Walschaerts on the left side, and had a connection from the crosshead that drove the link on the right side, somewhat in the manner of Young valve gear. The center cylinder got its motion from a Walschaerts eccentric crank and link on the right side. The two outside crankpins were at 90 degrees, with the center crankpin 135 degrees from both. The outside cylinders used outside admission valves, so that the exhaust from the center cylinder (which was inside admission) could go in a straight line to the intakes to the outside cylinders. It may have been the last locomotive built in the US with outside admission valves.
Old Timer
Old Timer
I’m guessing nobody can find a US 3-cyl engine (built after 1920, anyway) that drove the lead axle.
Some 4-cyl engines did, but even some of them drove the second axle with the inside cylinders. And I don’t think their inside cylinders were inclined, either-- so the inside rods had to reach around the lead axle. Some SFe 4-6-2 compounds were built that way.