Three cylinder steam engines

Sam,

"Quartered" at 120 degrees so 6 even strokes per revolution.  Third cylinder and piston attached to crank axle.  Well covered in both of Kratville's books on the UP three cylinder power.  Also Boyngton's (SP??) on the SP 4-10-2s.

ChipR

Here's a diagram of the valve gear on a 3 cylinder Bulleid pacific locomotive. Although his design is chain driven, it is based upon the same principal as Walschaerts valve gear.

http://upload.wikimedia.org/wi...chain_valve_gear.svg

Well 120 degrees makes sense but then I am not a mechanical engineer so thought maybe they "played tricks" with how the third cylinder worked to add power while retaining the wheel quartering.  So then the drive wheel crankpins are 120 degrees apart rather than normal 90.

Hi,

unfortuantely I do not have software to open the .svg file.

What browser are you using? It opens just like any other page in Safari. 

Anyway, here is a screen-shot of the page. I hope it may help.

There was a real practical purpose to the 3 cyclinder design as it greatly reduced the stress on the rails and yielded a smoother power curve.  Also lighter weight reciprocating parts.  Porta proposed a three cyclinder compound industrial unit with the third cyclinder using reheated steam.  Unfortunately, in did make things more complex and most mechanical departments just didn't want to deal with it.

All three cranks were set 120 degrees apart. 

It's interesting that the Southern Railway Pacific whose diagram is shown should not have used Sir Nigel Gresley's "conjugated" valve gear which consisted of levers mounted ahead of the cylinders to drive the valve for the middle cylinder.  These levers took their motion from the extended valve stems of the two outer cylinders.  This was a much simpler arrangement than the chain-driven monstrosity shown above.  

Alco had the US license to produce the Gresley valve gear, and all their three-cylinder locomotives used it.  Baldwin did not have this license, so its few three-cylinder locomotives used other arrangements.  Some used a Joy valve gear on the inner cylinder, others used a double-Walschaerts arrangement with the inner cylinder driven by a second valve gear on the right side of the engine.

The exception to the 120-degree setup is the Baldwin 4-10-2 experimental engine now in Phildelphia's Franklin Institute.  Its driving wheels are quartered with a left-hand lead, and the center cylinder crank is 135 degrees from both the outer cranks.  The valve gear on the left side is a normal outside-admission Walschaerts; the right side Walschaerts link takes its motion from the left crosshead, and the link for the center cylinder is driven by a crank from the right side. which has a seeminlgy strange orientation.

EdKing

Three-cylinder engines looked good on paper but everything had to work together precisely. Cast frames and roller bearings reduced stress on their running gears. Most three-cylinder locomotives had neither. Only the final UP 4-12-2's had cast frames, and all had solid bearings. Roller bearings were finally applied to Gresley valve gears. As solid bearings there wore down (or wore out), valve events moved "out of time" and made everything worse. By the time maintenance costs began to rise, the UP had 88 4-12-2's. During the Great Depression they could not be retired or replaced. As better times came, they were replaced by Challengers with the same number of drivers but with all rods and valve gear outside. They didn't need a crank inside on an axle for a third main rod.

   Three-cylinder and four-cylinder locomotives were popular in England and Europe, and some are still running. Many had separate throttles for inside and outside cylinders. It seems to me that they were smaller than their American counterparts, and that reduced stresses on their running gear - enough to make them practical and popular.

Three cylinders make good sense from a mechanical standpoint for more even delivery of power. Unfortunately the center cylinder is more inconvenient to access for maintenance and servicing.

Three cylinders allow better balancing for speed because the cylinders and rods can be smaller compared to a two-cylinder of equivalent power. The fastest steam locos, English 4-6-2 Mallard and German 4-6-4  05002, where both three cylinder designs.

Monstrosity! How can you say such a terrible thing?  Oliver Bulleid was a top notch  engineering genius, and his designs were quite visionary. The chain driven valve gear was an extremely elegant solution which enabled the valve gear to be contained in a sealed oil bath enclosure within the frames of the locomotive. This reduced maintenance requirements quite considerably. There were a few teething troubles (Not helped by there being a war on at the time.) but these were quickly solved, and proved to be very reliable in use.

For mechanical elegance, a four cylinder balanced compound. Note the smaller rods and small wheel weights in non-standard locations.

I wonder why Alco never married its 3-cylinder designs up with the SuperPower concept.

The early 63" drivered 2-8-4s and 2-10-4s were hard on the track; dividing all that power up with three cylinders and reducing the weights of the reciprocating parts might have been a big help.

EdKing

My reading indicates that Bulleid departed as far as possible from his

predecessor's work.  If I recall correctly, he was passed over when British Rail was formed.  There were more than a few fires from leakage of the enclosed oil bath.  However, I do think the Battle of Britain class Pacifics are elegant looking.

ChipR 

I have read the SP 4-10-2's tended to cut livers out of the track when working in the mountains.  At night, people could see bright "worms" coming off the track.  What would cause that?

Anyway, SP moved them for mostly flatland operation.

Overly long wheelbase for the curves, flanges attacking the railhead?

Hi ChipR,  When Bulleid took over as CME at the Southern, he inherited a large collection of rather outdated designs that were firmly fixed in the 19th century. So yes, I would agree that he departed a long way from Maunsell's designs, as he was tasked with modernising the Southern. Before joining the Southern, he was working with Ivatt and later Gresley at the G.N.R, and subsequently the L.N.E.R. Whilst there he played a significant role in the design of such locomotives as the A4 pacifics. (His wife Marjorie, was Ivatt's youngest daughter.)

He wasn't 'passed over' by British Railways following nationalisation, but was appointed as CME of the Southern Region. He introduced several new designs in this period, but the restrictions upon innovation that BR imposed were not best suited to him. So in 1950 he moved to Ireland and became the CME of CIE, where he introduced modern diesel power to their fleet, leading the modernisation of the Irish railway system. He stayed there until he retired in 1958. All in all, he was a remarkable man and had a very distinguished career.   

I remembered this Alco switcher engine at St Louis Museum of Transportation.

see links

http://transportmuseumassociat...lton_Southern_12.htm

http://transportmuseumassociat...ail_motive_power.htm

The 3rd cylinder was not easy to observe. Tucked under the smoke box area.

My snoopy friend--crawled under frame to check it out.It's a rusting hulk now and needs some TLC.

Sorry -no pics.

Floyd

The Indiana Harbor Belt had huge 3-cylinder 0-8-0's with boosters on a tender truck. AHM imported some O scale plastic models years ago. A motorizing kit was available, too.

Eventually they were converted to 2 cylinders. But the third cylinder was visible under their smokeboxes.

Me likes three cylinder steam: