Three-Cylinder Steam

[CSSHEGEWISCH]

It seems that most railroads at one time or another dabbled with three-cylinder steam locomotives with at least two sizable fleets, UP 9000 series 4-12-2's and SP 5000 series 4-10-2's.  What was the theoretical advantage to three cylinders over two?

[tomikawaTT]

There were three reasons given for using three (or more - quite a few European locos had four) cylinders:

1. Smoother torque - think of six cylinders versus four in your rubber-wheeler.
2. No possibility of stopping on dead center.
3. Able to use the boiler's entire output without having humongous cylinders.

 

There were also some noted disadvantages:

• Valve control on the inside cylinder(s) was problematical - always more complex than that for two external cylinders.
• Lubrication of the inside rod-end bearings and crosshead guides was sometimes overlooked - out of sight and difficult to access.
• Cranked driver axles were a potential problem, especially under the concentrated stress of a third main rod with no adjacent counterweights or connecting rods.

 

The then Imperial Government Railways purchased six Alco three cylinder 4-6-2s (C52 class) and had 97 more built in Japan (C53 class.)  They were the first 4-6-2s withdrawn from service, replaced by two cylinder machines.  Apparently their theoretical advantages were more than offset by their added mechanical complexity and maintenance expenses.

Chuck

[Deggesty]

I wonder how the British overcame the disadvantages that Chuck lists. 

tomikawaTT

There were also some noted disadvantages:

• Valve control on the inside cylinder(s) was problematical - always more complex than that for two external cylinders.
• Lubrication of the inside rod-end bearings and crosshead guides was sometimes overlooked - out of sight and difficult to access.
• Cranked driver axles were a potential problem, especially under the concentrated stress of a third main rod with no adjacent counterweights or connecting rods

Or, considering the large number of three-cylinder engines used, were they convinced that the advantages outweighed all the disadvantages?

Johnny

[tomikawaTT]

Deggesty

I wonder how the British overcame the disadvantages that Chuck lists. 

tomikawaTT

There were also some noted disadvantages:

• Lubrication of the inside rod-end bearings and crosshead guides was sometimes overlooked - out of sight and difficult to access.

Or, considering the large number of three-cylinder engines used, were they convinced that the advantages outweighed all the disadvantages?

Johnny

Apparently they did consider that the percieved advantages were worth the extra bother.  So did most of the other European countries' railroads.  As I mentioned, the Japanese didn't share their enthusiasm.

The steam speed recordholder, Mallard, had a stinkbomb attached to the inside main rod bearing, which was supposed to warn the driver when that bearing was overheating.  It went off during the record run, but the driver pressed on to set the record.  When he finally brought Mallard to a stop, the bearing siezed up.

Chuck

[timz]

Deggesty

I wonder how the British overcame the disadvantages that Chuck lists. 

The fact that they accepted the disadvantages doesn't mean they overcame them. But the British had always had thousands of inside-cylinder locomotives-- which we hadn't.

[JimValle]

During the 1920's Baldwin built a massive three cylindered locomotive, No. 60000 and sent it on tour to try and interest its many customers in the concept.  This engine also featured a watertube boiler and other refinements that Eddystone was then promoting.  What the tour actually accomplished was to convince most of the targeted railroads not to go that route.  After its tour, No. 60000 was withdrawn from service and Baldwin eventually donated it to the Franklin Institute in Philadelphia where it can be seen today.  I'm not sure which element of the design was more troublesome, the watertube boiler or the three cylinder configuration but neither one caught on to any reaxl extent.  The 60000 was also a compound, the center cylinder drawing the exhaust stem from the two outside cylinders.  

[feltonhill]

 The center cylinder on 60000 was high pressure, the outside pair low pressure.

[Eightpot]

Here in the UK  just for the 4-6-2 'Pacific' type, the former LNER had over 200 locos with 3 cylinders, and from the former Southern Railway another 140. The main problem is that as the inventor of railways we made the mistakes. This resulted in a load gauge (maximum profile) for locos and other rolling stock of just over 13'high and around 9' (often less) over cylinders. Thus to get the power more than 2 cylinders became necessary. Also, not that it really affects things, but for steam an axle load of about 22 (British 2240 lb) tons was the maximum in Europe. 

 

With post-war bearing technology the problem of middle big-end problems largely disappeared from the early 1950s. On former LNER Gresley locos close inspection was done at 12,000 mile intervals. Usually they would run until the bearings were re-metalled and machined at the 24,000 mile point. A weak point was the driving axle axleboxes (plain bearings) as all 3 cylinders drove on the centre coupled axle. The solution to this was to drop this axle and replace the axleboxes - no great problem as the rods were off for inspection at this time anyway. The third part of rejuvenation came in the mid-1950s with the substitution of the double Kylchap for the previous single chimney. This gave better steaming, saved around 7 lb of coal per mile, and resulted in a freer running loco due to reduced back-pressure.The 2 to 1 valve gear was the least of the problems if lubricated properly.

During the 1950s and until the end of steam on the former LNER line out of London (Kings Cross) in June 1963, they worked the non-stop "Elizabethan" train in both directions daily from London to Edinburgh, 393 miles. Not only that, but when the first Diesels appeared, A4s often were substituted as a replacement for a failed Diesel, working that diagram. Example, London to Newcastle (268 miles), an hour or so for  servicing and head back to London.

The above is based on the writings of the former Shedmaster at Kings Cross depot, Peter Townend.

Incidentally, the new-build 'A1' post-war 3-cylinder 'Pacific' 60163 "Tornado"  has currently clocked up over 10,000 miles just hauling railfan specials.

 

Germany also went for 3-cylinder 'Pacifics' in the late 1930s with the 01.10 and 03.10 classes, several of which are still in working order for special events.

[JimValle]

I checked out the assertion that the center cylinder on the 60000 was the high pressure jug and I stand corrected..  Westing's book The Locomotives that Baldwin Built has a photo showing the steam distribution system for this engine on Page 140.  Taught me a lesson because normally in compounding the smaller cylinder exhausts into the larger one.

[wjstix]

I think the British had the advantage of smaller, lighter engines hauling shorter, lighter trains and going comparatively short distances, along with very good / excellent maintenance and repair work being the norm.