Geared steam locomotive
Explanation and rationale
The steam locomotive, as commonly employed, has its pistons directly attached to cranks on the driving wheels; thus, there is no gearing, one revolution of the driving wheels is equivalent to one revolution of the crank and thus two power strokes per piston (steam locomotives are almost universally double-acting, unlike the more familiar internal combustion engine).
The maximum rotational speed is fairly fixed for a given engine technology. Given the lack of any variable-ratio transmission between the piston engine and the wheels, the designer is forced to compromise between desired torque and desired maximum speed; the radius of the driving wheels determines this. The radius of the crank affixed to the wheel is of course less than this; its radius determines the length of the piston stroke. This cannot be too large, for the locomotive will be unable to generate enough steam to supply those large cylinders at speed; it cannot be too small, or the starting torque and thus tractive effort will be too small, and the locomotive will not be able to start a train.
Many applications required a low speed locomotive with ample starting tractive effort – industrial use, mines and quarries and logging operations, steeply graded lines and the like – especially when the track is cheaply built and not suited to high speeds anyway. Unfortunately, although the trade-off of speed versus torque can be adjusted in favour of torque and tractive effort by reducing the size of the driving wheels, there is a practical limit below which this cannot be done without making the piston stroke too short on a directly driven locomotive.
The solution is to separate the crank from the wheels, firstly allowing for a reasonable piston stroke and crank radius without requiring larger than desired driving wheels, and secondly allowing for reduction in rotational speed via gearing. Such a locomotive is a geared locomotive. Most were and are still single speed, but some did employ a variable-ratio gearbox and multiple ratios.
Types of geared locomotive
The vast majority of geared locomotives in the world were built to one of three distinct designs, whether licensed and official, or clones built after the expiration of key patents. Of the types, the Shay locomotive was the most numerous and best known. The overwhelming majority operated on the North American continent, but with a number in use in various parts of South America and a fair number in Australia and New Zealand, including home-developed types.
It should be noted that these were not the first locomotives to use geared transmission. Richard Trevithick's Coalbookdale Locomotive used a large gear instead of side rods to link the crankshaft to the driving axles, with a net 1:1 gear ratio. The early Grasshopper (1832), Crab (1837) and Mud Digger (1842) locomotives built for the Baltimore and Ohio Railroad used gear ratios on the order of 2:1 so that each turn of the crankshaft caused about two turns of the driving axles. This allowed use of relatively small driving wheels without sacrificing speed.
The Shay locomotive
The Shay locomotive features an offset boiler with a multiple-cylinder engine affixed to it on the opposite side, driving a longitudinal shaft geared to the axles via bevel gears (see also Ephraim Shay, inventor).
The Climax locomotive
The Class B Climax locomotive, has two inclined cylinders driving a transverse crankshaft, geared to a longitudinal driveshaft placed centrally on the locomotive and driving the powered trucks via internal gearing.
There was also an earlier Class A Climax with a vertically mounted marine-type steam engine, working through a similar drive-line, via a two-speed gearbox.
The Heisler locomotive
The Heisler locomotive, has a 'Vee-Twin' style steam engine, one cylinder each side of the boiler, affixed to a centrally located longitudinal driveshaft, again geared to the wheels.
Clones and Variants
Besides the three main designs mentioned, there were other designs and clones:
- The Willamette locomotive was an improved-upon clone of the Shay locomotive produced in limited number by Willamette Iron & Steel (better known for their steam donkey engines) after key patents expired. West coast logging customers were clamoring for improvements in detail design and the application of more modern locomotive technology to the geared locomotive; Lima (manufacturers of the Shay) were dragging their heels. The Willamette was the response to that.
- The Kitson-Still locomotive used different ends of the same cylinders for steam or diesel propulsion. The crank was above the frame and a gear train of fixed reduction linked it to the centre axle.
- Aveling and Porter built some geared locomotives which were, essentially, traction engines with flanged wheels. The early ones used sprocket chain drive but later versions had spur gears.
- The Avonside Engine Company produced a small number of narrow gauge geared steam locomotives for sugar cane plantations in Natal. These were similar in design to Heislers.
- The Sentinel Waggon Works built numerous geared shunting locomotives to several designs. These combined high-pressure boilers with high-reduction gearing to provide high torque at low speeds.
- A & G Price of Thames, New Zealand built a number of geared locomotives, often home-grown variants of the Climax A, Climax B or Heisler types. They did however produce a type that is known as the "16-wheeler" (0-4-4-4-4-0) that was also produced by another NZ manufacturer, Johnson Brothers of Invercargill. Price's last steam engine was a Heisler locomotive, built 3 years after the last American Heisler was built.
With the decline of the commercial use of steam traction, the commercial use of geared locomotives has similarly reduced.
Some geared steam locomotives are still at work in the sugar plantations of Indonesia, and no doubt elsewhere too, but in most countries they may now be seen only on tourist lines, preservation sites and museums. The particular advantage in cane sugar operations is the ability to use the dried solid residue of pressing the cane (see bagasse) as a fuel of trivial cost, providing that low cost technical labor is available to maintain the locomotives.
- Puffing Billy Railway in Victoria, Australia:
The Canada Science and Technology Museum in Ottawa, Ontario has an operational 50 ton class B Shay Locomotive, that is in operation Sundays and Wednesdays in July and August.
The British Columbia Forest Discovery Centre @ Duncan, British Columbia. Shays - Lima shop numbers 2475 (display) and 3147 (out of service pending boiler work). Climax shop numbers 1057 (display) and 1359 (operational).
Wide variety of types still in use at sugar mills. Most are long wheelbase 0-8-0 locomotives that use an articulation technique incorporating a geared drive to the outer-most axles, the inner pair being direct-drive.
- Shantytown, West Coast:
- Heisler, makers no.1494 (unrestored)
- Climax, makers no.1203 (under overhaul)
- The Pukemiro Line, Pukemiro:
- Heisler, makers no.1063 (unrestored, parts supply)
- Heisler, makers no.1082 (awaiting overhaul)
- Climax, makers no.1650 (unrestored)
- Price Cb 117 (Class A Climax clone, restored)
- Price E 111 (Class B Climax clone, unrestored)
- "Steam Scene", Christchurch:
- Price V 148 (Heisler clone, under overhaul)
- "Ferrymead Heritage Park", Christchurch:
- Heisler, makers no.1450 (unrestored)
- Price Cb 113 (Class A Climax clone, restored)
About 30 Sentinels have been preserved. A few examples are shown below:
- Buckinghamshire Railway Centre:
- two Aveling & Porters
- two Sentinels
- Embsay and Bolton Abbey Steam Railway
- one Sentinel
- Northamptonshire Ironstone Railway Trust
- two Sentinels
No geared steam locomotives remain in commercial use in America. However, several are in operation on tourist lines.
The Cass Scenic Railroad State Park in West Virginia uses only geared locomotives, and features the largest remaining and last Shay locomotive ever built, the 162-ton former Western Maryland Railway #6. The railroad also owns a Climax locomotive and a Heisler, enabling all three types to be seen.
The White Mountain Central Railroad at Clark's Trading Post in Lincoln, New Hampshire, operates Climax #6, built in 1920 (builder number 1603), on its tourist line. Clark's also has the last remaining Shay in New England. The Shay is non-operational but in storage. Clark's also has a 32-ton Heisler locomotive that is awaiting staybolt replacement.
The Southeastern Railway Museum in Duluth, Georgia, has a two-truck Heisler (#9) lovingly restored on static display inside the main exhibit hall. The Heisler is painted for the Campbell Limestone Co and is in excellent condition.
At the Mount Rainier Scenic Railroad in Washington state, a 99-ton West Fork Logging Heisler #91 is operational, a 70-ton Hillcrest Lumber Climax #10 is operational, a 95-ton Pickering Lumber Shay #11 is awaiting boiler work, and a 75-ton Rayonier Company Willamette #2 is operational and is the only Willamette operating.
- J. Snowden Bell, The Early Motive Power of the Baltimore and Ohio Railroad; see chapters I and IV.
- "LNER Encyclopedia article on Sentinel class Y10".