This gearing is part of the machinery within the locomotive and should not be confused with the
pinion that propels a
rack locomotive along the rack between the rails. The geared steam locomotives that have been built have been for conventional track, relying on the
adhesion between wheels and rail.
Unlike conventional steam locomotives, they are not classified by their wheel arrangement. Instead, they are classified by their model and the number of trucks they have.
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 available starting torque and thus
tractive effort will be too small, and the locomotive will not be able to start a train.
Many industrial applications require a low speed locomotive with ample starting tractive effort. These industries range from mining and quarry operations to forestry and
logging operations. Steeply graded lines, especially when the track is cheaply built and not suited to high speeds, will also favour the usage of a locomotive with a high tractive effort. 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 region, 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.
These were not the first locomotives to use geared transmission. Richard Trevithick's
Coalbrookdale 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.[1]
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
Classes B and C
Climax locomotives have 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 '
V-twin' style steam engine, one cylinder each side of the boiler, affixed to a centrally located longitudinal driveshaft, again geared to the wheels.
Other types
Besides the three main designs mentioned, there were other designs and clones:
The
Sentinel Waggon Works built numerous geared
shunting locomotives to several designs mainly with vertical water-tube boilers and high-speed, enclosed, poppet-valve engines. These combined high-pressure boilers with high-reduction gearing to provide high torque at low speeds.[2]
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.
Davenport Locomotive Works held a series of patents for
gearboxes designed to ride between the locomotive frames of side-rod locomotives, the first granted in 1913, had open gearing.[3][4] Later improvements had fully enclosed gears.[5][6][7] This was offered as both a single-speed and two-speed transmission, and it was used in four-coupled and six-coupled side-rod locomotives, with the
crankshaft input to the gearbox just behind the rear
driver.[8] Larger
articulated locomotives were built with 2 4-coupled geared trucks, with the cylinders at the inboard ends and gearboxes outboard.[9] Davenport advertised these locomotives for industrial, quarry and logging use.[10]
The
Bell Locomotive Works sold a line of small industrial locomotives based on modular, fully enclosed 2-cylinder "steam motors" geared to the drive axles.[11][12][13][14]
A & G Price Ltd 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.
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
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.
In 1899, the Wiener Lokomotivfabrik, Floridsdorf, Austria produced the narrow gauge geared steam cog locomotives operated on the
Achensee Railway.
Vertical boilered "coffee-pot" locomotives were often geared, though those made by
De Winton were not.
Today
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[citation needed], 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.
Class B Climax 1694. Purchased by the
Forests Commission Victoria in 1928 for hauling logs on the Tyers Valley timber tramway which branched off the
Moe-Walhalla railway east of Melbourne. After decommissioning the locomotive in the early 1950s it was stored (abandoned) at the State Sawmill site at
Erica until it was transferred to
Puffing Billy's museum for static display in 1965. Restored to steam by the Puffing Billy Railway in the 1980s. A major overhaul has been finished and it returned to service Sunday 8 September 2013.[15]
Lima-built Shay locomotive from the
Ali-shan railway in
Taiwan, although it has not yet been restored.
Wide variety of types still in use at sugar mills. Most are long wheelbase
0-10-0 locomotives that use an articulation technique incorporating a geared drive to the outer-most axles, the inner pair being direct-drive.
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.
A 65-ton 1922 Lima locomotive with three-truck Shay design is on static display at the
Travel Town open-air museum in
Los Angeles.
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.
The
Hesston Steam Museum in Hesston, Indiana has an operational
Shay locomotive that was first restored in 1975. It was severely damaged in the 1985 fire, but restored again between 2000 and 2006 in time for the foundation's 50th anniversary. Restoration has since continued, and "The Big Shay" will begin offering rides to museum patrons the weekend of August 5, 2023.
^Davenport Locomotive Works, Advertisement,
The Timberman, Vol. XXV, No. 7, (May, 1924); page 189. The same ad appears on page 189 of the July, Aug., Sept., and Oct. Issues.