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A geared steam locomotive is a type of steam locomotive which uses reduction gearing in the drivetrain, as opposed to the common directly-driven design.

Contents

The locomotives use conventional adhesion to provide traction and therefore should not be confused with rack railway locomotives which drive a cog along a rack to provide traction.

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 tradeoff 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-grown types.

Class C Shay (three driven trucks)

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

A Heisler locomotive — note cylinder location

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. 1
  • 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" (an 0-4-4-4-4-0 type) that was also produced by another NZ manufacturer, Johnson Brothers of Invercargill.

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, but in most countries they may now be seen only on tourist lines, preservation sites and museums.

Australia

Canada

The Canada Science and Technology Museum have an operational 50 ton class B Shay Locomotive, that is in operation Sundays and Wednesdays in July and August.

Indonesia

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.

New Zealand

  • 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)

United Kingdom

About 30 Sentinels have been preserved. A few examples are shown below:

United States

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 featuring the largest remaining Shay locomotive, 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 Roaring Camp and Big Trees Narrow Gauge Railroad in Felton, California has several operational Shays, a seldom–operated Heisler and a Climax awaiting restoration.

A 65-ton 1922 Lima locomotive with 3 truck Shay design is on static display at the Traveltown open air museum in Los Angeles.

See also

References

  1. ^ "LNER Encyclopedia article on Sentinel class Y10".

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