USRA Designs

USRA Mikado Steam Engine






Type D Stoker (page 1)


The Duplex Type D
Manufactured by the Locomotive Stoker Company, Pittsburgh, PA.

(Source: 1922 Locomotive Cyclopedia of American Practices)


The real purpose of firing a locomotive by means of a stoker is to make it possible to haul greater tonnage at less cost. The stoker is applied to a locomotive essentially to obtain maximum capacity, and is not a fuel economizing device as is sometimes thought to be the case although it has been shown that fully as economical results in the way of firing can be obtained with a stoker as by hand-firing, and under ordinary conditions it has been frequently demonstrated that the same locomotive, on the same division, under exactly similar conditions, will haul from fifteen to twenty per cent more tonnage when stoker-fired. This has resulted in the application of stokers to a large majority of the heavy freight engines ordered during recent years.


The first Type "C" Street Stoker was installed in 1911, and at the present time there are over 1,500 in successful operation. The Locomotive Stoker Company, which manufactured and marketed the Type "C" Street Stoker, has developed an improved type of stoker.


The Type "D" Duplex Stoker, which supersedes the Type "C" Street Stoker, was brought out to fill the demand for a stoker that would handle both slack and lump coal, yet it does not sacrifice any of the firing principles which were developed in years of service with the Type "C" machine. The Duplex Stoker distributes coal in small particles to any part of the firebox desired, and at any rate desired. It is under the control of the fireman at all times, and can even be started and stopped by the engineer, without leaving the throttle.


Mikado steam locomotive Duplex Stoker

The conveyor and crushing system of the Type "D" Duplex Stoker after crushing the coal, carries it beneath the tender and cab decks from the tender to the locomotive in such quantity as may be required, this operation being regulated by a steam valve which controls the speed of the driving engine.


The conveyor consists of a heavy wrought steel trough in which is a heavy cast steel helical screw, a crushing zone fitted with a crushing plate, and a driving shaft secured along the outside of the trough and on the right.

The conveyor is flexibly attached to the transfer hopper by means of a ball joint, which is permanently riveted to the trough and fits into the left and right ball joint clamps bolted to the back of the transfer hopper.


The conveyor unit moves with the engine, merely resting in angle bearings in the tender. The heavy cast steel conveyor screw extends the entire length of the trough, and on the front end, a short piece of helicon screw larger in diameter than the main portion is fitted into it. This end is made larger in order to force the coal through the ball joint into the transfer hopper, the ball joint acting as a front end bearing for the conveyor screw.


The crusher or crushing zone is at the front end of the opening in the tender deck and consists of a heavy crusher with projections, set in a slide in the crushing zone of the trough. The helicon screw up to and through this zone is uniform in diameter and with the positive feed, carries the smaller sizes of coal through

Mikado steam locomotive Duplex Stoker

without crushing or breaking, but the larger lumps, forced against this crusher by the heavy steel conveyor screw, are broken to proper size for efficient firing, and will then go through the crusher and into the transfer hopper.

The conveyor drive and reverse connects the universal joint with the driving rack. This mechanism consists of a forged steel shaft, a conveyor drive and reverse gear with 20 teeth, a drive and reverse body, a ratchet wheel, three forward pawls and three reverse pawls with springs between, a shifter with yoke, a lever and catch, and drive and reverse body head. Near the front end of the shaft is secured the main gear which meshes with the horizontal rack operated by the driving engine.

A shift lever, held in forward position by a notch and easily reached through a small slot cut in the cab deck, for that purpose controls this conveyor drive and reverse, which has three positions—drive, or normal position with stoker running; neutral, or with the conveyor screw stationary while the stoker is in motion; and reverse, or with the conveyor screw reversing and pulling back the coal.