Mechanical Stokers

[Derek Walker]

I am curious about those mechanical stokers used on the steam locos. What drives the unit, I presume it cannot be used to fire the boiler until there is actually steam up, is it driven through some sort of gearing to the wheels? or is it electrically driven? or even steam driven. Does it spread coal throughout the boiler or must it be manually raked across the fire? Is it "always on" or can it be switched on and off? and, most importantly, is it more efficient than a manual stoker who can gauge the fire with his eyes and decided where more coal is needed and where there are cold spots.

[Nathan Berelowitz]

The mechanical stoker only works when the locomotive is in steam. It consists of a motor mounted in the tender on the Firemans side (class 15F,23) and if you look at a photo side on, you can see the inspection cover on the tender corner.
The motor is coupled by gears to a long shaft running to a gearbox from which the conveyor shaft is coupled and this shaft which is turned like a shaft inside the mincer machine, runs on the lowest part of the tender coal space in a trough. The trough is covered with sections of metal plate called slides, and they are abled to be pulled forward as the coal gets used in the tender, so that it will continue to fall in the conveyor trough.

The forward end of the trough in the has a crusher unit that will break the coal down to a smaller size.This is a cast piece of steel with some prongs on it which break it down. It does not move in itself, but as the coal passespast it, so the action happens.

The coal is conveyed by the conveyor screw up into the firebox, where it falls onto a cast iron distribution table with raised ridges on it. These ridges enable the coal to fall and be blown by the steam jets to the various parts of the firebox. The steam jets are in the table just above the ridges as mentioned. There are 5 jets controlling the coal
distrubution. Left back, Left front,Fine coal, right front and right back.
The fireman has the operating controls in front of him and sets the various jets to try get an even distribution of coal over the firebox.

Our 15F 3117 is mechanically fired, but this last trip, we hand fired her on the Tshwane Xplorer train to save on coal and keep fit!!

[John Ashworth]

The mechanical stoker motor is driven by a small steam engine of its own in the front of the tender. The speed of the motor is controlled by a steam cock on the fireman's side. You are correct, Derek, that it only operates once there is steam pressure. While lighting up, the loco must be fired by hand.

The worm of the stoker delivers partially crushed coal to a table plate just inside the firehole door, and there are five high pressure steam jets which then blow the coal to where it is needed in the firebox. These are controlled by cocks on the fireman's side.

Both the motor and the steam jets can be switched on and off as needed. The motor can also be reversed to clear blockages.

Whether it is more efficient or not than firing manually I will leave to the old firemen to answer. I think locomotives get to a size where it would be impossible to hand fire (eg a US Big Boy). However on something like a 15F you can definitely hand-fire and almost certainly use less coal than the mechanical stoker would. Nathan and Whitey hand-fired 3117 last Sunday.

Hand-firing a mechanically-stoked loco is a little awkward as the fire-hole is at the wrong height, the worm in the middle of the footplate means you can't stand where you want to, and the fire-hole door is a flap type which gets in the way of the shovel. However you can shovel coal onto the table plate and use the jets to blow it to where you want it.

I'll let the old firemen add all the details - my experience of firing with mechanical stokers is limited to a handful of locos of classes 15F, 25NC and GMAM.

[Derek Walker]

Thanks guys, it makes sense, but I am just thinking surely steam jets would be counter productive in a firebox, wouldnt there be a tendency to quench the flames or reduce the heat?

[Mike Haslam]

Derek,

the volume of steam (hot - fed from the boiler) is small compared to the volume of air being drawn into the fire. The jets are very fine and it's the pressure rather than the volume which is doing the job.

My colleagues did not answer a part of your question, John almost did. The reason for the mechanical stoker is that when the locomotive is pulling a heavy load at speed, a normal fireman would not be able to provide the amount of coal needed to generate the steam. The 15F and other locomotive's work often entailed this. Nowadays with restrictions, these lovely machines never really get to their potential.

I was fortunate to train as a fireman in the last days of Spoornet crews and worked on both hand-fired and mechanical stokers. Let me tell you, doing shunting with a mechanical stoker is a bind. Because of the slow speeds, stop and start, I usually found it easier to hand-fire. However, what a difference when doing some real work - a 15 coach train, at speed on a long straight road. The mechanical stoker humming away, smoke just right, fire white and needle up to the mark. The locomotive purrs! And you get a view of the road ahead too instead of being inside shoveling, though it is necessary to check the fire visually from time to time in order to make adjustments to the coal distribution if necessary. But when everything is working well, man! that's a real footplate experience.

On the whole, hand firing has more control, uses less coal (and makes less ash for the fireman to throw out!), but the mechanical, once mastered is also good.