Single Lever Control of Steam Engines e.g. Shovel Engines

Peter Short

Subscriber
In another thread a member asked about the valve gear found on the swing or slew and crowd engines of steam shovels.

The steam engines in question are two cylinder (duplex) type with only one eccentric per cylinder and yet can be started, stopped, reversed and have their speed varied by a single control lever. Very convenient….but how does that work?

These engines are mechanically simple, but wonderfully ingenious designs!

The single eccentric type of reversing gear can be found on winches, steering engines and shovel engines etc., the type of engine where steam is delivered for the full stroke of the piston (no lap or lead on the valves). Thus they are powerful, and are guaranteed to start without hesitation in either direction at any crank position, (when two cylinders are used). “Economy in steam consumption is sacrificed for certainty in working”.

I am guessing they also have a good "power-to-weight" ratio, thus ideal for attaching to the jib of a steam shovel.

Another benefit – the single control lever can be moved to any position and it will stay put, no lock required. The reversing lever on a “normal” steam engine “kicks” and (usually?) needs to be locked to prevent it moving.

These engines were made with slide valves for cylinders and control valve or piston valves for their cylinders and control valve. (And combinations of both)

The question remains – how do they work?

I would not have figured this out without the help of Asquith and the late Robert Grauman. Robert measured up a Vulcan steam shovel and drew it in 3D CAD. He had a keen interest in mechanical design and spent his holidays investigating and measuring up old machinery. He contributed many excellent posts on the Practical Machinist Forum.

Any correction and discussion welcome, I could be wrong about any of it and certainly have only seen a small part of the whole picture. I am sure there will have been variations used.

Looking first at a winch engine with slide valves on the cylinders and control valve.

1 (see 1st photo, fig. 79); first of all, plan view of the winch engine. Two cylinders with their cranks at 90 degrees, single eccentric for each cylinder, single control valve, all slide valves, single lever controlling speed and direction. Eccentrics probably at 90 degrees to crank pins.

2 (2nd photo, fig. 79 detail); detail of the ports in the cylinder block. (I can't figure out what the wall is that seems to separate the RH slide valve from the control valve. As far as I can figure, all the valves are in a common chamber 'E', so the wall has me puzzled).


3 (3rd image, fig. 81 & 82) description of the valve gear, and diagrams showing the clever design of the engine slide valves (fig. 81). They are not like "normal" slide valves at all, but have double porting. The steam in the valve chest no doubt holds all the valves (including the control valve, fig. 82) on their seats at all times, and all the "work" is done inside the engine slide valves, whereas a "normal" (non double-ported) slide valve uses its outside end faces to admit and cut off steam.

Continued in next post.
 

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Peter Short

Subscriber
Re: Single Lever Control of Steam Engines e.g. shovel engines

Continued:

4 (4th image) CAD drawing of winch, with control valve in “full forward" position, and engine slide valves shown for that direction. The slide valves are actually shown fully open (as when the piston is at mid-stroke). I have used the same letters as the diagrams above. Note; I-G-I is a common chamber, so is J-H-J.

5 (5th image) as 4, but with control valve in "full reverse" position. Note how the porting in the engine slide valves has changed.

I will post something about the piston valve type, if there is any interest?
 

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J Dayman

Subscriber
Re: Single Lever Control of Steam Engines e.g. shovel engines

Thanks Peter, I'd be interested to see your piston valve diagrams. You are right, the guys that came up with these valve systems a hundred years ago were very clever!

Best regards Jeff Dayman
 

Peter Short

Subscriber
Here are diagrams and text explaining how a similar "single lever control" winch or capstan engine works with piston valves.

I am not sure how many different designs were used, this one uses hollow piston valves.

Taken from "Naval Marine Engineering Practice", volume 1, 1959.
 

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Peter Short

Subscriber
This is a steering engine using piston valves, single eccentrics, single control valve.

Sorry, no images, I get a message saying I have exceeded my quota. I am not sure what that means.

BTW, the images in post #1 & 4 are taken from Modern Engines and Power Generators volume 5, by Rankin Kennedy, c. 1905-1906.
 

Peter Short

Subscriber
From the last post: This is a steering engine using piston valves, single eccentrics, single control valve.

I was re-reading this thread and realised I didn't get around to posting the photos. Here they are.

Steering engine made by Clarke, Chapman & Co. "a favourite type".

From Slide Valves and Valve Gearing by Peter Youngson, 1919.
 

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terrywerm

New member
Peter, thank you so much for the detailed information you have posted, I believe it will be quite helpful! :salute:

I now only need to figure out how this all worked with rotary sleeves around the piston valves. The photos that Ron posted in my thread should be most helpful in that regard.
 
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