Rotary Steam Engines: Page 7.

Updated: 28 Oct 2007
La France material added
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THE NICHE MARKET: FIRE ENGINES.
THE SILSBY ENGINE
From what has been said before, it would be natural to conclude that rotary steam engines never did a useful turn of work in their history. You would be quite wrong.

The rotary steam engine found a niche driving rotary water pumps on early steam fire engines. Such engines were made by Silsby and also Ahrens. These engines were horse-drawn; steam only powered the pump.

Why did it succeed here, and here alone?
The rotary steam engine type used was light, compact, simple and reliable.
A short working life was no drawback- a fire engine spent a very small proportion of its life actually pumping. (In 1937 consultant engineer W E Millington stated that the running time of a London fire engine pump was 5 weeks in a total working life of 15 years)
The high steam consumption was of little interest- the cost of coal must have been a miniscule proportion of the cost of maintaining a fire brigade and turning out to a fire. It is significant that none of the many photos of old steamers show any lagging on the boiler or steam pipes. It was accepted that fire engine boilers had to be driven very hard, with a lot of priming, and that they needed the continuous attention of a skilled and experienced man.

Another possible reason is that if the gear-type rotary engine worked non-expansively- which it certainly appears to do- then there would have been a lot of energy left in the exhaust steam. The exhaust was directed to a blast-pipe in the chimney (just as in a steam loco) to increase the draught. Given the emphasis on raising steam in the shortest possible time, a powerful blast might well have been more important than economy. This notion is backed up by contemporary pictures of steam fire engines in use, with smoke rushing vertically out of the chimney.

he internals of the Silsby rotary steam engine
Left: The internals of the Silsby rotary steam engine.

The engine and pump were invented by Mr Birdsall Holly. The resemblance to the Pappenheim/Murdoch type of engine is obvious.
The two rotating elements were known as "revolvers". The packing consists of blocks of metal pressed outwards by springs. No expansive use of steam is apparent.

The internals of the Silsby water-pump
Left: The internals of the Silsby water-pump. Very similar indeed to the engine.

The engine and pump were claimed in the same patent by Birdsall Holly.

The Silsby rotary engine coupled to the water-pump
Left: Top, or possibly side, view of the Silsby rotary engine coupled to the water-pump.

It is not even easy to work out which is engine and which is pump from this contemporary engraving. I think the the engine is on the right, because the pipe fitting looks too small for the water pump.

A Silsby rotary-engine steamer
Left: A Silsby rotary-engine steamer, circa 1885.

Today we have naming of parts. The rotary engine is so compact it is barely visible.

Silsby rotary steam fire-engines were first manufactured in 1856. The rotary pump had been patented the year before by employee Birdsall Holly.

Silsby steamers were highly successful- Silsby was the only firm that built more than 1000 engines. In 1892 the company was merged into the American Fire Engine Company.

The rotary water pump was probably a good deal more efficient than the rotary engine that drove it, because the sealing problem is much easier when you are dealing with a viscous fluid like water.

The reign of the rotary steam pump was relatively short. By the late 1800s it had been displaced by the centrifugal pump which required high rotational speeds.

THE LA FRANCE ENGINE
Another fire-engine manufacturer that used rotary engines was La France. This is an extract from an article in Time magazine:

"Business was slow the last year of the Civil War but Truckson La France of Elmira, N. Y. had an idea. He put on his best bowler and went to call on the rich Diven family. "I've perfected a rotary fire engine," he announced. "I want money to make it with." With a snort Old Man Diven gave him the money. Inventor La France made his first fire engine in an old brick house, sold it to Elmira. It was enough to scare the horses, but it had two lines of hose and only one weakness. The cams on the pumps wore down, refused to deliver the pressure. Firemen fixed that by pouring molasses over the cams. For years a jug of molasses was regular equipment on the old "La France."

From Time for Monday, Nov 26, 1934.
I do not know for sure, but from the reference to "cams" in the article above, it seems likely that the La France rotary was a Murdoch/Pappeneim-type like the Silsby engine. As for use of molasses as a sealant, I'm not sure if I believe that or not. But it does emphasise one of the many drawbacks of rotary steam engines- their tendency to wear rapidly to the point where operation was seriously affected.

The Centennial monorail was powered by what was described as a "rotary steam engine of the La France type".

The La France company still exists: see www.americanlafrance.com.

The story of the Rotary Steam Engine continues on Page 8 of this gallery.

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