The Soulé Rotary Engine

Gallery opened March 2004

Updated: 3 Mar 2018
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This page devoted to the Soulé rotary steam engine was missed out when the website was transferred from aqpl43 to Apologies for that. Here is the page again, with a new update.

The Soulé Steam Feed Works was established in Meridian, Mississipi in 1891. Its main product was machinery for the lumber business. They made a rotary steam engine known as the Soulé Steam Feed, "Feed" in this case referring to feeding wood into a circular saw on a power-driven carriage. It operated with radial vanes turning in an elliptical chamber. The engines were in operation from 1892 to 1922; a US patent was taken out in 1896, and another in 1902. Some 2300 rotary engines were made and sold all round the world; according to Wikipedia there are still a few working in Australia and India.

Left: The Soulé rotary steam engine, circa 1893; a Series "C" model.

The valve at the top allows steam to be fed into either side of the engine for reversing, via the large vertical pipes. The small vertical pipes, which appear to be fed from before the reversing valve, are for pressurising the centre of the rotor. More on this below.

This engine worked in a factory owned by the inventor for many years, though it is not quite certain that this constitutes an impartial trial. It was also manufactured for sale, though how many were sold is unknown. Feeding wood into a saw requires a limited amount of power, (much less than that required to turn the sawblade) so some inefficiency may have been tolerable. One advantage was rapid reversing, by simply operating a valve.

The internal arrangements are revealed in detail below.

Left: The Soulé rotary engine in steam

This looks very like the engine in the small picture above.

The Soulé works still exists and hosts a Steam Festival every year; a Soulé rotary is on of the exhibits, though it does not appear to be driving anything. The steam escaping from each end may portend the usual rotary sealing problems.

The numbers of the US and Canadian patents are embossed on the side of the engine.

This is one of the three Soulé rotary steam engines known to survive.

I present here, through the kindness of Henry Taves, a unique view inside a surviving rotary steam engine. This is a less powerful model than that pictured above; the central part of the housing is noticeably less wide (6 inches) but the other dimensions appear to be the same. Clearly the end-housings were standard, and central sections of different width were mounted between them to get different power outputs.

It appears however that Soulé, like everyone else, discovered that rotary steam engines have low efficiency, too low even for duties such as saw-mill feeding. The company therefore switched from making the rotary engine to the "Spee-D-Twin", a conventional design with two horizontal reciprocating cylinders, which was more efficient and also quick-reversing. The Soulé factory was able to produce one Spee-D-Twin steam engine per day when in full production; and it sold worldwide from 1901 until as late as 1996, a total of 4,301 units being built. The museum owns the last Spee-D-Twin engine built, No 4031; steam engine number 4300 was sold 1996 to James M. Wills of Perkinston, Miss.

All the photographs below are most kindly provided by by Henry V. Taves.
The engine itself is the property of The Southern Forest Heritage Museum at Long Leaf, LA. The engine was found in the ruins of the Finished Lumber Shed of the Museum, which was previously the Crowell Long Leaf Lumber Co.

Restoration is being undertaken by David Hamilton.

There are only three known examples of the Soulé engine; the other two are in Mississippi. The Soulé factory itself has also been preserved as a museum. See

Left: The Soulé engine. The central section is on left, and an end housing on the right.

Henry Taves informs me that the inside of the engine shows very little wear, and it therefore appears to have seen little use.

The feet for mounting the engine are cast integrally with the end housings.

Left: The Soulé engine. The rotor with its radial sliding vanes.

It appears that the vanes were pressed against the inside of the casing by supplying steam pressure to the centre of the rotor. Note the curved packing pieces between the vanes, on the side face of the rotor; presumably these helped to maintain a pressure differential.

Left: The Soulé engine. The exterior of the end housing.

Steam ducts are cast on the outside of the end housing.

Left: The Soulé engine. Rotor and central section.

Note the substantial output shaft, which appears to be designed to transmit some serious power. The power output of this engine is unknown.

Left: The Soulé engine. There are eight radial slots for the vanes in the rotor.

The central housing section on the left bears the words: "SOULE STEAM FEED"

Left: The Soulé engine. End view of rotor with vanes removed.

The semi-circular cutouts in the rotor at first appear to be solely to reduce weight, but they may have had a role in allowing steam to get behind the curved packing pieces.
Note the keyway in the end of the output shaft.

Left: The Soulé engine. The 41 moving parts in the rotor assembly.

There are 8 radial vanes, 16 curved packing pieces, and 16 of the little rods, whose function is a little obscure. Add 1 moving rotor, and you get 41 moving parts.

Left: The Soulé engine. The rods were mounted in channels as shown.

The function of these rods is not very clear. They may have been intended to exert pressure on the curved packing pieces, pressing against the walls of the end housings, or may have had something to do with sealing the radial vanes.

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