Rotary Steam Engines: Page 6.

Updated: 23 Apr 2009
Kemp & Keats Engines added
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A COMPOUND ROTARY ENGINE: 18??

A rare photo of a compound rotary engine
Left: A rare photo of a compound rotary engine.

I have to confess that I have lost my notes relating to this photo. I know it came from the web, and I have a vague recollection it was in an American museum. If anyone can identify it or feels I have infringed their copyright, then please get in touch.


THE DOLGOROUKI ENGINE: 1882

Left: The Dolgorouki rotary engine.

Since I found an actual example in Vienna, the Dolgorouki engine now has its own page.


THE HODSON ROTARY ENGINE: 1882

Left: The Hodson rotary engine.

The French journal Nature (1882/2) described this machine as a "Moteur Rotatif de Grande Vitesse" It was stated that the engine could run effectively between 25 and 2000 rpm.

It was noted by Nature that rotary steam engines, having been generally rejected at an earlier date due to their inefficiency, were now being given a second chance because of the desirability of driving electrical generators directly and at high speed. As we now know, they still failed to find a long-term niche, not least because the advent of the steam turbine was very close.
At the Exhibition of Electricity at the Crystal Palace in London, they reported that the Hodson engine was seen driving generators by Brush, Gramme, and Siemens.

Even at this late date rotary engines were still being designed with rotors that smacked into hinged abutments as they whizzed round. This would seem to be particularly inappropriate for a high-speed machine, and it would be interesting to know how long part A would last at 2000 rpm.
Note also the line-contact between A and rotor B, which made any hope of proper sealing futile...

From the French journal Nature 1882/2

Left: The Hodson rotary engine.

The Hodson engine would not have given anything like a uniform torque, and is therefore fitted with a sizable flywheel. Note the fly-ball governor and the lubricator on top of the cylinder.

From the French journal Nature 1882/2


THE BROWN ROTARY EXPANSIVE ENGINE: 1891

Left: The Brown Rotary Expansive Engine: 1891

This engine was put forward by Alexander Francis Gordon Brown of Swindigemuir, Ayrshire. It appeared in the journal Industries, and uniquely, full details of trials run on it were given. The engine was run at between 560 and 600rpm and yielded between 19 and 22 BHP. The engine was built by Messr John Lang & Sons of Johnstone, ansd it was at their works that the trials were conducted.

The trials were conducted by Professor Jamieson of the Glasgow and West of Scotland Technical College. He said: " ..the gross consumption of steam is only 27.2 lb per IHP-hour, results which surpass not only any other rotary engine, but equal those of the very best simple expansion, fast speed, no-condensing engines with which I am acquainted or have seen recorded." This seems like a pretty good report; perhaps it was lack of durability that doomed the Brown engine, for so far as is currently known it was never heard of again.

From Industries 17 July 1891, p65

Unfortunately what was not given were any clear details of the internals. We are told that the cylinder was 10.5in diameter with a length of 8.625in, but such laudable precision tells us nothing about how it worked. We learn that there were "two oscillating valve doors... ...form part of the working surface of the cylinder when they are closed" which suggests an engine something like The Chapman Engine of 1810. It also suggests an engine that would not keep working very long, but the Brown engine ran for a good five hours during the trials, so perhaps its construction was different.

The steam supply came in through the bifurcated pipe at the top, and was admitted by rotary valves on each side, driven by the gearwheels seen in front of the engine. The cut-off could be adjusted manually or automatically by a governor.

Left: The Brown Rotary Expansive Engine patent: 1892

A F G Brown took out three US patents for rotary steam engines; No 420,331 in January 1890, No 478,843 in July 1892, and No 507,780 in October 1893. The engine illustrated above is believed to use the 1892 design shown here. The 1892 design was patented in England in 1889 as No 16,913.

Once more there are unsealable line contacts and big bits of metal banging about, which is hard to reconcile with Professor Jamieson's positive report.

From US patent 478,843 12 July 1892


THE BEHRENS ENGINE: 1886

Left: The Behrens rotary engine: the exterior.

This engine was introduced by Henry J Behrens, and patented in the USA in 1866. It also has a hefty flywheel. As with the Hodson engine, there is a fly-ball governor on top of the casing, which controls the steam coming in via the vertical pipe at top left.

There are three conical-shaped things fitted with valves. I am not sure, but they are probably lubricators. The rotor synchronising gears can be seen between the governor drive-belt and the flywheel.

Deschanel remarks, (on rotary steam engines in general) "Hitherto... the results obtained by this method have not been encouraging." However, he describes the Behrens engine as "one of the best examples."

From Elementary Treatise on Natural Philosophy by Deschanel, trans J D Everett. Pub 1886 by Blackie & Son. Vol 2, p505

Left: The Behrens rotary engine: the internals.

The two C-shaped bits marked c, c' stay still while the scimitar-shaped rotors go round in opposite directions, synchronised by gears outside the casing.

B is the steam admission pipe, while the exhaust is at D.

The Behrens engine has the advantage that it avoids line-contacts between rotor and casing that would make proper sealing virtually impossible. It looks like one of the more promising engine geometries.

From Elementary Treatise on Natural Philosophy by Deschanel, trans J D Everett. Pub 1886 by Blackie & Son. Vol 2, p506
This drawing is clearly derived directly from the patent drawing below.

Left: The Behrens rotary engine: animated.

Bill Todd points out that this raises the question: how do the two rotors connect to the output shafts? See below...

Another superb animation by Bill Todd, who is unquestionably the leading rotary-steam-engine animator in the world.

Left: The Behrens rotary engine: one of the rotors. (speculative)

How do the two C-shaped rotors connect to the output shafts?

Bill says: "As far as I can see, the only way would be to add a disk to the end of each rotor (see drawing) then recess these disks, one into the front cover and one into the back cover, so the opposing rotors could sweep across the disks, flush with inside of the cylinder."

Sounds good to me.

Drawing by Bill Todd.

Left: The Behrens rotary engine: exploded view

Note the addition of balance weights to the rear of each rotor disc.

Drawing by Bill Todd.

Left: The Behrens rotary engine: patent drawing

Fig 1 from US Patent No 53,915 dated 10th April 1866.

Left: The Behrens rotary engine: patent drawing

Plan view showing the synchronising gears and balance weights on the back of the rotor discs.

Fig 2 from US Patent No 53,915 dated 10th April 1866.

Left: The Behrens rotary engine: patent drawing

Variation on a theme; Mr Behrens claims that the engine is balance by having two "pistons", and that "one upon each shaft is acted upon during one-fourth part of a revolution". He is presumably referring to the dynamical balance of each shaft; a symmetrical arrangement as shown here would remove the need for balance weights on the rotors.

Fig 3 from US Patent No 53,915 dated 10th April 1866.

Development of the Behrens engine was clearly continuing in 1868, for in that year another US patent (No 77,373 dated 28th April 1868) showing an engine very similar to that in the first patent, was taken out by a Dexter D Hardy, and assigned to Behrens.


SUCCESS AT LAST? THE HULT ROTARY ENGINE: 1889

The Hult engine coupled to a blower
Left: A rare thing; a picture of a rotary engine coupled to a load and apparently ready to do a job of work. This is the Hult engine.

This engine was built by the Hult Brothers Rotary Steam Engine Company of Stockholm, Sweden, and was described in American Machinist for May 1902, the claim being made that there was at least one successful rotary design in the world. It was stated that the Hult was "in extensive use for all purposes" such as driving dynamos and centrifugal pumps, in Sweden, and that it was used for driving lighting generators in both the Russian and Swedish navies.

A 30 horsepower engine was 50 x 25 x 20 inches, and ran at 750 rpm, though speed was 500 - 1500 rpm across the range of models. Steam usage was quoted as 39 pounds/BHP-hour non-condensing, and 29 pounds/BHP-hour condensing.

Transverse and longitudinal sections of the Hult engine

Above: Transverse and longitudinal sections of the Hult engine. This is a two-cylinder version; cylinders at R and S.

Modus operandi: the two cylinders R and S are fed steam alternately to aid constancy of torque. The cylinder turns as well as the pistons ("piston" derived as we have seen from "pestle" is a quite inappropriate word to use for a structure that rotates) in order to eliminate motion at the sliding contact between them. This line of contact is always at the top.

Steam enters at the right, and passes down the hollow central shaft, which has admission ports cut in it. These feed steam through the straight passages in the piston to the two working volumes 3 and 2 at appropriate times, and force is exerted on the spring-loaded shutter sticking out of the cylinder. The exhaust passages are the curved ones.

Admission cutoff is varied by rotating the inner steam-distribution tube by means of the small handle at the end. Reversing is effected by swopping admission and exhaust ports; the large lever does this by sliding the rotating tube 1.

End sealing: the two plates between cylinders R and S are forced apart by wedges pushed inwards by adjusting screws, (accessible via plug G) and this suggests that continual adjustment to take up wear may have been necessary to control leakage. This is not encouraging; piston engines do not require regular adjustments to their piston rings, and here we get a clue as to one of the problems of the rotary engine- its geometry is an inherent weakness, because you would have to take up wear in several directions at once.

The Hult is claimed to allow the expansive use of steam, but the very narrow exhaust ports seem to make this difficult.

More sections of the Hult engine

Above: More sections of the Hult engine.

There were five sets of roller bearings in the engine, disposed thus:

Section A-B Support bearing for central shaft combined with a friction-drive epicyclic speed reduction gear. Friction? How did you keep the oil away?

Section E-F Two cylinder bearings, each with eleven rollers. One fitted at each end of the central cylinder.

Section C-D Two piston bearings.

Marine version of the Hult rotary engine
Left: Marine version of the Hult rotary engine.

The big lever gave control of forward, stop, and reverse.

This engine gave 45 bhp at 10 atm steam pressure.

A 200 bhp version was 6ft long by 4ft high by 3ft wide.

Steam consumption was 30 to 45 lb/hp, depending on steam pressure.

From the Model Engineer and Electrician, 28 May 1903:
"A new type of rotary engine, constructed by the Hult Brothers Rotary Stean Engine Company, of Stockholm, is being introduced into the country. We understand that one of these engines may now be seen running, at noon any day for a few weeks at the works of Messrs Simpson and Co, 101 Grosvenor Road, Pimlico."
No further reference to this enterprise in England has so far turned up.

Felix Wankel says:
"Only transitory successes have become known. The first partially successful example recalls the steam engine designed in 1899 by O W Hult in Stockholm and manufactured in Germany by the Kieler Maschinenbau A G , who produced various sizes of engines which developed 35 - 113 BHP. The aggregate power of the engines built amounted to about 6000 BHP." So if all the engines were of the smallest size, 171 were built. If al of the largest, 53, so the actual number presumably lies somewhere between the two...


THE FILTZ ENGINE: 1897

According to Nature, this engine was invented some years before its publication in 1897. It also said that a "fairly large number" had been constructed and put into use.

Left: The Filtz compound rotary engine; 1897.

A single-cylinder version of the engine weighed 28 kg and developed 5 HP at 1200 rpm; steam pressure was described as 6 kg, presumably meaning 6 kg/cm2 which is 85 psi. The "diameter" was given as 94 mm; presumably this was the diameter of the internal rotor as it seems too small for an outside dimension.

The compound version shown here, running at the same inlet pressure with 350 and 600 mm diameter cylinders, was stated to give 40 HP at 300 rpm, using 9 to 10 kg of steam per horse-power when working with a condenser. It had a volume of less than one cubic metre and weighed 1200 kg, presumably without the condenser. (That's over a ton, and seems very heavy for a 40 HP engine) In the compound design, the two rotor assemblies were staggered in angular alignment to smooth out the torque delivery.

A version with a nominal output of 70 hp was said to actually be capable of 100 hp.

From the French journal Nature 1897/1

Left: The Filtz compound rotary engine; 1897.

Tht operation of this engine is not very clear from the text and drawings, but it goes something like this:

The engine shaft M carries two rotors which have faces in the form of helicoidal ramps. They are divided from each other by the fixed partition P. Two vanes A and B slide in and out through P as the helicoidal ramps turn with the shaft, forming steam spaces that expand and contract. Steam moves in and out of these spaces through ports in the helicoidal faces, exerting pressure of which one component is in the direction to cause rotation.

From the French journal Nature 1897/1

This construction, with the sliding vanes bearing against a ramp of constant slope, would seem to offer at least the possibility of an area seal against the ramp rather than a line contact.

Left: The Filtz compound rotary engine animated.

This animation by Bill Todd is based on the 1896 patent.

Bill says:
"The outer part of the rotor has been removed and the front ramp is transparent to show the internals better. The input and exhaust chambers are the two semi-circular cut-outs in the ramps. The brass bit at 12o'clock is a seal to stop leakage directly between inlet and exhaust ports. I've angled the edges of the blades as Filtz's square edge blades would have jammed; the varying angle between blade and ramp means only a line contact is possible. (Filtz's blades were two parts, sprung apart to 'seal' against the ramps)

Another brilliant animation by Bill Todd

The steam expansion ratio was calculated by M R Guyoot-Sionnest, the naval construction engineer to be 1.5, which persumably means admission cutoff at 66%. Nature pointed out "this corresponds to a mediocre utilisation of the steam"

M Filtz appears to have then turned his attention to petrol engines, for it is recorded here (external link) that a pre-WW1 aeroplane called the "Bonnet-Labranche No.2" designed by the brothers Emile and Albert Bonnet, was powered by a 30 hp Filtz-Arion engine.


THE UNBEHEND ENGINE: 1898

Left: The Unbehend rotary engine; 1898.

This rotary engine was patented by Mr Jacob J Unbehend in June 1898; he was awarded US patent No 606,606.

The engine has a central rotor B from which protrude gear teeth; these are morticed in place in the rotor to allow ease of replacement. On each side of it are rotary admission valves C which are synchronised with the main rotor by external spur gears. Steam enters through the centre of these valves and passes into the working chamber through their radial passages, and pushes round the main rotor, both at top and bottom to "maintain equilibrium" and presumably cancel out side-thrust on the main rotor bearings. Exhaust was via passages f and valves g. The position of these valves, and the operation of the admission valves, could be changed by a single lever to reverse the engine.

There seems little scope for the expansive use of steam, and there are no means shown for sealing the tips of the gear-teeth to the inside of the casing. The patent drawings have a practical look about them which suggests that this engine might have been actually built.


THE TAYLOR ENGINE: 1899

Left: The Taylor rotary engine; 1899.

This rotary engine was patented by Mr C G Taylor of Kansas, USA. It is of the sliding-door type. The spring-loaded door seen at the centre of drawing 2, with its little ant-friction roller, is supposed to be pushed out of the way of the spring-loaded vane carried on the rotor by a cam on said rotor. This will bring in the usual problems of door timing and leakage.

Steam admission was controlled by rotary valves operated by a small eccentric, as seen in drawing 1. Speed could (in theory, at least) be controlled by varying the cut-off; the thin vertical rod in drawing 1 connected to a governor. The small lever apparently reversed the engine by interchanging the inlet and exhaust functions.

From the size of the pipework, it can be deduced that two outer chambers in the valve chest were for inlet, and the central chamber was the exhaust passage. The large central valve appears to allow exhaust to be taken from either side for reversing. However the arrangement of the inlet valves is a bit mysterious- there seem to be two in parallel on each side; I suspect the drawing may be wrong.

From The English Mechanic and World of Science, 6 Jan 1899, p486.

Left: Side view of the Taylor rotary engine.

The engine consisted of two rotors, presumably to reduce torque variations during a rotation.

The cams that operate the vertical sliding-doors can be seen just inside the casing at the ends of the double rotor structure. On the left rotor the vane is at the bottom and the vertical door is closed; at right the vane is at the top and the door has been lifted to let it pass. No division between the rotor compartments is shown, which must be wrong.

From The English Mechanic and World of Science, 6 Jan 1899, p486.

Left: The Taylor rotary engine; 1899.

Description from The English Mechanic and World of Science for 6 Jan 1899, p486.

It is impossible to believe that this engine could ever have worked satisfactorily.


THE HAY & DEPUY ENGINE: 1899

Left: The Hay and Depuy rotary engine; 1899.

James T Hay and Gilbert L Depuy came from Garland, Texas. The operation of their engine is fairly clear from the diagram; there are two vanes that slide in and out under the control of cam grooves in the end of the cylinder; it is not easy to see here but there are swivelling shoes on the ends of the vanes. Steam is admitted via ports in the rotary valve shown in the centre of the picture; how it gets out again is not clear, but the large vertical pipe shown on the right is presumably for the exhaust.

From The English Mechanic and World of Science, Sept 23 1899. The original report appears to have come from Scientific American

The lever-operated slide-valve arrangement on top of the cylinder is for reversing. The brief article describing the engine makes some interesting remarks on the sealing problem: "In order to prevent leakage of steam, the inner faces of the cylinder-heads, the interior of the cut-off valve casing, and the cut-off valve, are formed with grooves adapted to receive the water of condensation. As they fill with water, they form a packing for preventing the escape of steam."

I really have no idea whether that would work or not, but I suspect not.


THE TOENNES ENGINE: 1899

Left: The Toennes rotary engine; 1899.

Patented by Richard Toennes of Boonville, Missouri, this engine was designed to use steam expansively. The rotor was mounted eccentrically and the spring loaded vane had a rocking shoe on the rubbing end. There were two ports, used interchangeably for inlet and exhaust, the direction of rotation being selected by the reversing valve plate at 3 in the picture. This plate was shifted by the lever shown at 1. The main valve plate was moved back and forth by an eccentric on the main shaft. Steam could be cut off at 1/4, 1/2, or 3/4 of the piston 'stroke'. Lubrication was fed in at three places only.

Fig 1 shows the engine partly cut away to display the cutoff mechanism. Fig 2 is a section, and Fig 3 shows the reversing valve plate.

From The English Mechanic and World of Science, Oct 13 1899.


THE JAMES ENGINE: 1900

Left: The James rotary engine: 1900.

This engine was patented by William James of Phoenix, Arizona. According to the full text below, it is a rare example of a compound rotary engine, but this is contradicted by the picture here which shows two engines of identical size connected to the same steam supply coming in from the top. The text states that two engines were connected together out-of-phase to avoid dead-centre problems.

There is no full drawing of the internals, but the details in Figs 2 and 3 make it clear that a cylindrical rotor inside a cylindrical casing carried a small ramp which knocked aside a swinging door A as it passed. B is a dash-pot composed of a plug moving in and out of a hole which was intended to reduce the violent shocks on the door when it swung in to contact the rotor.

D is a rotary admission valve driven by gearing, intended to give expansive working; no sealing details are visible. Steam reached the rotor via a narrow port running through the swinging door, but confusingly this is drawn differently in Figs 2 and 3; Fig 2 is probably the correct arrangement.

From The English Mechanic and World of Science, Jan 12 1900, p489.

The exhaust arrangements are not shown; presumably the joined pipes emerging from the lower parts of the valve chests carry away the exhaust steam, which goes off to the left. The exhaust piping is not much bigger in diameter than the inlet piping, so one wonders just how much expansion was going on. Note the two little drainage cocks at the bottom of the valve chests.

Left: The James rotary engine: 1900.

The text of the article in The English Mechanic.

What immediately stands out with this engine (apart from the usual impractibility of having swing doors or abutments banging about inside it) is the very small area of the ramp face on which the steam pressure acts. Almost all the volume of the engine does nothing at all; even if everything else worked the power-to-weight ratio would have been laughable. This is a common characteristic of swing-door and revolving-door engines, such as The Eve Engine (1825), but this is the worst example discovered so far.

It is not currently known if this engine was actually built and tested.

From The English Mechanic and World of Science, Jan 12 1900, p489.


THE CROSTON ENGINE: 1901

Left: The Croston rotary steam engine; cross-section: 1903

Thomas Croston took out US patent No 674,258 in May 1901. It was for a very complex system that actually consisted of two engines- a main rotary engine and an auxiliary governing engine; speed was controlled by varying the admission cut-off.

The picture here shows a transverse section of the main engine. E and E'are the rotary inlet valves; the angular relation between them was altered by the governor to control the admission period. When cut-off valve E' lagged behind valve E it admitted steam for a longer period.

Note that the spring-loaded vanes are also pressed outwards by small steam cylinders C3 and C'3; each has a pair of valves connected by a see-saw lever, that ensure that the side of the vane at the highest steam pressure is connected to the cylinder. A seal B presses against the top of the rotor.

The rotary exhaust valves are at J and J', and steam leaves through the port at the bottom the casing. The narrow and winding steam passages do not look as though they would encourage steam flow.


THE KEMP ENGINE: 1901

Left: The Kemp rotary steam engine.

Thomas Kemp of Bath puts forward a design that is at least different. A piston is working in a cylinder in the usual way, but according to the patent "there is a spiral groove in the middle of the piston". Spiral doesn't seem to be the right word as the piston would screw itself to the end of the cylinder and stay there; in fact from the drawing the groove appears to be continuous so the piston could rotate continuously as it went to and fro. The expansive use of steam appears to be possible with suitable valve-timing, and and the usual sealing difficulties are not present as the piston is sealed with conventional piston rings at each end.

This info is extracted from UK patent specification, No 26,452. (1901)


THE BRIDGE ENGINE: 1903

Left: The Bridge rotary steam engine; cross-section: 1903

Homer E Bridge received US patent No 735,203 in August 1903. A small circular piston D went round inside an annular space a, in an anti-clockwise direction as shown by arrow x. The small rotor E kept the inlet and exhaust sides of the piston sealed from each other,and also acted as a rotary valve; it was driven by a notched wheel which was intermittently pushed round by a pin on a disc that was coaxial with the main rotor.

The handle F3 appears to have varied the cut-off. Another handle attached to the valve K allowed starting, stopping, and reversing by rearranging the steam passages to the small rotor.

Like the The James Engine above, it is noticeable that the piston area is very small compared with the size of the engine, and even if everything else had worked, the power-to-weight ratio would have been poor. There are however, the usual sealing problems, such as the line contact between the two rotors.


THE COOLEY ENGINE: 1903

Left: The Cooley rotary steam engine; cross-section. American, 1903

The Cooley engine has a two-lobed inner epitrochoid working in a three-lobed outer envelope; both rotate in the same direction and are geared together in the ratio 3:2. The simplified drawing to the left is clearly taken from the last Cooley patent, No. 748348.
This design is interesting because its eccentric rotor with internal gearing clearly foreshadows the Wankel engine. It is not clear from this diagram how steam enters and leaves, but the inlet and outlet ports can be seen in the second Cooley patent drawing below. This is a distinctly more sophisticated concept than most of its predecessores, but there are still line seals and the end sealing to grapple with.

In 1908 the English engineer Umpleby tried to make an internal combustion version of this design, but did not get far with it. See The Umpleby Engine.

A point of note is that the inventor, John F Cooley of Suffolk county, Massachusetts, was a pupil of Reuleaux, and was hired to work on rotary piston engines in Berlin under his direction. This is interesting in the light of the very low opinion Reuleaux had of rotary engines. (NB: This info comes from Norbye and has not been confirmed so far)

Left: Animation of the Cooley rotary steam engine.

Here it can be seen clearly that the inner rotor rotates about its center, but the outer envelope is mounted eccentrically.

This superb animation is kindly provided by Bill Todd

Left: Engine drawing from Cooley's first patent, No 724665 of 1903.

The design was covered by US patents 724,665, 724994, 725615, and 748,348, which are shown here. All these patents were in 1903, the last being dated 29 Dec 1903. As with many rotary engines, it was also patented as a pump. There was a British patent 6168 (1903); this is such a low number I assume the British patent numbering system must have been re-organised not long before.

Left: Engine drawing from Cooley's second patent, No 724994 of 1903.

The top half of the drawing shows the somewhat labyrinthine ports by which steam or some other fluid de jour entered and left the working chambers.

Left: Engine drawing from Cooley's third patent, No 725615 of 1903.

Left: Engine drawing from Cooley's fourth patent, No 748348 of 1903.

Two companies were set up to exploit this engine; the Cooley Epicycloidal Engine Development Company of Boston and of New Jersey, and the Cooley Epicycloidal Engine Company. (incorporated in New Jersey)

Left: Newspaper announcement of the formation of the Cooley Epicycloidal Engine Company.

This appeared in the New York Times on Friday, March 20, 1903.

Cooley was originally an electrician born in Penn Yan; he married in El Mira. He was also the originator of the Cooley Airship project, (external link) which appears to have come to grief in a rather dubious manner.

John F Cooley should not be confused with Mortimer Cooley, who taught steam engineering at the University of Michigan from 1881 to 1927.

Many thanks to Jack Cooley Clifford (grandson of John F Cooley) for the above biographical information.

Additional info from the book The Wankel Engine: Design, Development, Applications by Jan P Norbye


THE PALINDROME ENGINE: 1906

Left: The Palindrome compound rotary steam engine.

The operation of the Palindrome engine is rather enigmatic, as no diagram of the internals was published in my source, but there was a lengthy description in the text. There was a rotary piston and a rotary valve, coupled with spur gearing to rotate in opposite directions at the same speed. The piston had a flat vane, and the valve a hollow cylinder, rotating on a fixed tube through which the steam entered. There does not appear to be a major breakthrough in technology here.

It is not quite clear what the picture represents- it looks more like two identical engines coupled together rather than a compound engine, which would presumably have one rotor casing obviously bigger than the other. The larger bottom part of the casing no doubt contains the rotor, and the smaller section above it the rotary valve. There is another even smaller housing above that, which may or may not be interconnected with the reversing lever- possibly it contained a stop valve.

Why 'Palindrome'? Well, a palindrome is a word or phrase that reads the same in either direction. This is presumably a reference to the fact that the engine was reversible, though this was by no means the first reversible rotary steam engine.

From the article: "Great things are expected from the engine by the inventors, and a syndicate is, we understand, being formed for the purpose of exploiting the invention."

The inventor, or at least one of them, appears to have been a Mr Bruce.
"Mr Bruce will be pleased to show these engines under steam to any reader by appointment at Miller's Wharf, Lower East Smithfield, London East. (near Tower Bridge)" Not for the first time, Tower Bridge is associated with rotary steam engines. See
The Tower Engine. These are deep waters, Watson.

From Model Engineer and Electrician, 1906


THE ELLIS ENGINE: 1906

Left: The Ellis rotary steam engine.

The Ellis engine is of the common eccentric-rotor moving-vane type. Its only real point of interest is that it originated from New Zealand. This info is extracted from the patent specification, No 21409.

Apologies for truly dire image quality.

Source unknown #6


THE KEATS ENGINE: 1909

Left: The Keats rotary steam engine.

Robert Keats of Portsmouth puts forward another version of Pappenheim's cogs. The restricted passages for steam entry and exit look rather dubious, but that would be the least of the problems, which include no expansive use of steam and the usual sealing difficulties.

This info is extracted from UK patent specification, No 25,388. (1909)


THE MCEWAN ROSS "ROTA" ENGINE: 1912

Left: The McEwan Ross "Rota" rotary steam engine.

Some further details on this machine have recently been uncovered.
Firstly, I have for some time described this as the "McEwan & Ross" engine, but it appears that Mr McEwan Ross was just one person.

Secondly, the internal arrangements are now known in detail. See below:

From The Book of Modern Engines by Rankin Kennedy. Volume 2, p19. Pub Caxton Publishing Company, London, in 1912.
Left: Section of the McEwan Ross "Rota" engine.

The eccentric shaft e-e rotates around the central shaft b-b, carrying around the four cross-arms. The four pistons move up and down these arms, inside the eccentric cylinder d. This causes the spaces between the pistons to expand and contract, and filling and emptying these volumes with steam generates rotation. Cylinder d rotates with the pistons, minimising their relative velocity.

Now this looks a bit more like it. There appear to be no line contacts which make sealing virtually impossible, but instead broad areas at the outside ends of the piston which could be effectively sealed with something like piston rings. Also, the rotating cylinder should reduce friction and wear.

From The Book of Modern Engines by Rankin Kennedy. Volume 2, p19. Pub Caxton Publishing Company, London, in 1912.
Left: Side section of the McEwan Ross engine.

Steam enters via the hollow support column on the left, and leaves via the column on the right.

From The Book of Modern Engines by Rankin Kennedy. Volume 2, p19. Pub Caxton Publishing Company, London, in 1912.
Left: Animation of the McEwan Ross engine.

This shows how the volumes between the pistons expand and contract due to the eccentric mounting of the shaft carrying the cross-arms.

This most excellent animation is kindly provided by Bill Todd.


THE BROWN ENGINE: 1912

The Brown design is described in a book dated 1912 as "the last and best attempt on a practical scale". It certainly wasn't the last rotary steam engine, but this does seem to suggest that it enjoyed some success. However, this is contradicted by a statement at the end of the description saying "...the number of reciprocating parts is great, and it did not come into practical use".

Note that the cylinder is mostly surrounded by incoming steam and is thus steam-jacketed. Steam-jacketing improves efficiency with normal steam engines by reducing condensation, but I think that would be the least of your problems here.

Left: The Brown rotary steam engine; cross-section.

Naming of parts:
C cylinder
ED exhaust door
EP exhaust port
P piston
PS packing springs
S output shaft
SP steam port
SV steam valve (admission)
VS valve shaft (admission)
SS spiral springs

From The Book of Modern Engines by Rankin Kennedy. Volume 2, p16. Pub Caxton Publishing Company, London, in 1912.
Left: The Brown rotary steam engine; section in plan. This diagram gives a better view of the sealing arrangements.

How it works:

The steam is admitted by rotation of the left steam-valve SV.
The piston rotates under this pressure, the steam from the previous admission leaving via the right exhaust-port EP, while the right exhaust-door ED maintains the sealing (?) of the piston.
On the second half of the piston's revolution, the same actions occur with the right-hand steam-valve SV, and the left exhaust door and exhaust ports.

This seems very unpromising to me, with all those heavy doors banging in and out; it's not exactly free of reciprocating parts, as noted at the time. It also looks as if it would be impossible to reverse it, as the rotor seal would catch on the noses of the exhaust doors.

A one-door version of the engine could also be built.

From The Book of Modern Engines by Rankin Kennedy. Volume 2, p16. Pub Caxton Publishing Company, London, in 1912.

Left: The Brown rotary steam engine animated.

Bill Todd tells me that the exhaust doors "accelerate like mad, even though Brown has attempted to use a smooth cam profile. They are effectively controlled by the edge seal as it sweeps within millimetres of the door's pivot." This would presumably add to the wear on the seal, if it has to provide the forces to waggle the heavy doors back and forth at speed.

This most excellent animation is kindly provided by Bill Todd.

It is an interesting question if this Brown is the same man as A F G Brown, who produced the engine earlier in this page in 1891. Currently I don't know.


THE MARKS ENGINE: 1912

Left: The Marks rotary steam engine; cross-section.

A is the main rotor, with two vanes, and B and C are auxiliary rotors that rotate at the same speed, synchronised by external gearing, and having cutouts into which the vanes of A fitted. On the outside of B and C are two narrow channels in which steam presses these rotors inward to avoid sliding friction, and indeed the inventor claimed that there was no metal-to-metal contact inside the whole engine. If this was true it was a remarkable achievement. A small experimental engine delivered 10 HP with 80 psi steam, running at "well over 4000 rpm, and maintaining this speed without noticeable heating." a reference to the high frictional losses in the average rotary steam engine if it was packed to be steam-tight.

D, E,F, and G are rotary exhaust valves. Steam admission was by ports in the casing end-plates, passing through the wedge-shaped passages in rotor A.

This design appeared in The Automobile Engineer, date unknown. No US patent for it has been found.

From The Book of Modern Engines by Rankin Kennedy. Volume 6, p12. Pub Caxton Publishing Company, London, in 1912.

The story of the Rotary Steam Engine continues on Page 7 of this gallery.

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