Compressed-Air Road Vehicles

Gallery opened May 2005

Updated: 7 July 2021

Yet more on the Bonnefond compressors
Back to Home PageBack to The Museum

This page refers expressly to road vehicles that are driven by stored compressed air to provide independent locomotion. Compressed-air locomotives now have their own page in the Unusual Locomotive section of the Museum.

The principle of compressed-air propulsion seems very simple. Pressurise your storage tank, connect it to something very like a reciprocating steam engine, and off you go. At least you are spared the difficulties, both technical and medical, of using ammonia, petrol, or carbon disulphide as the working fluid.

Unfortunately there are still serious problems. If you have ever pumped up a bicycle tyre, you will know that the pump body gets uncomfortably hot quite quickly. Compressing a gas generates a lot of heat, and all this energy is lost when you store the air and it cools down. The losses can be reduced by compressing the air in two or more stages, and cooling it between the stages, but they are still substantial.
At the other end of the process, using compressed air to run an engine, the main problem is keeping the system working at all. When a gas expands it gets colder, and unless the stored air is perfectly dry ice will start forming in the pipework and engine, and things will soon grind to a halt.

There is a good Wikipedia article on air cars, which gives an impressive list of their disadvantages. A non-obvious one is that it takes a lot of extra energy, apart from the compression, to dry the air sufficiently, and that energy likewise cannot be reclaimed. Compressed air cars are not a practical technology.

Compressed-air systems flourished, insofar as they did, in situations where the smoke, sparks and steam of the much more effective steam engine were not acceptable- in city streets, and down coal mines- and at a time before electricity was a viable means of propulsion. There were several compressed-air tram systems, though none proved very successful, and most were quickly abandoned. Compressed-air locomotives in mines lasted longer, but they too were eventually replaced by electric haulage. Now read on...

The first compressed-air vehicle I have found so far was devised by Bompas, a patent for a locomotive being taken out in England in 1828. There were two storage tanks between the frames, with conventional cylinders and cranks. It is not clear if it was actually built. (Knight, 1880)

The first recorded compressed-air vehicle in France was built by the Frenchmen Andraud and Tessie of Motay in 1838. A car ran on a test track at Chaillot on the 9th July 1840, and worked well, but the idea was not pursued further.

Left: The Parsey compressed-air locomotive of 1847

The reservoir A was filled with air "compressed to as great an extent as was compatible with safety" which fed chamber B, kept at engine pressure by automatic reducing valve C. Pipe D fed the double-acting engine E. At F is the air recharge valve, and G is the safety valve. The locomotive was intended for coal-mine work, but again it is not clear if it was actually built.

Source: Knight 1880

All the vehicles mentioned above were locomotives running on railway tracks. These have their own page in the Museum. This page focuses on compressed-air road vehicles.

In 1848 Barin von Rathlen constructed a vehicle which was reported to have been driven from Putney to Wandsworth (London) at 10 to 12 mph.

At the end of 1855, a constructor called Julienne ran some sort of vehicle at Saint-Denis in France, driven by air at 25 atmospheres. (350 psi)


Most of the images and much of the information on the Mékarski system are displayed by courtesy of John Prentice, whose stunning exposition of the history of compressed-air trams can be seen at Tramway Information. Do not miss it.

Louis Mekarsky (the exact spelling is uncertain) was born in 1843 in Clermont-Ferrand , in the south of France, of Polish origin.

In Louis Mekarski built a standard gauge self-contained tramcar which was tested in February 1876 on the Courbevoie-Etoile Line of the Paris Tramways Nord (TN), where it much impressed the current president and minister of transport Marechal de MacMahon. The tramcar was also shown at the exhibition of 1878 as it seemed to be an ideal transport method, quiet, smooth, without smoke, fire or the possibility of boiler explosion.

Following this success, Tramways Nord used compressed air locos to pull horse trams on their Route E, Saint Denis to Place Clichy, beginning in February 1879. Air at 25 atmospheres (350 psi) was stored in eight reservoirs 0.3 m or 0.4 m in diameter, mounted transversely under the vehicle. These were in two sets, a main and a reserve set. The two-cylinder engine drove the front axle through the usual cranks set at 90 degrees to avoid stalling at dead centre; cylinder dimensions were a modest 125 mm bore and 260 mm stroke.

The compressed-air locos were soon withdrawn due to a number of accidents, possibly caused by icing in the pipes of the brakes, which were also worked by compressed air. This strikes me as an inherently flawed concept; if you ran out of air the brakes didn't work. A car where the brakes stopped working completely if you ran out of petrol would probably not be a saleable proposition. The servo brakes fitted to almost all cars these days retain enough engine vacuum for at least one serious stop if the engine ceases to run, and when that is exhausted the brakes still work, even if some serious foot effort is required.

Left: A of a tram built by Mekarski and used in early trials in Paris. (Drawing 1875)

A train of three double-decker trams is towed by the single-storey locomotive car at the left.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 11. N° 996. Samedi 13 Juillet 1901, p170.

Left: A bouillotte mounted on the front of a tram built by Mekarski and used in early trials in Paris. (Drawing 1875)

One solution to the freezing problem was the use of the bouillotte which apparently can be translated as either "hot-water bottle" or "hotpot". This was a vertical cylinder mounted on the front platform and was 0.35 m in diameter and about 1.5 m high. It was 3/4 full of water at about 180 degC, and at about 7 atmospheres of pressure. This warmed the air and also saturated it with water vapour. As the water vapour condensed on expansion, it gave up its considerable latent heat and limited the temperature drop in the engine cylinders. The condensation may also have helped to lubricate the cylinder walls of the engine, but I would suggest it diluted the lubricating oil and caused more friction than it saved.

Note the two pressure gauges, one showing the pressure of the stored air and the other the pressure of the air leaving the bouillotte and going to the engine.

According to La Nature, the storage capacity was 2640 litres, holding kg of air at 80 kg/cm2. This weighed 262 kg at 15 degC. The range was about 16 kilometres, by which point the storage pressure had dropped to 12 kg/cm2.

Left: The regulator (air control valve) on top of the Mekarski bouillotte.

The French for 'regulator' is détendeur.

Mékarski went on to run an extensive compressed air tram system in Nantes, opening in 1879. The first trams had ten steel storage cylinders between the frames and were charged to 30 atmospheres, reduced to 4 to 6 atmospheres at the engine, which was very similar to the Paris engine. An additional 32 trams were bought between 1898 and 1900; these were more powerful than the first series, with air storage at 60 atmospheres (840 psi) and with both axles driven to improve adhesion. The compressed-air trams were replaced with electric trams in 1911.

Left: A Nantes tram recharging with air and blowing steam through the bouillotte.

The bouillotte, with its distinctive handwheel, can be seen to the left of the driver.

Mékarski system tram networks were also built in other towns in France: Vichy (1895), Aix-les-Bains (1896), La Rochelle (1899), and Saint-Quentin (1901).

There is a Wikipedia article on the Mekarski system.

Left: The regulators for the Mekarski and the Bonnefond system on top of the bouillotte.

On the right of the Mekarski regulator, there branches out a soupape de surete, a safety valve. Hopefully the Bonnefond system had one too. Note the Belleville springs on the Bonnefond regulator.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 11. N° 996. Samedi 13 Juillet 1901.


The water in the Mekarski bouillotte cooled quickly as air was blown through it, and it was initially reheated by blowing steam through the water when the tram stopped to recharge the air tanks. Later a certain Monsieur Bonnefond introduced an internal coke firebox to provide continuous reheating of the water. This approach appears to have only been used in the Paris operations of the Compagnie Générale Des Omnibus (CGO).

Left: A compressed-air tram of the Compagnie Générale Des Omnibus of Paris, system Bonnefond

The access panels have been lifted to show the compressed-air engine on the left, and what is presumably an emergency tank for the air-brakes on the right. The Bonnefond bouillotte is at the extreme right.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 11. N° 996. Samedi 13 Juillet 1901.

Above: Side view of CGO tram: 1901

In the centre is the compressed-air engine. To the right is the braking equipment.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 11. N° 996. Samedi 13 Juillet 1901.

Left: The Bonnefond bouillotte

In the right-hand drawing, the chimney can be seen at lower left.

In the right-hand drawing, the two pressure gauges showed the storage pressure, and the pressure applied to the cylinders after it had been through the bouillotte.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 11. N° 996. Samedi 13 Juillet 1901.

Left: The Bonnefond bouillotte

The Bonnefond system is all very well, but you immediately lose the main advantage of compressed-air power; ie the absence of smoke, ashes and potentially hazardous sparks. There is also the stimulating possibility of a boiler explosion. Considering that the driver already had his hands full dealing with the uncertain braking system, to expect him to stoke and supervise a small steam-boiler as well seems rather rash.

Note the butterfly valve at B to close off the chimney while dropping coke into the firebox.

When the tram was recharged it was necessary to take on water and coke as well as compressed air.

According to La Nature again, the Bonnefond bouillotte consumed 0.6 kg of coke per kilometre; not a negligible amount..

Compressed-air trams need a network of refilling points to recharge their storage cylinders, supplied by a central compressor station. For this purpose COG built a large usine (power-plant) at Billancourt on the bans of the Seine, to the West of Paris.

Left: The compressor hall at the Billancourt usine in Paris.

The total output of the usine was 7000 horsepower; it supplied air at 80 kg/cm (1140 psi) to a distribution network of pipes. The usine was built on the banks of the Seine to give ready access to water for the condensers.

Seven large steam-engines constructed by Dujardin et Cie of Lille drove the compressor. They were horizontal three-cylinder triple-expansion engines, each normally giving 750 HP at 52 rpm, but they were capable of giving 1000 HP at 70 rpm. Each engine drove a three-stage compressor, with water injection to reduce losses.

The four smaller engines in the foreground (made by the same firm) were installed to provide auxiliary power, such as lighting electricity.

Only the flywheel at lower right appears to be turning in this photograph, (no spokes visible) and theres's not a soul to be seen. Clearly a quiet day...

On a closer look there is one man visible, standing behind the left-hand end of the first large steam engine.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 12. N° 997. Samedi 20 Juillet 1901.

Left: The compressed-air distribution network of the CGO in Paris: 1901

The CGO air network was wholly separate from two other compressed-air networks in Paris; the power network and the clock network.

The island in the Seine on which Notre-Dame is built can be seen at extreme right.

The Eiffel tower is just visible as a small square at top left of the area labelled 'Champ de Mars'.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 12. N° 997. Samedi 20 Juillet 1901.

Left: The boiler hall of the Billancourt usine of the CGO: 1901

There were 16 boilers made by Babcock & Wilcox. All boilers were to the same design, having 210 square metres of heating surface, divided into 12 sections of 9 tubes each. Boiler pressure was 12 kg/cm. (171 psi)

There was a passage running behind the boilers, topped with a round arch; this collected the exhaust gases from each boiler. At either end of the passage was a chimney.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 12. N° 997. Samedi 20 Juillet 1901.

Left: Centrifugal pumps for raising water from the Seine at the Billancourt usine: 1901

These pumps were housed in a small building adjoining the compressor hall. They were driven by one of the auxiliary engines, by means of a belt passng through a slot in the wall. The water was used for condensing and boiler feed. (after purification)

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 12. N° 997. Samedi 20 Juillet 1901.

Left: 750 HP compressor in the Billancourt usine: 1901

The Billancourt usine used three-stage compression. The vertical compressor standing here performed just the medium and high-pressure stages. The low-pressure stage is the horizontal cylinder on the extreme left. Note the hefty size of the connecting rods and piston-rods; serious forces were involved.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 12. N° 997. Samedi 20 Juillet 1901.

Left: 750 HP compressor in the Billancourt usine: 1901

The vertical compressor standing here performed just the medium and high-pressure stages. The medium-pressure cyinders are just above half-way up, and the smaller high-pressure cyinders are at the top.

The vertical cylinders marked V, V' in the left-hand diagram are air dryers of 450-litre capacity, one for each pair of compressor cylinders. That marked V has a spring-loaded safet valve Air leaves the top of the dryers via the pipe X. The vessel K is a 200-litre receiver between the medium and high-pressure cylinders.

The spiral thing between the two medium-pressure cylinders (marked M but this is not legible here) is an intercooler between medium and high pressure stages. The spiral pipe was immersed in water at ambient temperature.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 12. N° 997. Samedi 20 Juillet 1901.

Left: 750 HP compressor in the Billancourt usine: 1901

This shows the medium and high-pressure cylinders only. Note safety-valve P.

This gives a better view of the receiver K and the intercooler M.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 12. N° 997. Samedi 20 Juillet 1901.

Left: 750 HP compressor in the Billancourt usine: 1901

It is not fully confirmed but it appears that the large horizontal cylinder handled both the low-pressure steam (left of piston) and the low-pressure air compression. (right of piston- note valves) A pump injected water into the low-pressure cylinder via the small pipes D, to reduce heating and improve efficiency. The diameter of the cylinder was 1 metre.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 12. N° 997. Samedi 20 Juillet 1901.

Left: Air inlet valve for the low-pressure stage of the Billancourt compressors: 1901

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 12. N° 997. Samedi 20 Juillet 1901.

Left: Valves of the Billancourt compressors: 1901

Fig 3 (Left) Drain valve for the high-pressure stage.

Fig 5 (Right) Delivery valve for the low-pressure stage.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 12. N° 997. Samedi 20 Juillet 1901.

Left: Water injection pump for the Billancourt compressors: 1901

F,F bouchons de regard = inspection ports

H Boite de refoulement = discharge box; this seems to have been an air vessel to reduce pressure fluctuations in the discharge

K Tuyau de refoulement = discharge pipe

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 12. N° 997. Samedi 20 Juillet 1901.

Left: The Billancourt usine of the CGO with its two chimneys and water-tower: 1901

At the northern end was a conventional brick chimney 60 metres high and of internal diameter 2.5 metres at the top. At the southern end was a remarkable conical chimney 32 metres high, built of sheet metal to Systeme L Prat; this had an artificial draught powered by one of the auxiliary engines. Presumably the cone was intended to act as a diffuser, reducing the amount of energy required to create an adequate draught.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 12. N° 997. Samedi 20 Juillet 1901.

Left: The Billancourt usine of the CGO: 1901

Here the conical chimney appears to be blasting its smoke into the sky under pressure.

There were at least three members of the Prat family, and they took out at least two USA patents. The chimney company name translates as "Society of Chimneys L Prat of Induced Draught" and it was based in Paris.

(From the Official Gazette of the United States Patent Office, Volume 310)

The chimney looks very much like a hail cannon, used to (allegedly, but not really) prevent hailstorms. The large wooden structures are cooling towers for the condenser circulating water.

Source: Le Genie Civil Vingt-unième année. Tome XXXIX No 12. N° 997. Samedi 20 Juillet 1901.

Left: The Billancourt usine of the CGO with its two chimneys:

The Society of Chimneys was apprently still going strong in 1928, as 6 US patents were lodged.

From the Annual Report of the Commissioner of Patents 1928, p434

Main pic source: Le Genie Civil Vingt-unième année. Tome XXXIX No 12. N° 997. Samedi 20 Juillet 1901.

Left: The Billancourt usine of the CGO with its two chimneys: 1901

The entrance to the usine site.

Above: Plan of the Billancourt usine of the CGO: 1901

At the top is a parc a charbon. (coal storage area) Below that is the compressor hall, and below that the boiler hall. Below that again is another parc a charbon, and below that a bank of accumulators for storing compressed-air. The supply pipes are shown as dashed lines. To the left is the River Seine, and on the right are three areas of land; the top one has not yet been built on.

Above: Side view of the Billancourt usine of the CGO: 1901

At the top is a side view of two of the four auxiliary steam-engines. At bottom is a side view of a main engine and its vertical compressor, with a boiler to the right.


Compressed-air trams were tried in East London, Wantage, the Vale of Clyde, Liverpool and Chester. Various designs were used. None of the trials lasted long; the cost of operation proved excessive.

The Wantage experiments used two Mékarski-type trams built by the Compressed Air Engine Co Ltd, of 19 St Swithins Lane, London EC. The air was preheated by some sort of bouillotte, which raised its temperature to 312 degF, doubling its volume. Compressing plant costing £2000 was installed at Wantage Town tram terminus. A single-acting compressor pressurised six large air receivers to 450psi. Recharging a tram took 15 minutes. Quite why it took that long to fill the compressed air tanks is not easy to understand- for me anyway.

The range of the compressed-air trams was barely sufficient for a round trip. Matters were not eased by the 1:47 gradient at the end of the route, when the air pressure was at its lowest. The first compressed-air journey was made on Thursday evening, 5th August 1880

Mr. G. Stevenson, the line's engineer, estimated that the compressor used about 24 cwt of coal per day, but on such a sparse service this was far too high, as steam locos would only use 5 cwt per day.


These articles are taken from the journal Manufacturer and Builder:

Street Cars Run by Motive Power

"The Second Avenue Railroad of New York city, has one of the Pneumatic Tramway Engine Company's cars. Upon each platform is a steel lever, by means of which the car can be started, stopped or its direction reversed. The car is of the same general model as that of ordinary street cars. It has six tubular air receivers situated under the floor of the car. The air is compressed by an engine which is standing at the side of the depot, and is introduced by a rubber hose into these receivers. That air passes through an engine situated between the axles, and propels the car."

"The car lately ran from 63d to 95th street and back in about 20 minutes, with two or three stoppages. It is claimed for the car thus inspected that it can be stopped more readily than the horse cars, and that its rate of speed can be increased to 30 miles per hour, while it can make 9 miles per hour and still not appear to go faster than the horse cars. The car which was run is only a model, and it takes about four hours to charge its receivers with air, but machinery has been ordered which will perform the work in less than a minute."

"One of these air engines, it is said, can easily draw a whole train of ordinary street cars. A company composed of 25 capitalists has been formed to manufacture cars upon the above model. It has already received an order for five from the Second Avenue Company. These will be used on the upper part of the Second Avenue route."

Source: Manufacturer and Builder Volume 10, Issue 5, May 1878

Compressed Air Locomotives in New York City:

"The Third avenue horse railroad has now in operation one small locomotive, which is used instead of a span of horses to propel one of their ordinary cars. The machinery is partially on the front platform and partially below the bottom of the car and under the side seats, which will accommodate about half the number of passengers that the car will hold. The propelling power is compressed air, which is stored up at the depot up-town by a stationary engine, and tapped by the car from its reservoir at every trip, the capacity of the reservoir in the car being sufficient to contain compressed air enough for a down and up trip."

"It appears to give satisfaction so far, and if this continues, it will afford great relief to the horses, which, when used on street cars, suffer much from the continual stopping and starting connected with this mode of travel. The Society for the Prevention of Cruelty to Animals will, we hope, encourage this new enterprise."

Source: From Manufacturer and Builder Volume 11, Issue 11, November 1879

Revival of the Use of Compressed Air as a Motive Power
By Dr P H Van Der Weyde

"Lately an important problem has again been brought to public notice -- namely, the propulsion of street cars by means of compressed air, carried on the car itself."

"The solution of the problem requires the execution of two kinds of contrivances -- first, a reservoir strong enough to withstand considerable pressure, and, secondly, a motor machine to be put in operation by this pressure. The reservoir is by preference made in the form of cylinders, of say one or two feet in diameter, so that they can be placed under the seats of the car, and of a length sufficient to utilize all the space afforded. The motor is best placed under the floor of the car, now a common method in the electric trolley cars, while the regulating devices are on both platforms where the motorman performs his duty."

"It is evident that this system offers peculiar advantages, especially by reason of its apparent simplicity. The cylinders containing the compressed air -- the motive power -- are charged at the station and need no further attention, as is the case with locomotive boilers, where the chances of safety depend on the engineer and stoker. All the heavy machinery used for the production of the primary power is stationary, and no power is wasted to move it about as in the case of the locomotive, the only weight to be transported is the motor and the cylinders containing the compressed air. Summing up the advantages, they are:"

1. No dead weight of coal or fuel on board.

2. No dead weight of water, boiler, furnace, and other material which has to he stabled, the real primary motor, which is a stationary structure of large dimensions, and therefore economical, as the economy increases at a very large ratio as the engines are increased in size.

3. The compression of air is going on continually in the reservoirs, and is always connected with the gauges, so as to insure safety.

"The first application of this principle was seen some six or eight years ago at the Harlem station of the Second Avenue Railroad. It was intended for the propulsion of trains, and the compressed air reservoirs consisted of two huge cylinders placed horizontally, with a space between, through which the engineer could see the forward track while standing on the motor, and having the train of cars behind."

"A few years later I saw some interesting experiments of thie same character at the Delamater works, where pipes were laid to quite a distance from the works, and at which pipes the cylinders could take up new supplies of compressed air without going back to the supply station."

"A syndicate has been formed to introduce this system of street transportation, so that we will have another additional method in practice."

Source: From Manufacturer and Builder Volume 26, Issue 12, December 1894


Left: A Compressed-Air Tricycle for mail delivery

Nothing is currently known beyond the information in the New York Times article. No US patent appears to have been taken out by either Hartley or Stoll.

If the compressed-air-tank was installed "under the handle bars" this seems to indicate it wasn't very large, and it seems surprising that such a tricycle could cover thirty-three miles. Perhaps in reality it couldn't.

Thanks to Bill Levine for bringing this to my attention.


Left: The Pneumatic Carriage Company's compressed air car: 1898

The Pneumatic Carriage Company of New York City developed a car that ran on compressed air. The air is believed to have been stored in a steel cylinder running the length of the lower body; the storage pressure is not currently known.

From The Horseless Age for October 1898:

"In 1895, the Pneumatic Carriage Company was organized under the laws of West Virginia, with an authorized capital of $5,000,000, and with offices at 253 Broadway, New York. The organizers had been conducting experiments with compressed air motors for street railway service for several years, and naturally turned toward the motor vehicle when it received its first impetus in America. The president and manager of the company is A. H. Hoadley, who has been in charge of the experiments at the works of the American Wheelock Engine Company, Worcester, Mass.

The first carriage built by the company, illustrated herewith, was completed in November, 1896. It has seating accommodations for six passengers, weighs 2700 pounds, and will run 20 miles over ordinary good roads on one charge. A grade of 20 per cent is claimed to be surmountable. The wooden wheels are 30 and 42 inches respectively, and pneumatics of 4 inches diameter render riding as easy as possible. The motor, of the reciprocating type, weighs 400 pounds and operates at 350 revolutions, when the carriage is making 15 miles an hour. Ordinary compensating gear and hub steering are employed. In order to heat and expand the air before it enters the motor, it is surcharged with hot water, carried in the vehicle in a separate tank and kept at a temperature of 400 degrees Fahrenheit. Five pounds of water are required for each mile traversed. All the above machinery is spring-supported, to relieve it from the shocks of the road.

This carriage has been tested for the past year or more in the streets of Worcester and Washington, DC"

This account positively bristles with impracticalities. Note the very limited range, and the need to carry around a tank of hot water to heat the air; if five pounds of hot water were expended per mile, and the range was 20 miles, the contents of the full tank would have weighed 100 pounds. The engine appears to have been extraordinarily heavy at 400 pounds.

Note that the hot water was stored at 400 degF. The normal boiling point of water is 212 degF, so clearly it was stored under pressure. In fact, under considerable pressure, because water boils at 400 degF at about 230 psi- a greater pressure than that used in most steam boilers of the day. The water tank would have to withstand this pressure, so it would have to be a lot stronger and heavier than a simple tank. This clumsy and potentially dangerous setup seems to indicate that the Pneumatic Carriage Company had considerable difficulty in storing enough energy to heat the air, even for the very limited range that was claimed.

Therefore "filling up" would be quite a business. You would need a filling station that not only had a supply of compressed air (which I suspect was at considerable pressure- the later Mekarski system stored air at 60 atmospheres = 840 psi) but also a constantly-hot steam boiler working at an unusually high pressure. And with a 20-mile range you would need an awful lot of filling stations. You can see why this idea did not take off.

The following news item provides a little more information:

"A Compressed Air Carriage. Nov 1896"

"For some time past experiments in compressed air motors have been conducted at the factory of the American Wbeelock Engine Company, Worcester. Mass. These experiments have been very exhaustive, covering the application of compressed air motors to both track and road vehicles. To gather data for tbe latter class of vehicles, the Pneumatic Carriage Company, which is the name of the company working in this particular line, have just completed a two-seated carriage, which was publically exhibited in a procession held on Flag Day, Oct. 31, through the streets of Worcester, although close inspection was not allowed, inasmuch as tbe present vehicle is merely experimental and the company are not yet prepared to furnish specific information. President Hoadley states, however, that the experiments will be continued until a thoroughly satisfactory model is obtained, when steps will be taken to introduce compressed air vehicles for public service in cities."

"The Pneumatic Carriage Company has New York offices at 3S3 Broadway, connected with those of the American Wbeelock Engine Company."


Left: The Air Vehicle Company car: 1900

This air-propelled car was constructed by Charles D P Gibson. The engine was 'the usual two-cylinder type' and weighed 36 pounds. The total weight of the car was 670 pounds.

The air was stored at a pressure of 2,500 psi and reduced to an initial cylinder pressure of 150 psi by reducing valves, which were under the control of the driver and allowed the working pressure to be regulated as required. A device for heating the air was used.

Compressed Air reported:

"On a recent trial on a bad road this wagon was operated with a consumption of 60 cubic feet of free air per mile. The condition of the road was much below the average, and the trail was not one which would give the most economical results in the use of the power, yet under these conditions it would be seen that the storage has capacity to run the wagon 20 or 30 miles. And as it is estimated that air can be compressed for less than 4 cents per 1,000 cubic feet, it is believed that it will prove a desirable and economical power for propelling omnibusses and delivery wagons which have a definitely determined route to travel."

Source: Compressed Air, Volume 4, Jan 1900, p829


Left: Drawing of the Airmobile from above: 1914

Two engineers, C R Harris and Rutherford G. Goldman (who as an artillery artificer in the Spanish-American War, earned a medal for heroism), applied for a patent for a rotary fluid-brake in September 1911; US patent 1,127,237 was granted in February 1915. This brake appears to have been some sort of radial air compressor, though this is currently speculative.

From this grew the idea of a compressed-air propelled car called the Airmobile. The historical record is rather vague, but it appears that by 1914 Harris and Goldman were preparing to produce a car that had four-wheel rotary air-brakes which also functioned as air-motors, and also two air storage cylinders and an engine-compressor combination. The engine was claimed to be a “frictionless rotary engine fueled by crude oil” a description that rather undermines one's confidence. It is not clear if this was rotary engine in the Wankel sense, or a misdescribed radial engine. The air compressor is also described in the drawing as "frictionless". Oh really?

Given the relatively small amount of air storage provided, the whole compressor/air-motor system is just a very cumbersome and inefficent transmission system. It appears that all the heat generated by air compression was simply thrown away. To add to the complications, the suspension was partly by pressurised air-cushions, with their own air reservoir; see extreme left of drawing. In the drawing above the air-motors on each wheel are shown as no larger than an ordinary hub, and I doubt if this was realistic. Having four motors rather than one central motor much increases the complexity, and presumably also the unsprung weight. No means of preventing the air-motors from icing up is visible.

The 25 December 1916 issue of “The Automobile Journal” published a section titled “Novel Power Plants” (page 21) in which the following appeared on page 26:

“Features of the New Airmobile.

“THE Rotary Products Company, Los Angeles, Cal., has adapted the rotary principle of generating power from gasoline and storing It as compressed air by driving an air compressor, designed on lines similar to the engine, and In turn piping the air to rotary air motors attached to each of the four wheels. This Is probably the most unique Idea In motor car propulsion that has been presented this year.

“Its practicability rested with the perfection of the rotary principle which Involved largely the question of maintaining the necessary pressures In the explosive chambers which heretofore has been impossible because of leakage. The maker of this motor, however, claims that leakage has been negatived and that the engine can be run at low speed and produce high pressures, whereas formerly rotary engines were run at high speed and only produced low pressures.

“A further and Interesting fact about the mechanism Is that It Is applicable not only as a rotary gasoline engine, but as an efficient air compressor, an air motor or can be adapted as a clutch or brake. The rotary engine is used to drive a rotary air compressor, both machines being hung on cross members in the forward part of the chassis. The air Is stored In tanks and piped to the four wheels, which are operated by individual air motors, or as brakes.

“By this method of generating and transmitting the power the maker claims to have obtained not only a frictionless drive, but to have eliminated crank and camshafts, flywheel, clutch, transmission, levers and friction brakes; reduced weight and cost of construction and incidentally have adapted a set of air cushions which supplement the springs and reduce the vibration to a minimum.”

A somewhat less than perceptive account.

No production vehicles resembling the drawing above were ever produced, and it appears that the idea was abandoned sometime around 1916.


Left: The Lee Barton Williams compressed air car: 1926

A compressed-air car was built by Lee Barton Williams in 1926. Williams was from Pittsburgh. He claimed the car started on gasoline but on reaching 10 mph it switched to compressed air only. His refusal to give any technical information suggest that he was either deluded or planning some sort of scam.

In August 1940 Williams was granted US patent 2,211,996 for a 'propellor' of eccentric design. It seems to have nothing to do with compressed-air cars.


Left: The F E Kenney compressed air car: 1926

This description sounds like it comes from Popular Mechanics or a similiar journal:

"A working model of an air-driven hydraulic motor, involving a new principle in automobile reconstruction, had been perfected by F.E. Kenney, Portland, Oregon, mechanical engineer. The machine is operated in much the same way as a locomotive or steam engine, except that air pressure instead of steam pressure is utilized as motive force. Power is derived from a small electric motor run by current from a storage battery. The motor operates an air pump which keeps up pressure in the tank. The compressed air, mixed with oil, is admitted to two hydraulic cylinders, where it drives the pistons."

Two cylinder heads are visible in between the chassis frames; it is not clear if these are part of a compressor, part of an air motor, or one of each. To their right are two tanks, presumably for storing the compressed air.

As described it's just another failed attempt at perpetual, or near-perpetual, motion. If the power comes from a small electric motor, why not connect that directly to the wheels instead of going through a ludicrously inefficient pneumatic-hydraulic transmission system? As with other projects of the type, there was probably enough air in the storage tank for short demonstrations, whether the electric compressor was working or not.

The vehicle appears to be a conversion of a Model-T Ford.

In this rather odd picture the car appears to be displayed in a shop window, (though it does not look ready for public viewing) with Kenney dourly turning his back on the onlookers. In the foreground is a 6-Volt battery.

Left: The F E Kenney compressed air car: 1926

This is probably the same chassis as in the photo above, but the dashboard and the mechanical arrangements look different.

At the front of the car, where the engine would normally be, is an electric motor. The rear of the car carries a big battery, and the fuel tank (?) visible at the rear of the photo above has gone. Once again, two cylinder heads are apparently visible, but what they mean is obscure. No compressed-air tanks can be seen here.


Left: The Roy J Meyers Air car: 1932

This car was not so much a practical proposition as a perpetual-motion fraud. The text says air is heated electrically until it reaches 200 psi. It then powers the motor and is 'recovered and drawn into a compressing chamber, where it is heated again and returned to the tank.' This sounds like a hot-air engine, with the energy supplied by that electrical heating. The electricity is suppplied by a battery and generator- so what powers the generator? It would have to be a sizable petrol engine to supply all the power continuously, in which case the compressed air is just acting as an inefficent transmission system. However I have a deep suspicion that the generator was connected to the air motor, to give a good old-fashioned perpetual motion machine. How else to interpret 'not one cent of cost to the driver for fuel'?

The question is not clarified by the four big cylinders on the back of the car. These are described as 'fuel tanks' in the caption to the illustration, while in the illustration itself they are clearly labelled 'compressed air tanks' which is exactly what they look like. I suggest that the real power source was air stored in these tanks, which would be sufficent for short demonstrations but certainly not for journeys of 500 miles.

Roy J Meyers had a colourful history, which included a 3-1/2 year sentence in the Arizona state prison at Florence; what for does not seem to have been recorded. While there he claimed to have invented an 'Absorber' which could extract electricity from the air and give free power. This appears to have been around 1912. He planned to build a 200-foot Absorber that would power the city of Phoenix; unsurprisingly it was never built. Meyers has become an icon for those seeking free energy. See, and also for some of his rivals, but he was clearly at best deluded, and more probably a con man. 3-1/2 years for confidence trickery sounds about right.

The six-cylinder radial engine is interesting; note the small intake manifold and the large exhaust manifold.

This article appeared in Modern Mechanix for Jan 1932.

Left: The Roy J Meyers Air car: 1932

This photo gives a good view of the six-cylinder radial engine. So far as I can see there are no fins on the cylinders to combat icing.

From Popular Science for Jan 1932, p58

Left: Roy J Meyers patent: 1926

It did not take the Museum staff long to track down two patents by Meyers. The first (US 1,550,833 of 1925) is a bizarre brake that has its friction surfaces immersed in oil. The second patent (US 1,608,802 of 1926) is more to the point; it is called 'Fluid Pressure Generator' and is clearly the technology- if it might so be called- on which the Meyers car was based.

The operation is thus. Electricity from battery g heats the wires 10 inside pressure chamber A, and the air around them expands and rushes through the Giffard injector 23, pumping air into pressure chamber B. From here it passes to A through check-valve 8, keeping the pressure up despite air being drawn off at 46 to run the car. Items 31 and 32 are air reservoirs (the ones on the back of the Meyers car) and 33 is an air compressor to get the whole business started. What drives that is not stated.

Yes, it's a good old-fashioned perpetual motion machine of the First Kind, and how it got past the US patent examiners I do not know.

The Giffard injector, invented by the remarkable Henri Giffard, is a perfectly respectable device. It uses the pressure of a steam boiler to force in fresh water, naturally against the same steam pressure. This sounds impossible but it is not- the secret is that part of the steam condenses in the water being injected, using energy, and this makes it all thermodynamically possible. Nonetheless the operation appears paradoxical, and in the early days there were many who refused to accept it could work.

This paradox caught the eye of free-energy enthusiasts, who convinced themselves that this could work with an air tank. Compressed air from the tank would be fed to an injector, which would stuff that air, plus more entrained from the atmosphere, back into the tank. This is impossible, because no condensation occurs, and there is also the little matter of the Law of Conservation of Energy. It would be a bizarre universe in which this could work; presumably the air pressure would increase without limit, or at any rate until the tank burst.

This self-refilling perpetual motion scheme resurfaces from time to time, always with the assumption that just the right combination of injectors and check-valves (there are always lots of check-valves) will make it work. The phrase 'free-range air car' is likely to crop up and should be a warning to the reader. To get a taste of this stuff try 'Suppressed inventions' often crop up; see this site. That is just the page which includes the Meyers car.

One thing is clear. The arrangement in the patent will provide compressed air- for so long as that stored in the air reservoirs lasts. This should be long enough to impress potential investors...


There are several on-going projects for air-driven cars; see Wikipedia. The page includes a daunting list of air-car disadvantages.


The French MDI Air Car is apparently no longer a live project; the domain name is for sale. Apart from straightforward compressed-air propulsion, they claimed to be also developing dual-energy engines, in which a fuel (petrol, diesel, oil, alcohol or gas) is burned in an external continuous combustion chamber to heat the air and give more range. The amount of toxic gases released was claimed to be very low.

One of the vehicles proposed had the following specs:

Weight Empty
220 kg
Max speed
70 km/h (43 mph)
Range (urban)
220 km (136 miles)
Reservoir Pressure
350 bar (5076 psi)
Reservoir Volume
175 litres
Refill Time
1.5 minutes

The following publicity material was released. After a lot of guff about internet connectivity, GSM telephone connectivity, a GPS guidance system etc, etc, which had nothing to do with the means of propulsion:

"The Mini C.A.T is a simple, light urban car, with a tubular chassis that is glued not welded and a body of fibreglass...

"Most importantly, it is incredibly cost-efficient to run – according to the designers, it costs less than one Euro per 100Km (about a tenth that of a petrol car). Its mileage is about double that of the most advanced electric car (200 to 300 km or 10 hours of driving), a factor which makes a perfect choice in cities where the 80% of motorists drive at less than 60Km. The car has a top speed of 68 mph.

"Refilling the car will, once the market develops, take place at adapted petrol stations to administer compressed air. In two or three minutes, and at a cost of approximately 1.5 Euros, the car will be ready to go another 200-300 kilometres. As a viable alternative, the car carries a small compressor which can be connected to the mains (220V or 380V) and refill the tank in 3-4 hours.

"Due to the absence of combustion and, consequently, of residues, changing the oil (1 litre of vegetable oil) is necessary only every 50,000 Km.

"The temperature of the clean air expelled by the exhaust pipe is between 0 - 15 degrees below zero, which makes it suitable for use by the internal air conditioning system with no need for gases or loss of power."

Elsewhere the claimed top speed was very modest, at 43 mph, and the range less than stunning at 136 miles. The company made the usual claims about the car being pollution-free, which is of course true in actual operation. But since compressed air is being used merely for energy storage, power will have to generated somewhere else. And proponents of air cars never mention that compressing air is inherently inefficient, with all the heat of compression lost.

The air storage tank was to be made of carbon-fibre wound on a thermoplastic liner. Kerry Stiff tells me:

"The storage vessel they were using is known as a Composite Overwrapped Pressure Vessel or COPV. COPVs are expensive, fragile and dangerous. They have a limited number of fill-discharge cycles. There is a pressure at which the overwrap fibre goes from compression to tension. Every time you cross this pressure value, rising and falling, you use up one cycle. COPVs must be filled very slowly to prevent overheating."

"NASA uses COPVs with great caution. The procedure for charging COPVs at KSC is so onerous that we charged them at CERN. These COPVs were not certified for transport under pressure on public roads. We had the road closed from CERN to the Geneva airport so we could transport AMS to the airport. AMS was airlifted to KSC by a US Air Force C5-M. The C5-M landed on the shuttle runway at KSC alleviating DoT issues in the USA. This was the coolest airplane ride I have ever had!"

As of 2018 no MDI design had reached production. There is a Wikipedia page on MDI.


Left: Peugeot: 2013

This project used a car with a conventional petrol engine, plus regenerative energy storage in the form of compressed nitrogen. The project was begun in great secrecy in 2010, and a car was supposed to be in production by 2016.

The basic idea of the Hybrid Air car was to make an efficient hybrid vehicle that did not have to carry around a great weight of batteries. The main power came from a conventional petrol engine, coloured red in the illustrations. Instead, on braking or slowing down a hydraulic pump/motor (coloured green) pumped oil to compress nitrogen stored in a four-foot long gas cylinder, with a maximum working pressure of 3600 psi. When the stored power was needed for acceleration the compressed gas pushed the oil back through the pump acting as a motor.

The middle illustration shows the oil/nitrogen reservoir in the centre of the car. The extra green tank at the right holds a reserve of hydraulic oil.

In 2015 it was announced that the project had been put on indefinite hold.

Why? Here are my thoughts:

  1. There is a lot of extra weight to carry around; the hydraulic pump/motor, the nitrogen cylinder, and the charge of oil. In particular, a gas cylinder that can safely withstand 3600 psi, even in an accident, is going to be heavy.
  2. There is a lot of extra stuff to go wrong.
  3. The amount of energy that can be practically stored, even at 3600 psi, is small.

Perhaps I'm missing the point, but I would have thought a few back-of-an-envelope calculations would have shown this wasn't a good project right at the start.

Image & info from the Observer 24 Mar 2013, p18

Left: Computer rendering of the Peugeot car: 2013

This shows that the oil reserve tank at the back is actually quite big. Its shape and colour suggest that it is under the same pressure as the central cylinder. More expense!


Searching for 'air cars' with Google rapidly brings up the Zero Pollution Motor Company, who are promoting the Airpod 2.0 compressed air-powered car. (sic) Judging by the pictures available, the car itself has indeed been compressed. Their website shows lots of renderings but as far as I can see no real hardware. They are looking for investment...

Left: ZPM Airpod 2.0: 2018

I think this is just a rendering. I wonder what happened to Airpod 1.0

Some technical details have been released. The compressed air engine is reversible, (?) and has two in-line cylinders with variable valve timing. The capacity is only 430cc (26.2in³). The crankcase and cylinder head are aluminum. Each cylinder is described as having having 'an included active chamber'; this seems to refer to some sort of auxiliary piston that prevents dead-centre issues, though there shouldn't be any with a two-cylinder engine. The engine is currently somewhat mysterious.

Drive is to the rear wheels through an automatic gearbox with 3 gears + reverse. If there is a reverse gear it's not obvious why you need a reversible engine; perhaps it refers to using the engine as a compressor. There is claimed to be electronic management of kinetic energy recover during deceleration, and presumably this refers to recompressing air.

We now come to the all-important air storage tank. This is spec'd as "Type IV, thermoplastic liner and carbon fibre wiring. Volume: 2 × 125 litres. Pressure: 248b". Presumably this means two tanks at 248 Bar, which is 3600 psi in round numbers. Tank design is said to be based on EC norm ECE R110, which is titled “High pressure cylinders for the onboard storage of natural gas as a fuel for automotive vehicles". Research shows that this standard does cover wound cylinders. See here.

ZPM claim to have a license from MDI (above) which given MDI's uncertain status is perhaps not reassuring. The claim of zero pollution of course ignores how the energy to compress the air was generated.


The Odd Bicycle gallery of the Museum has a projected compressed-air bicycle as an exhibit. It looks completely impractical.

One of the most prestigious of the early motor cars was the French built Delaunay-Belleville. They built some big cars with 11.8 litre engines for the Russian Tsar in 1909. These were fitted with Saurer compressed-air starting gear, which could also be used to inflate tyres, jack up the wheels, or blow a whistle. However its most important feature was that the air reservoir was sufficient to drive the car for about 400 yards without even starting the engine, allowing the Tsar to make a quick getaway from an assassination attempt.

Given the history of Russia, this was not just a theoretical possibility. Tsar Paul I was murdered in his own bedoom in 1801. Alexander II survived assassination attempts in 1866, 1879 (twice), and in 1880, when the dining room of the Winter Palace was blown up, before he finally ran out of luck in 1881.

There is, of course, another and far less benign class of things very often powered by compressed air: torpedoes.


This intriguing kit was spotted in the gift shop of the Science Museum in Milan. It is a very fine science museum, though for obvious historical reasons they do bang on a bit about Leonardo da Vinci. My view is that anyone can design a helicopter that does not work.

Working solely from the picture, the engine seems to be two very simple single-acting cylinders (to avoid dead-centre problems) driving a common crankshaft in the upper forward part of the grey chassis. There are then at least two stages of reduction gearing in the drive to the rear axle. How the crankshaft connects with the first spur gear (with the green segments) is unclear.

The info on the back of the box (see below) says there is a pump-up bar, a pressure gauge and a safety valve, none of which are visble. The round thing at the back of the air reservoir appears to be the on/off valve. I have no idea what pressure is used or how far this thing will run.

Author's photo. Milano May 2018.

The information on the back of the box. The text under the reflection is 'NO BATTERY'.

Author's photo. Milano May 2018.


Compressed air vehicles in general:
Interesting historical material, but some worrying references to what appears to be perpetual motion.

For French references, Google on "locomotive à air comprimé". For example: tramways_mecaniques

Porter locomotive links:

Back to Home PageBack to The Museum EntranceTop of this page