Chapter 13
The Serpollet Car
Although the early steam carriages of the thirties attained a fair amount of success, and on the Continent there were no vexatious and restrictive laws as in England, it was not till the advent of the petrol engine that any great strides were made. Many French and German engineers had tried their hands at steam carriages, but not with any great success. Leon Serpollet, of Paris, had experimented for many years, and sold a good many steam cars before the petrol car appeared, but the demand for tramway vehicles for a long time drew his attention from the light road carriage. One of his carriages was brought to England and shown in the yard of the works of Messrs. Bryan Donkin and Co. In 1890, and the following year the writer, when on a visit to Paris, had a ride with M. Serpollet through some of the busy streets of Paris, and in the suburbs, when on a level stretch, a speed of fourteen or fifteen miles an hour was attained.
It is presumed the reader has some acquaintance with the working of the steam engine. The ordinary locomotive boiler is far too heavy for a light machine to carry two to six passengers. Therefore, Serpollet designed and made light boilers of a non-explosive type, which would carry very high pressures. These boilers may be described by reference to the so-called geysers, for heating water for baths. A coil of pipe heated by gas, or sometimes an oil burner, has a stream of water running through it. The cold water enters generally at the top, and passing down runs out at a high temperature. The temperature being regulated either by the heat of the burner or by the quantity of water flowing through the heated pipe. Serpollet’s boiler may be explained by carrying this idea further. If the heat in the geyser be very great in proportion to the water flowing through, steam will be generated, and blow out at the end of the pipe. In the original Serpollet boiler the tube, which was in one continuous length, was flattened so that it should contain as little water as possible, and heated over a coke fire, the coke falling down a hopper as in the tortoise stove used for greenhouse heating. In the tramway engines this arrangement is still in use, but for light pleasure carriages the coke is replaced by oil - heavy oil as used in lamps. This is burnt in what are known as the Swedish burners, and which, when well alight, emit neither smell nor smoke, the consumption, however, being very much greater than if the oil were burned in the cylinder of the engine as in true oil engines, but it must be remembered that lamp oil is only about half the cost of petrol.
There have been very many alterations in the design of the vehicles, engines, and boilers - in fact, it is difficult to see the object of many of the alterations and supposed improvements, but the carriage appears now to have reached, if not a final type, at least a type which is well on the market, and probably will be a permanent design for some years.
One drawback with the Serpollet system is the super-heating of the steam; steam at atmospheric pressure has a temperature of 212° F; at 100 lbs. square inch it is 328° F; at 180 lbs. (a pressure often used in the modern locomotive) it is 372° F. Above this temperature the steam acts injuriously on the bore of the cylinder and the valves, to say nothing of the burning and cutting away of the packing in the stuffing boxes, but in the Serpollet boiler the heat is very much greater. The steam is what is termed super-heated, being brought into contact with very highly-heated metal, so that if a double acting engine with the ordinary slide valves were used it would last for a comparatively short time. But in gas engines the temperature is very much higher than in any steam engine, at the moment of explosion the gases are at a white heat; this great temperature is far above what is ever reached in a steam engine, but M. Serpollet, to avoid the inconvenience of the superheated steam, designed his engine on gas-engine lines, using four single-acting cylinders and mushroom valves, as in gas engines.
A Serpollet engine, as used in the small cars, is shown in fig. 43, which is a side view and section. The cylinders, four in number, are 1 15/16in. diameter and 2 13/16in. stroke, two cylinders being in front and two behind the crankshaft, the cranks being at right angles to one another. The valve shown in section on the left-hand side of the drawing is a steam inlet valve, the exhaust valve being beyond it, and not shown in the drawing. The exhaust passes out through the round port just above the piston, and through the nozzle shown below the cylinder, it must be understood there are separate inlet and exhaust valves to each cylinder, or eight valves in all. These valves are worked by cams on the upper shaft, which gears with the crankshaft. By shifting this shaft to the right or left the two different sets of cams for going ahead or backing are brought into use.
The valves are kept closed by the pressure of the steam, aided by the spiral springs on their spindles. The crankshaft runs in oil.
A skeleton drawing of the Serpollet steam carriage is shown in fig 44. The frame is made of channel steel; a cast steel frame (not shown in the drawing) carries the engines A. B is the instantaneous steam generator in an asbestos-lined casing. It consists of a series of tubes, through which the water is forced and turned to steam. The tubes have a total length of about 150ft. Those nearest the fire are thicker, and have a clear bore of 4 mm. or .157in. Those in the upper part are 5 mm. bore or .196in. C is one of the chimneys, with an opening both up and down. To prevent the products of combustion being carried to those riding in the car when running with the wind, a curved sheet iron screen D is fixed above the chimney opening. E is the casing containing the burners, which are of the Swedish type, sometimes known as the Primus. F is the paraffin oil tank, for it must be understood that the fuel is lamp oil, not benzoline or petrol. An air pump G under the driver’s seat pumps air into the oil tank, putting a pressure on the burners. H is the water tank. J is the handle for the pump for forcing water into the generator to start the engine. K is a safety or relief valve; it differs from the ordinary safety valve in that the pressure of the steam opens a valve, which allows water, not steam, to escape from the steam generator. At L are three pressure gauges – one shows the pressure of steam, which varies according to the road; another shows the pressure in the burners; a third, generally fixed in front, gives the pressure in oil tank. The burners are fed by a small pump. M is the steering handle. At N are two quadrants with racks - one is for reversing the engine; the other alters the stroke of the oil and feed pumps. These two pumps work together from one crosshead, and by altering the stroke of the pumps the speed of the vehicle is regulated more or less, oil and water being pumped in equal proportions to the burners and boiler. O is a series of pipes for condensing the exhaust steam. Before the steam reaches the condenser it passes through a separator or filter P, which separates the oil from the steam, thus preventing oil being carried into the water tank, and from thence to the boiler. R is one of the radius bars to resist the strain on the chain. S and T are treadles - one works a band brake on the axle; the other works the throttle valve for regulating the pace of travelling. U is the brake handle operating on the tyre of the road wheels.
These small cars take about seven or eight minutes to start from cold. They are very comfortable to ride in, but in the writer’s opinion require more care and attention in driving than most petrol cars. How long the generators will last is an unknown quantity, as there are so few Serpollets in England. Their manufacture has been taken up by the British Power, Traction, and Lighting Co., Ltd., York, who will probably considerably simplify the machinery, and make it more in accordance with English ideas.
The working pressure on the road is from fifteen to twenty-five kilogs. per square centimetre, equal to 198 lbs. to 340 lbs. per square inch, according to the directions of the maker.
The wheels, which have pneumatic tyres, are 32in. and 28in. diameter; the wheelbase is 4ft. 11in.
The engine is geared to the road wheels by one chain (the axle being a live one), as eight to twenty-five, that is, in the car shown in the photograph.
The Serpollet is extremely quiet in running, and if it could be somewhat simplified it would probably be one of the best cars on the road.*
• Since the above was written the writer has seen something more of the running of a Serpollet car. The car seems easy to manage, and is extremely comfortable to ride in; the speed up hill is good, and the owner reports that it really gives no trouble.