Saturday, March 3, 2012

Motive-Power Inventions


An Explosion Pump

Although the idea of an explosion pump is not new, the Humphrey pump, invented in 1906, is not only novel but forms a complete revolution in the methods of raising large quantities of water. So great is the novelty that when the inventor (Herbert A. Humphrey) read his first paper on the subject to the Institution of Mechanical Engineers, London, Professor C. Vernon Boys said he had felt from the beginning very much in the position of the undergraduate to whom a coach had explained the principle of the siphon. After listening with admiration, the undergraduate said, "Yes, sir, but will it really work?" The author's pump was one of those things which, had he (Professor Boys) had the good fortune to think of it, he would have had some doubt in trying, because he would hardly have believed that it would really work in the most beautiful way in which the author had shown that it actually did.

The outstanding novelty in the Humphrey pump is that it has no piston and no connecting-rod. A column of the water itself acts as the piston. The general arrangement is not unlike a large U tube, the one leg of which is closed at the top to form an explosion chamber above the surface of the water in the tube, the space above the water in the second leg being perfectly free. An explosion of a gaseous mixture in the confined space in the first leg will force the water down that leg and up the other one. We may imagine some of the water overflowing at the free end, and the remainder falling back in the tube and rising again in the first leg. In doing so it will compress the waste gases resulting from the explosion, and when the column of water has expended its kinetic energy, the compressed gas will react and force the column of water to rise again in the second leg; the column of water would behave like a pendulum until its energy was dissipated.

To convert such an arrangement into a pump, we should require some inlet of water into the U tube, an escape for the exploded gases, an automatic inlet of a fresh explosive mixture, and an automatic ignition apparatus.

The accompanying diagram shows the general principle of the Humphrey pump. The inlet of the water is obtained through a simple water valve box, so arranged that the static pressure of the column of water in the discharge pipe keeps the water valves closed. When the column of water makes its forward swing under the pressure of the explosion, the water-pressure upon the valve box will be withdrawn, the level in the pump pipe will fall below that in the supply tank, and water will flow from the supply tank to follow the moving column of water, and also to rise up into the explosion chamber, to fill the partial vacuum produced by the gases having expanded beyond atmospheric pressure. There will also be a tendency for the water to rise to the level of the supply tank. It may be observed in passing that this gives a convenient means of controlling the amount of water to be permitted to enter the pump at each stroke. If the level of the water in the supply tank be raised, there will be a corresponding increase in the amount of water admitted, and so on.

Suppose there has been an explosion, forcing the great column of water forward and up the water-tower. At a point some distance below the water-level in the tower the outlet pipe branches off. Of course, the water might be made to discharge as an overflow at the top of the tower, but then its flow would be spasmodic, being only on the forward or upward stroke, whereas with the arrangement just described there will be a continuous flow, as water will enter the outlet pipe on the downward as well as the upward stroke. As soon as the column of water commences to travel backwards, the static pressure of the water will close the valves of the supply tank.



At the forward motion of the great water piston, resulting from the explosion, the exhaust valve is mechanically released and falls by its own weight. The waste gases are therefore expelled by the backward rush of the water, until the water reaches the exhaust valve itself and closes it by impact. The exhaust valve is placed at a lower level than the top of the explosion chamber, in order that some of the gases will be entrapped in the head of the chamber and will act as a compression cushion.

If this gaseous cushion were composed entirely of waste gases, they would detract somewhat from the efficiency of the next explosion. The explosion chamber is therefore provided with a scavenger valve, through which fresh air is drawn in, so that the compression cushion is composed chiefly of air.

When the compression of this air cushion has taken up the energy of the great water pendulum, the compressed air forces the water forward once more. It is not the exhaust valve which opens this time, for a sliding-lever having moved below a collar on the valve spindle, locks it and prevents it falling, as was the case at the first stroke. The other end of this sliding-lever has released the inlet valve for the explosive mixture, so that the second forward stroke of the water piston draws in a fresh charge of gas and air.

The second return or backward stroke of the water piston compresses the explosive mixture, and also operates a small piston which controls the ignition apparatus. This is so arranged that at the moment the compression has reached its maximum and the reaction has commenced, electrical contact is made and the mixture is fired by an electric spark.

On the long outward stroke of the water piston, resulting from the explosion, we have the opening of the exhaust valve and the scavenger valve; the spent gases are expanded beyond atmospheric pressure and fresh air is drawn in. Then follows the long return stroke, the backward swing of the water piston, which expels the waste gases, closes the exhaust valve, and compresses the air cushion in the head of the explosion chamber.

The pressure of the rising water in this long return stroke operates a relay which moves the interlocking rod in one direction, locking the scavenger and exhaust valves, and unlocking the gas valve. This leaves the gas valve free to act, against a supporting spring, on the second outward stroke of the water piston.

The pressure of the rising water in the second or short return stroke causes the relay to move the interlocking lever in the opposite direction, so that the gas valve is locked while the scavenger and exhaust valves are unlocked, and left ready to act on the next forward stroke. This simple see-saw motion locks and unlocks the two sets of valves alternately.

Public attention was directed to this invention when King George, accompanied by the Queen, performed the opening ceremony of the new pumping station at Chingford. This station was to raise 180,000,000 gallons of water every twenty-four hours, from the River Lea to a large reservoir some twenty-five to thirty feet above the level of the river at that point.

The Metropolitan Water Board had found this a serious problem to face, as the cost of pumping so large a quantity of water was going to prove excessive. While they had the problem before them, H. A. Humphrey happened to read his paper before the Institution of Mechanical Engineers, and his Pump and Power Company were invited to put forward a tender for the large pumping station. When the different tenders were opened, it was found that the Humphrey Pumping Station would cost £19,000 less than the lowest offer for a steam-driven centrifugal pumping plant. Further, the cost of fuel for the steam plant was two or three times more than the consumption estimated for the explosion pumps.

So far no explosion pump had been made greater than 35 horse-power, whereas at Chingford there were to be four pumps, each developing between 200 and 300 horse-power, and a fifth pump of about half that power. There was, therefore, little practical data to go upon; and in order to safeguard the interests of the Board, the condition upon which the inventor's tender would be accepted was a penalty of £20,000 in case of failure. The inventor was not only willing to give this guarantee, but also accepted the condition that if his consumption of fuel exceeded the 1.1 lb. of anthracite estimated to produce one horse-power, he was to pay a penalty of £1000 for every one-tenth of a pound exceeding the estimated amount.

There was a delay of nearly one year in getting this pumping station ready for work, and in some quarters a suspicion arose that the new invention was not working out on a large scale in the manner predicted by the inventor; but the whole delay was due to the Water Board not having been able to get the buildings for the pumps ready earlier owing to pressure of other work. So carefully was all designed that the only detail altered, as the result of seeing the huge pumps at work, was the substitution on certain valve spindles of a solid nut instead of the split one originally provided. Fortunately the pumps proved a complete success, and instead of penalties there was nothing but praise.

The speed of this pumping engine will, of course, be controlled by the swing of the great water pendulum, and that again will be dependent upon the length of the column of water, which may be altered at will by altering the length of the discharge pipe. Other things being constant, the period of oscillation is almost proportional to the square root of the length. With the diameter of the discharge pipe (which may be described also as the play pipe) 2 feet, the maximum velocity of flow permitted 14 feet per second, the length of pipe 50 feet, there will be 31 cycles per minute. By doubling the length of pipe, the number of cycles is nearly halved, being 14.3 per minute. The length of play pipe usually adopted is from 60 to 80 feet. The diameter of the play pipes in the Chingford plant is 7 feet.

The starting and stopping of the pumps is very simple. If the pump is at work and it is desired to stop it, all that is necessary is to switch off the electric current which operates the sparking coil. The water piston will come to rest with a fresh charge of gas and air in the explosion chamber, and the mere switching on of the electric current will ignite this and start the water piston once more. If desired, the pumps may be controlled from a distance.

In starting the pump up for the first time, all that is necessary is to use compressed air with the gas, and so depress the water level a little below the usual charge volume. If the exhaust valve is then forcibly opened, the water will rise in the chamber and compress the explosive mixture, and all is ready for the switching on of the electric current.

At the meeting of the Institution of Mechanical Engineers, when the inventor read his paper upon explosion pumps, Professor C. V. Boys said that perhaps the most surprising part of the pump or engine, as compared with any other machine yet made, was the fact that, when all was cold and at rest, one touch of the button instantaneously started the machine going at full speed. No other engine was in any respect like that.

It is evident that there can be no rotary governors to control the inlet valve, but a throttle valve may be controlled by the pressure or height of the water, and either the mixture or the gas alone may be governed according to the power developed. On the other hand, the pump may be allowed to work at maximum capacity, and a float on the high-level tank may serve to cut off the ignition and switch it on again as the water rises and falls between two fixed levels.

Without going into further detail, it may be mentioned that while the pump described is a four-cycle pump (two outward and two inward strokes in each complete cycle), it is quite convenient to construct a two-cycle pump, and that this may be done without the aid of outside pumps to draw in the gas and air and to force them into the explosion chamber, as has to be done in the two-cycle gas engines.

It may be mentioned also that the Humphrey pumps can be converted into high-lift pumps by means of air vessels fitted with valves being added at the end of the discharge pipe. A small air vessel is placed at the entrance to the large air vessel into which the high-pressure water is to be delivered. The inlet into the large air vessel is fitted with a non-return valve, which remains closed until the inrush of water into the small air vessel has compressed the air therein sufficient to open the valve. The energy of the water column is then spent in delivering water in the larger vessel, and any backflow from it is prevented by the valve closing. This would leave the water-pendulum without sufficient potential energy to compress the next combustible charge on the return stroke, but there is sufficient energy in the compressed air in the small air vessel to make good this deficiency.

The inventor does not believe that his internal combustion pump will be confined to pumping water from one level to another; he is confident that there is a very wide field of operation. He is not alone in that belief, for at the meeting of the Institution of Mechanical Engineers, already mentioned, Professor Henry J. Spooner said, "If the internal combustion pump proves in the future to be a successful competitor of the gas engine for power purposes, then it is probable that one of the most useful fields for its employment will be found in the propulsion of ships. Quite apart from the possibility of driving a turbine attached to a screw-propeller, there is the jet-propeller, which is the most efficient of all propellers for ships if properly constructed and operated. What has been lacking so far has been a type of pump capable of delivering very large quantities of water at comparatively low heads, and it is just these conditions which suit the author's pumps in their simplest form." The inventor does not have visions of jet-propelled Atlantic greyhounds, as this system of propulsion is not suitable where high speed is essential.

Of course the field for the invention as a prime mover would be unlimited, and although there would be a loss of about twenty percent due to the introduction of the water turbine, the inventor has a good deal to spare in the way of cost, while the column of water which takes the place of the piston, the flywheel, and the connecting-rod, requires no lubrication and has no working parts to go out of order.

Another field open to the explosion pump is the compression of air, and the inventor suggests in this connection that blast-furnace gas might be used in an explosion pump, which could take the place of the blowing-engines for producing the blast.

In closing his remarks in the discussion at the meeting of Mechanical Engineers, Professor C. V. Boys said in a playful manner that he had wondered to a certain extent how it was that the inventor had been inspired. No doubt the members had their own theories on the question, but personally he had wondered whether the inventor, when he had seen large pipes lying about in the Mond gas stations, which were not just then required for the purpose of conveying gas, had quietly put them on end, without being seen, and converted them into a big telescope, and had discovered the physical cause of water travelling at the rate of two miles an hour in the canals of Mars, as had been observed by Dr Lowell. It was quite clear that the water in the canals of Mars could not travel at the speed of two miles an hour in virtue of any other physical cause than by the aid of such a pump as the inventor' s. If he had observed this, he was still the inventor from the English Patent Office point of view; he was the first importer of the invention on this Earth.

Knight 'Valveless' Motor

The invention of what has been called a 'valveless' motor was made by Charles F. Knight, of Chicago, about 1908. It is not really valveless, but it has no valves of the orthodox make. The supply and exhaust pipes are opened and closed by means of two concentric sleeves, with slots in them. The sleeves slide up and down between the piston and the cylinder walls, movement being given to them by connecting-rods, whose lower ends are operated by eccentrics carried on a small shaft. The eccentric shaft is driven positively, by a silent chain, from the main shaft, and rotates at one-half the speed of the motor.

It is not difficult to picture the operation of these two sleeves, each going through a definite cycle of movements under the control of its eccentric. When the piston is at its top centre, and is starting downward on its inlet stroke, the inner sleeve is at the lowest point of its travel, and is commencing to move upward. In this position its slot, in moving upward, is commencing to uncover the opening of the inlet. The outer sleeve is about midway in its downward travel, and its slot has commenced also to uncover the inlet. As the sleeves are moving in opposite directions to one another, the one slot is uncovering only the bottom of the inlet opening, while the other is uncovering only the top, so that the whole inlet is still completely covered by some part of each sleeve. But as the one eccentric pushes the inner sleeve upward, while the other eccentric pulls the outer sleeve downward, there comes a time when both slots are exactly opposite the inlet, and a supply of the gaseous mixture from the carburetor enters the cylinder. At this point the piston is a little more than half-way down on the suction stroke, so the gases are drawn in. The outer sleeve has reached its lowest travel, and is moving very slowly, but the inner sleeve is moving rapidly and the inlet is quickly closed. During this time the exhaust outlet has been closed by the combined sleeves.

While the piston is making its compression stroke, the inner sleeve continues to move upward; the inlet and exhaust are, of course, closed while the explosion occurs. When the piston is about two-thirds of the way down on the explosion stroke, the exhaust outlet commences to open. The inner sleeve is moving downward, and as it goes its slot will uncover the exhaust, the outer sleeve being practically stationary at the top of its stroke, with its slot almost right opposite the outlet. As the outer sleeve starts on its downward move, and gaining in speed as the inner sleeve loses, the exhaust is first uncovered and then closed by the time the piston has completed its upward exhaust stroke. The timing of the sleeves by means of the eccentrics is ingenious, and may be altered by varying the 'lead' between the eccentrics and by properly locating the slots in the sleeves. By the time the eccentrics have gone through a complete cycle of operations, the crank has turned twice, giving the four cycles (suction, compression, explosion, and exhaust).

In a motor in which the piston has a 5 1/2-inch stroke, the travel of the sleeves is only 1 1/2 inch, hence the movement of the sleeves is leisurely compared to the fast-moving piston, which has to make two of its longer strokes to one of the short strokes of the sleeves. The efficiency of this motor is very high.

Valveless Gas-Engines

In a paper read before the Iron and Steel Institute, at Leeds, October 2, 1912, Alan E. C. Chorlton described his invention of a valveless gas-engine. It has the appearance of a triple-expansion steam-engine; but what appears to be one of the cylinders is the ordinary air and gas pump arrangement. The other two cylinders are in reality one double or 'duplex' cylinder, for they are connected at the top and at the bottom. There are no valves, the one power piston itself acting as the inlet valve, and the second power piston acting as the outlet valve.

The casting of the cylinder is of the very simplest type, consisting of two single-walled U tubes placed end to end, the inlet and the exhaust ports being about the joint; flanges on the cylinders—set back somewhat from this juncture—hold in between them the exhaust and inlet boxes. The absence of joints and cavities in the combustion chamber reduces the risks of pre-ignition, and improves the efficiency of scavenging. The piston operating the inlet port has, of course, a slight lead on the piston operating the exhaust port, so that the latter is closed at the time of explosion. Every stroke is a driving stroke.

The duplex cylinder is placed in a simple tank of water for cooling, and it is possible to run the engine with this water boiling. With this type of engine it is quite practicable to have a single unit of 10,000 brake-horse-power.

Gnome Rotary Engine

The advent of the Gnome Rotary Engine, in 1909, marked a revolution in aviation. The novelty of the invention consisted in making the cylinders themselves rotate around the crank-shaft. Instead of the orthodox revolving crank-shaft and fixed cylinders, there was a fixed crank-shaft and revolving cylinders, the object being to keep them cool.

The inventor was Mons. Seguin (France), and so revolutionary was the idea that it met with very severe criticism at first. Even when it had proved its remarkable staying powers, an expert said (1912): "If I were asked to give my opinion of the Gnome motor in as few words as possible, I should say that it was theoretically one of the worst-designed motors imaginable, and practically the most reliable aeroplane engine I know of. I should have to add as a qualification that I assume it receives the constant attention of expert mechanics." (Earl L. Ovington. Scientific American, cvii., No. 11.)

The object in the Gnome motor is to obtain as much power as possible with a minimum of weight; the real purpose being a fast flyer for exhibition purposes, not for long distance travel. Every part of the engine is cut from the solid metal, or from a forging; no part is cast. The metal from which the cylinder is cut weighs 81 lb., but the finished cylinder which is cut out of this weighs only 4.5 lb. The exhaust valve screws into the end of the cylinder, and is arranged so that it may be removed in one piece with its seat, as it requires constant grinding. Indeed, after about fifteen hours running, the motor is taken to pieces and thoroughly overhauled, while the valves are re-ground and re-timed, and new valve-springs inserted.

The bore of the cylinder has a mirror-like surface, and there are no piston-rings, each cylinder merely having an 'obturateur,' which is a simple ring of thin sheet bronze. The crank case is cut from a solid forging, weighing in the rough 116 lb., while all that remains in the finished crank-case is 13.5 lb. It seems strange that of the total weight of metal prepared for the cylinder and crank-case, less than 10 percent remains in the finished motor, 90 percent being waste shavings. The object of the Gnome's revolving cylinders is, as already stated, to keep them cool, water-cooling not being convenient in an aeroplane.

Sun-Power Plant

One of the most interesting of the practical attempts which have been made to utilize the radiant energy of the sun, is that which was invented by Frank Shuman, of Philadelphia, a few years ago.

Instead of focusing the rays of the sun by means of lenses and mirrors, and using the concentrated rays to heat a boiler, Shuman collects the radiations falling upon a very large surface area. A large plant which was to be shipped for use in Egypt was fitted up in Philadelphia for experimental work, prior to shipment. It consisted of twenty-six long troughs, made of wood, each containing a flat metal honeycomb water vessel, covered with two layers of glass, having a one-inch air space between them. In order to prevent loss of heat through the box, the under surface was insulated by a two-inch layer of granulated cork and two layers of waterproof card-board.

In order to collect as much radiation as possible, plane mirrors were mounted on two sides of the boxes, and the rays were reflected upon the surface of the water vessel. By this means, an absorptive area of over ten thousand feet was secured. The boxes were supported on stands about thirty inches off the ground, and were placed with their surfaces perpendicular to the sun at the meridian, the position being readjusted about every three hours.

The water vessels were connected at one end by a feed-pipe from the water supply, and at the other end to a steam-pipe. The branch pipes from the various units led into a main steam-pipe which conveyed the steam to the engine.

The prime-mover is specially designed for low pressure, and has a condenser and other usual auxiliaries. The water from the condenser is pumped back into the absorber, thus making a continuous circuit, the only water loss being accidental leakage.

During the experiments in Philadelphia, the plant was used to pump 3000 gallons of water per minute, to a height of thirty-three feet. The experience gained by these trials led to a number of important alterations being made before the plant was shipped to Egypt. Instead of using plane mirrors to reflect the rays through the glass tops of the water vessels, rectangular zinc troughs were placed in the focus of long parabolic mirrors, each about 200 feet in length. These parabolic mirrors of silvered glass were mounted in arc-shaped frames, which could be turned so as to face the sun at all times. This alteration of position was accomplished automatically, the power being obtained from the engine itself, which is provided with a pair of friction pulleys under the control of a special thermostatic regulator.

When the plant was erected in Egypt, the temperature of the tank reached a point so near the boiling-point of zinc, that the metal could not withstand the heat. But the results obtained were so encouraging that the inventor decided to replace the zinc troughs by steel ones. It will be understood that there is only a film of water kept passing through the troughs. The inventor claims that the cost of running his Sun-power plant is only one-third of that from an ordinary coal-heated steam plant.

It is interesting to note in connection with this invention that Sir J. J. Thomson, in his presidential address to the British Association in 1909, said: "How great is the supply (of energy) the sun lavishes upon us becomes clear when we consider that the heat received by the earth under a high sun and a clear sky is equivalent, according to the measurements of Langley, to about 7000 horse-power per acre. Though our engineers have not yet discovered how to utilize this enormous supply of power, they will, I have not the slightest doubt, ultimately succeed in doing so; and when coal is exhausted and our water-power inadequate, it may be that this is the source from which we shall derive the energy necessary for the world's work. When that comes about, our centres of industrial activity may perhaps be transferred to the burning deserts of the Sahara, and the value of land determined by its suitability for the reception of traps to catch sunbeams."

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