Pneumatics

“ This is applicable to the water closet refuse alone. The pneumatic system acts as follows: A large air-tight cylinder on wheels, or, what answers equally, a series of air-tight barrels connected together by tubes about 3 in. diameter, placed on a cart, brought as near to the cesspit as is convenient; a tube of about the same diameter is led from them to the cesspit; the air is then exhausted in the barrels or cylinder either by means of an air pump or by means of steam injected into it, which, on condensation, forms a vacuum ”

“ A steady gradually diminishing pressure is exerted against the piston by these heated gases, and drive it to the upper end of the cylinder. The exhaust-valve then being opened by the mechanism of the engine, the piston descends by atmospheric pressure, forcing the gases out into the air. While the power-piston is making its downward stroke the supply-piston draws in a fresh charge of air, which is forced into the furnace during the up-stroke. A fly-wheel makes the motion of the engine smooth and uniform. ”

“ Air compressed in an accumulator or reservoir is employed to give motion to multiplying pulleys or an air engine.
Expansion of liquids, other than water (by heat) , into the gaseous form. Engines in which the fuel is burnt under pressure and the total products of combustion employed (with or without steam) to drive a motor.
Steam is in reality one of the last-mentioned sources of power; it is employed by direct pressure on a piston or ram (see Section 32) ; or to produce direct rotary motion (see Section 75) ; also in the jet pump, No. 801; or injector (see Section 45) ”

“ Air under pressure increases in density and heat, and exerts an increased power in every direction. Hence compressed air is applied in locomotives; and its power is employed in many machine-plants, such as those of mines and water-works. An air-compressor or air-pump is a cylinder fitted with a piston and rod, and with valves at which the free air may enter and with others at which the compressed air may be applied, together with the needful connections of this apparatus with the driving power. ”

“ The suction nozzle through which the material enters the system, together with the “free air” which is to act as the conveying medium.
Pumps and Exhausters. The type of apparatus used for creating the flow of air varies according to the ideas of the numerous makers of the plants. It must be remembered that for a pump working under the conditions required for pneumatic plants it is not a high vacuum that is required; the most [Pg 11] important function is to handle very large quantities of air at a comparatively low vacuum. ”

“ In speed, in comfort, in saving the mechanism from pronounced concussion, and in facility of steering, there is no question as to the superiority of the air chamber as compared with solid rubber. The curious fact, moreover, remains that in the very circumstances which emphasise the weak points of the pneumatic tyre the solid would be even worse. High speed and a heavy car form a combination which tests the pneumatic tyre severely, but the solid tyre in like circumstances can with difficulty be kept on the wheel at all. At high speed, again, the pneumatic tyre is particularly liable to puncture ”

“ The reasons why pneumatic methods for elevating and conveying are now receiving such attention are to be found in the advantages of pneumatic over mechanical conveying. These may be summarized as follows: Economy in labour; flexibility of plant both in design and operation; elimination of dust and its harmful effects on the employees; and in many instances the recovery of dust which is valuable and which would otherwise represent a serious financial loss. Wear and tear on moving parts is reduced to a minimum. ”

“ Heavy commercial systems in which the fan is replaced by a reciprocating exhauster, producing currents of air suitable for conveying such materials as coal, ashes, sugar, leather tanning bark, ores, granite chippings, wood blocks, oranges, etc., which it would be impossible, or undesirable, to pass through a fan.
(3) Induction System. A compressed air injector is used to produce a partial vacuum on the suction or inlet end of the pipe system, and to produce a pressure above atmospheric at the delivery end, thus avoiding the necessity for a discharger. ”

“ There are two methods of circulating the water through the cylinder jackets and radiator. The most common method consists of the introduction of a pump in the lower portion of the circulating system. In the case of automobile motors, this pump is driven by gears connected with the crank shaft of the engine. Such a pump will be either of the gear or centrifugal type, and will suck the cooled water from the lower portion of the radiator, and force it through the jackets. ”

“ Pressure Method.—Supplementing the splash, and frequently used as the sole mean is the plan adopted by many, and known as the pressure system, which not only lubricates the bearings and cylinders, but also the other mechanism in the car, is the use of pressure, which may be exerted by gravity, or by the use of hand pumps.
Some employ the exhaust of the engine to draw up the oil. This requires ducts leading to all the parts which are adapted to take a liquid lubricant. ”

“ It is necessary here to mention that all pneumatic conveying is not done by exhausting, but frequently by the use of pressure, that is, that the air is not sucked along the transport line but is actually blown in under pressure by fans, air compressors, or rotary blowers, according to the circumstances. ”

“ As the pressure cannot exist until the engine is running, a hand air pump is usually provided, by which a sufficient pressure may be produced in the tank to force out enough gasoline for starting. It is necessary to use as long a pressure pipe as possible, in order to prevent the possibility of flame passing through it to the supply of fuel, a long pipe, exposed to the air, cooling the gases to such an extent that they cannot ignite the gasoline. ”

“ It is naturally not so rapid as circulation that is forced by a pump, and more liable to become inoperative by the clogging of the pipes, jacket, or radiator.
Of the methods of increasing the surface of a cylinder in order to cool it by a blast of air, the most usual is to cast it with flanges that project from all parts of the combustion space. These become heated as the temperature of the [Pg 35] cylinder walls increases, and the air that is blown against them carries off the heat. ”

“ As soon as 95 water gas gauge pressure has entered this box, the diaphragm rises and closes the valve, which does not re-open until the lights are turned on, when it admits gas at the same rate at which it is consumed at the burners. Each jet can be regulated to a given size, so that it cannot blaze and cause waste, and all the lights in a carriage can be turned off or half-off, by a key at the end of the carriage. Finally, each carriage has a pressure gauge to indicate the pressure of gas in the cylinders, and to shew when the supply is exhausted. ”

“ For low speeds, solid tires give good results in traction and the absorption of jolts from small obstacles, but for anything above six or eight miles an hour, pneumatic tires are a necessity in preventing the rapid shaking to pieces of the mechanism. A hard tire touches the ground at but one point, and its grip on the road will be much less than that of a pneumatic tire which, being slightly flattened by the weight it bears, presents an oval or elliptical surface to the road. ”

“ When a train is running, uniform air pressure exists throughout its length--that is to say, the main reservoir on the engine, the pipe from end to end of train, the triple valves and supplementary reservoirs on each vehicle, are all charged ready for work, the brake cylinders being empty and the brakes off. The essential principle of the system is, that maintaining the pressure keeps the brakes off, but letting the air escape from the brake pipe, purposely or accidentally, instantly applies them. ”

“ Air-lift Pumping. The air-lift pump is a common means of conveying by pneumatic means [Pg 96] and should not be confused with the above methods of raising water by compressed air.
In the air-lift method of pumping air under pressure is admitted at the foot of a pipe already submerged in the well. The air does not merely bubble through the water, as might be supposed, but passes up the pipe as a mixture of air and water. ”

“ P is a steam-driven air-pump on the engine, which compresses air into a reservoir, A, situated below the engine or tender, and maintains a [Pg 196] pressure of from 80 to 90 lbs. per square inch. A three-way cock, C, puts the train pipe into communication with A or the open air at the wish of the driver. Under each coach is a triple-valve, T, an auxiliary reservoir, B, and a brake cylinder, D. The triple-valve is the most noteworthy feature of the whole system. ”

“ Because of the cycle of events on which its operation depends, the piston must be forced to perform the inlet and compression strokes before pressure can be developed, and it is necessary to revolve the crank shaft by outside means until a charge of mixture has been taken into the cylinder, compressed, and ignited, when the engine begins to work by the pressure from the combustion, and takes up its cycle. ”

“ In the electro-pneumatic system a full-size semaphore is used. Compressed air, from pumps situated at intervals of 10 to 20 m., is conveyed along the line in an iron pipe, and is supplied to a cylinder at each signal, exactly as in pneumatic interlocking, before described. The rail circuit, when complete, maintains pressure in a cylinder, holding the signal " off." On the entrance of a train or the failure of the current, the air is liberated and the signal arm is carried by gravity to the " stop " position. ”

“ In the four-cycle type of engine, which is in almost universal use for automobiles, the events are considered with reference to the movement made by the piston during which they are performed, and may be called the inlet, compression-combustion, power, and exhaust strokes. In order that the engine may continue to run, it is obvious that the events must be performed in the correct order, and that the failure of one will affect all the others. ”

“ The valve gear on the gas compressing cylinder is arranged so that no gas is delivered to the inlet valves of the working cylinder until the air cylinder has provided sufficient air to insure perfect scavenging of the products of combustion, this preventing the fuel from becoming contaminated with the burnt gas. Speed regulation for varying loads is effected by shifting the valve gear of the gas pump so that the gas is delivered at an earlier or later period in the stroke of the working piston, thus causing a variation in the quantity of gas delivered to the working cylinder. ”

“ SYSTEMS AND APPLICATIONS OF PNEUMATIC CONVEYING Conveying by mechanical means has existed for many centuries, and is one of the earliest forms of man’s ingenuity towards labour saving as we know it to-day. The pneumatic conveyance of materials from one position to another, either horizontally or vertically, is the most recent form of automatic handling of solid substances. ”

“ The need of water for human consumption and for irrigation purposes caused the ancient inventor to carry out nearly all his experiments with that substance, and the first instance we have of anything approaching pneumatic conveying is the well known injector in which steam is passed through one pipe, placed at right angles to a second pipe, at such a velocity as to reduce the pressure in the second pipe to below the atmospheric pressure. ”

“ But in the two-cycle Diesel type of engine, the high pressure of the pure air is used for scavenging, and as this is admitted with so large an initial force, the exhaust port may remain uncovered for a longer period than would be the case were the air to rely entirely on the up-stroke of the piston for its compression. ”

“ The heat due to road friction, the pressure arising from the weight of the car, and the combination of centrifugal force with the weight of the tyre itself—much greater than that of a pneumatic—all create expansion and make the tyre rise from its bed and at times fly off bodily. A tendency to creep in the rim is also caused by the non-absorbent qualities of the solid as compared with the pneumatic tyre. ”

“ Some of the streets of our large cities are so filled with water- and gas-pipes, electrical conduits, sewers, steam-pipes, etc., etc., that it is almost impossible to find space for pneumatic tubes, especially of large diameter. Railway or water facilities have much to do with the location of a central pumping station, on account of the coal supply. ”

“ The pneumatic system requires a pump, an air-tight tank, and pipes to the various outlets. The water pumped into the air-tight tank will occupy part of the space generally occupied by the air. The air cannot escape and is, therefore, compressed. ”

“ Compressed air is used in starting the engine, which is admitted to the cylinder through an auxiliary valve which is operated by a starting cam on the cam shaft. By this mechanism, high pressure air is furnished to the cylinder during a portion of the working stroke, turning it over on the first few revolutions as a common air engine. As soon as the engine picks up speed, the starting valves are thrown out of operation, and the engine proceeds on its regular working cycle with the oil fuel. ”