Air compressor

“ It is evident that an air compressor which has the steam cylinder and the air cylinder on a single straight rod will apply the power in the most direct manner, and will involve the simplest mechanics in the construction of its parts. ”

“ Compressed air for starting and injection is generally supplied by a three stage air compressor or a compressor in which the pressure is built up in three different steps, the second cylinder taking the air from the discharge of the first, and the third cylinder taking the air from the second, and compressing it to about 250 pounds above the compression pressure of the engine. ”

“ But air is a poor conductor; it acquires heat faster than it can give it off to the water surrounding the cylinders. In compound air compressors the air compressed in one cylinder is cooled before being passed on to the next cylinder, where it is further compressed. The heat loss in compressing air in a single stage up to 100 pounds gauge pressure is about 30 per cent. Air that enters a compressor at the normal pressure of the atmosphere and with an initial temperature of 60 degrees F., if not cooled will become heated to 415 pounds gauge pressure. ”

“ The capacity of each compressor is 230 cubic feet.
MAIN LINE, PIPING AND WIRING FOR BLOCK AND INTERLOCKING SYSTEM, SHOWING JUNCTION BOX ON COLUMN
The motor-driven air compressors [Pg 142] are controlled by a governor which responds to a variation of air pressure of five pounds or less. When the pressure has reached a predetermined point the machine is stopped and the supply of cooling water shut off. When the pressure has fallen a given amount, the machine is started light, and when at full speed the load is thrown on and the cooling water circulation reëstablished. ”

“ FIG. 18.—HYDRAULIC AIR COMPRESSOR.
The illustration shows the general type of this compressor, though it has been subject to much modification in different places. In America, a plunger is used instead of a piston, and as it always moves in water the result is more satisfactory. The piston, or plunger, moves horizontally in the lower part of a U shaped cylinder. Water at all times surrounds the piston, and fills alternately the upper chambers. The free air is admitted through a valve on the side of each column and is discharged through the top. ”

“ The best practice in America has brought this heat loss down to 3.6 per cent. (old Ingersoll Injection Air Compressor) , while in Europe the heat loss has been reduced to 1.6 per cent. Steam-driven air compressors are usually run at a piston speed of about 350 feet per minute, or from 60-80 revolutions per minute of compressors of average sizes, say 18" diameter of cylinder. Sixty revolutions per minute is equal to 120 strokes, or two strokes per second. ”

“ With compound air cylinders the air is compressed to alternate stages of pressure in the different cylinders, and the clearance loss is thus reduced because of the reduced density of the air in the clearance spaces. In ordinary practice air compressors deliver the air at less than 100 pounds pressure, so that with a properly designed air cylinder the clearance space is so small that the capacity of the compressor is not materially affected. ”

“ One such two-cycle motor that has been designed especially for automobile use employs a separate air compressor driven by the engine itself and used as the clutch and variable speed transmission of the car. The amount of pressure generated in the compressor is dependent upon the resistance offered to its operation—or, in other words, it increases with additional load carried by the motor. The compression, or compressed air, rather, is carried directly from the compressor to the cylinders of the motor, being admitted at the proper time by a rotary valve driven by the crank shaft. ”

“ As already referred to, the elimination of the air compressor constitutes the chief improvement embodied in the Vickers type of engine, seeing that the greatest worry which the Diesel engineer has had to encounter has been this very compressor. Needless to remark, therefore, this feature alone strongly recommends the new system to the experienced man. Further, the power required to drive the compressor above-mentioned is considerable, so that economy is not one of the least results due to its absence. ”

“ For cleaning electric generators and motors by blast, these machines have many advantages, and on account of the large volume of air handled they are much to be preferred to the small-volume high pressure jet of the ordinary air compressor often used for this purpose. With the portable turbo-blower there is no danger of damage to the insulation through high pressure, or through the carrying of moisture and oil into the windings with the air jet. ”

“ The heat generated by compression in the cylinder, C, is absorbed by a spray of water from the pump, H, the vapor being carried along with the air through the pipe, R, to the chamber, Y, where it is separated, and falling to the bottom is circulated, as just described, by the pump, J. X is a small auxiliary air compressor, to obtain the necessary compression to start the engine, and is worked from the boiler, W. In future engines this compressor will be superseded by a specially designed injector, which will produce the necessary pressure at a considerable reduction in cost. ”

“ When the compressor is unloaded, it is evident that the function of the air piston is merely to force the compressed air through the discharge valves and passages from one end to the other until more compressed air is required, this being indicated by a fall in the receiver pressure. ”

“ A familiar form of air compressor is the hand pump used for inflating bicycle tires. This simple device illustrates two important facts; first, that a considerable amount of energy must be used to overcome the expansive force of the air, and, second, that part of the energy applied to the pump produces heat. That the heat thus produced and dissipated27 in the surrounding air represents a loss of energy is apparent; but energy is wasted in another way that is, perhaps, not so evident. When a gas is heated its expansive force is increased. ”

“ The gas compressor is worked by a water motor, hot air or gas engine; a low pressure water motor may be efficiently driven by water from the main, but with large installations it is more economical to drive the compressor by a gas engine. To overcome the intermittent flow of gas caused by the stroke of the engine, a regulator on the floating bell principle is placed after the compressor; the pressure of gas in the apparatus governs automatically the flow of gas to the engine. ”

“ If the compressor is situated in such a position that most of the heat of compression is delivered at the jet, there is little to be gained by reheating. In most cases, however, the air has returned to normal temperature by the time it reaches the point where it is to be used, and, if a suitable air heater is installed at this point, the volume may be increased greatly by a comparatively small expenditure. ”

“ An air compressor reversed in direction is an air exhauster, such as we find carrying money in department stores. The powerful in-draft of this apparatus, often drawing large pieces of paper or card into the pipes, has led to the invention of a means of removing dust and dirt, admirable in thoroughness. A receiver, shaped to suit its special task, is passed over pictures and their frames, upholstery, carpets or bare floors, and through the flexible pipe attached to its handle, dust and dirt are borne into a reservoir where they are caught by water for due removal. ”

“ It is difficult to equalize power and resistance in air compressors with long strokes. The speed will be jerky, and when slow, the fly wheel rather retards than assists in the work of compression. This action tends to derange the parts and makes large bearings a necessity. The piston in a long-stroke compressor travels through considerable space before the pressure reaches a point where the discharge valve opens, and after reaching that point it has to go on still further against a prolonged uniform resistance. ”

“ The new air compressor herewith illustrated may be operated by steam or water power, and is available for work in mines, tunnels, or quarries, for driving rock drills, coal cutters, and hauling and pumping engines, working mining pumps, for use in factories, and in fact for all service where a safe and efficient power is required. The construction of the machine, the capacity of which differs according to the amount of power required, will readily be understood from the illustration. ”

“ For small installations, single-stage reciprocating machines, driven directly by steam engines or by electric motors are, no doubt, the most suitable. In the case of large plants, using the air continuously in a number of air jets, where the load factor is high, it is certainly more important to install a two or three-stage compressor, owing to the greater economy of working. The larger capital expenditure will be compensated by the considerable saving of energy. As compared with single-stage compression to 100 lbs. gauge pressure, a saving of 20 per cent. ”

“ It has been used as an air compressor, exhauster and also for receiving the exhaust from a steam engine, taking the place, in that case of both condenser and air pump.
The injector is not an economical device, but it is simple and convenient; it occupies a very small space, is not expensive and entirely free from severe strains on its durability; moreover, where a number of boilers are used in one establishment, it is very convenient to have the feeding arrangements separate, so that each boiler may be a complete generating system in itself and independent of its neighbors. ”

“ It is economical to combine the pressure [Pg 85] and suction systems by arranging the air compressor to draw air from the vacuum receiver into the compressor cylinders whence it is returned to the pressure line.
Automatic valves keep the pressures in the pressure and vacuum sides of the system within pre-determined limits. “Make up” air is admitted by the automatic opening of an atmospheric valve when the pressure side of the system is low and the vacuum side high, so that the pump is deprived of sufficient air to operate the system efficiently. ”

“ INGERSOLL-SERGEANT DUPLEX STEAM-DRIVEN AIR COMPRESSOR.
One of the advantages of air-driven machines under ground is that the exhaust furnishes fresh air to the miners and cools the atmosphere. The result has been that in metal mines, where there are no noxious gases escaping from the ground, the exhaust from the air-drills, together with the natural air currents, has supplied sufficient ventilation. In the coal mines, however, it has been necessary to employ other means. ”

“ A modification of the reciprocating pump was manufactured by the Sanitary Devices Manufacturing Company in which [145] light-weight poppet valves placed in the heads of the cylinder were used, as indicated in Fig. 79. Curves of the watts per cubic foot and efficiency of this type of compressor are shown in Fig. 80. It will be noted that this compressor shows a better efficiency than the air compressor at all degrees of vacuum and it is the best reciprocating pump that the writer has ever tested. ”

“ These check valves lift alternately, and cushion on water; and as the compressed air is forced into the pipe connecting with the receiver, without a possibility of any of it escaping back into the receiving chambers, it is claimed that there is the smallest possible loss of power, and that the machine will give fully 90 per cent of steam power expended in the shape of compressed air. The compressor is compact in form, strongly made, simple in construction, and not liable to get out of order. ”

“ Now, if the piston, instead of being loaded by weights, be connected to the piston rod of a steam engine, or by means of a connecting rod to a crank (which is rotated by a belt or some other driving mechanism, and the valves be operated automatically, as the valves on a water pump) , the simple apparatus is converted into a perfect air compressor, which really is nothing else than an air pump, and the air can be pumped into the receiver against a high pressure the same as water is forced into an elevated reservoir by a pump. ”

“ At B the air-compressor o delivers its compressed air to the tank k, from which it flows to the sending apparatus n, and thence through the tube g back to station A. Upon its arrival at A it passes through the receiving apparatus and enters the tank e, which is open to the atmosphere at h. The tanks d and k serve as separators to remove from the air any dirt and oil coming from the compressors, and they form a cushion, deadening, to some extent, the pulsations of the compressors and making the current of air in the tubes more steady and uniform. ”

“ Several years ago it was impossible to find a temperature controller which operated without compressed air that would hold the temperature closer than a variation of 10 degrees, which is too wide a variation for catsup pasteurization. The compressed air controllers worked very well but required an air compressor where the pressure must be held within certain limits, and air pipes to connect with all the controllers. ”

“ It is obvious that cost of construction and maintenance have much to do with the commercial value of an air compressor. The hydraulic piston machine not only costs a great deal more in proportion to the power it produces, but it costs more to maintain it, and it costs more to run it. ”

“ It was a great advance in steam engine design when the single cylinder of Watt was replaced by two or more cylinders, using steam at high instead of low pressure. Thus apportioned in a series of cylinders the steam is not nearly as much cooled, with loss of working power, as when but one cylinder is used. So likewise, it is best to divide the compressing of air into two or more stages, so that at each stage the air may be cooled, and thus more easily compressed than if a single operation completed the business. The best air compressor is virtually the converse of a steam engine. ”