Fig. 24 represents a line of two stations with an air-compressor at each station. Such an arrangement is proposed for the line of postal tubes over the New York and Brooklyn bridge, or for any two stations located a very long distance apart, say six or eight miles.
Fig. 24.
DIAGRAM OF A TWO-STATION, TWO-COMPRESSOR LINE.
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Referring to the diagram, we have at station A an air-compressor, c, which draws its supply of air from the tank e, and delivers it, compressed to the necessary pressure, into the tank d. From the tank d the air flows to the sending apparatus, a, and thence through the tube f to the station B. Upon arrival at B it flows through the receiving apparatus m, and then by the pipe l to the tank j. A second air-compressor, o, is located at station B, and it draws its supply of air from the tank j. The tank j has an opening to the atmosphere, i, through which air can enter when the air-compressor draws more than is supplied from the pipe l. The opening i in the tank j serves as an escape for air when the air-compressor at station A is started before that at station B. Stations A and B are similar in their arrangements. 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. The tanks e and j form traps to catch any moisture, oil, or dirt coming out of the tubes.
Carriers are placed in the tubes and despatched by means of the sending apparatus a and n. They are received from the tubes and delivered on to tables by means of the receiving apparatus b and m. It will be seen that the arrangement is such that the air flows through one tube and returns through the other, the same air being used over and over again. Any air that escapes at the sending and receiving apparatus is replaced by an equal amount entering the tanks e and j from the atmosphere. By thus keeping the same air circulating in the tubes we prevent an accumulation of moisture in the tubes.
The air is at its maximum pressure in the tanks d and k. The pressure falls gradually as it flows along the tubes and is down to atmospheric when it enters the tanks e and j. The pressure at the receivers, b and m, is just sufficient to push the carriers out on to the tables. The construction of the sending and receiving apparatus will be described in another place.
Fig. 25.
DIAGRAM OF A TWO-STATION, ONE-COMPRESSOR LINE.
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