Steam Jets. The James Brady Foundry Co. (Chicago, U.S.A.) state, in their Bulletin on this subject, that the special steam jet elbows are usually placed at the top and bottom of a vertical riser. The jet of steam from the nozzle enters the elbow directly in front of, and parallel to, the face of a special wearing liner. This prevents or reduces the wear on the liners, as the jet protects the liners from the pounding action of the ash. A renewable sectional liner is provided of specially hard metal at all points in which the material makes actual contact with the pipe or fittings. These liners are interchangeable in all elbows, and each individual liner can be turned end for end when affected by wear.
In cases where the length of horizontal run exceeds 125 ft. it is necessary to supplement the primary nozzles by “booster” steam jets to maintain the velocity of the air current.
Buffer Boxes. At the discharge end of the pipe line it is necessary to insert a baffle or buffer box to take the impact of the ashes, and thus prevent wear on certain parts that are not designed to stand up to the destructive effects of the impact. The function of the box is to bring the ashes to rest, so that they may fall by gravity into the ash tank or on to the storage pile. When delivering into a tank it is very essential to install a buffer box, as otherwise the velocity with which the ashes enter the tank will pack them so tightly that they will not discharge automatically through the valve or gate. The location of the ash hopper can be wherever most convenient for loading the vans, railway trucks, or barges, etc., but preference should be given to a site which makes possible a pipe run with a minimum number of bends.
One American firm of engineers, the Vacuum Ash and Soot Conveyor Co., New York, have done away with the numerous steam jets and the blowing effect produced thereby, and rely entirely on suction by using a sealed ash tank and exhausting the container and pipe system by means of a single steam jet injector built into the roof of the ash tank, and discharging its steam directly into the air.
By this means it is claimed that the following advantages are obtained: (1) No sand-blast effect, such as is inevitable when blowing at high velocity. (2) No steam enters the ash tank and consequently there are no condensation troubles. (3) Much less dust is blown into the atmosphere as the steam is never in contact with the dust. (4) Conveyor pipes are cleaner since no steam enters them, as in “blowing,” and there is therefore no condensation, caking and corrosion.
FOOTNOTES:
[1] Inst. Mechanical Engineers Journal, March, 1920, p. 291.
CHAPTER VIII
MISCELLANEOUS APPLICATIONS OF PNEUMATIC CONVEYING
Pneumatic Despatch Tubes. The ordinary pneumatic conveyor picks up material at one point and unloads it at another and continues this course consistently, whereas the “pneumatic despatch tube” is a conveyor of small articles enclosed in a special cartridge which is built to fit the tube and which travels to and fro as required, carrying a variety of articles, or if necessary, the same articles, backwards and forwards between the same two stations or a series of fixed stations.
The despatch tube thus constitutes an effective “mechanical messenger.” One or more tubes are run between the points to be connected, with a despatch and receiving terminal at each end, or if necessary, a single line to operate in both directions can be designed. The tubes vary from 1½ ins. to 4 ins. diameter, and they are also made of oval sections up to 4 ins. × 7 ins.; rectangular tubes have been installed in special installations, chiefly in telephone exchanges for convenience in dealing with certain cards there employed.