A similar machine of more crude design is used for whitewashing walls of stables, cattle pens, etc. All these plants comprise an air compressor, either power or hand operated, from which the air is led to a special injector which draws up through a second pipe a certain amount of the material to be sprayed. The paint or other material is then atomized and impelled with considerable force on to the surface to be covered.
The sand blast is another application of pneumatic conveying in which the medium conveyed is sand, which has well-known cutting and erosive effects when it impinges on a surface at high velocity. This plant is used for decorating glassware, obscuring sheet glass, and also for cleaning stone buildings by the actual removal of the face of the previously discoloured stone.
The pneumatic conveyance of energy is exemplified by rock drills, riveting machines, coal-cutters and innumerable other portable tools. Energy is expended in compressing air which is transmitted through pipes and made to yield its stored energy by driving the air motors of the tools or other apparatus in question.
Conclusion. Enough has been said to show that pneumatic conveying has made great progress, and that the possibilities of this method of dealing with the moving of solid materials are much greater than has been generally recognized.
Almost anything that will enter a pipe up to about 9 ins. diameter can be conveyed in this way, either by “blowing” or “suction” or by the “induction” method.
Weight and size is an advantage rather than otherwise, and bricks can be dealt with more successfully than flour. The writer’s experience, in the results of actual working with pneumatic conveying, indicates that no problem should be considered too difficult to be tackled by this method, and that even the most unlikely materials can be conveyed successfully by pneumatic means.
BIBLIOGRAPHY
Readers wishing to amplify their knowledge of pneumatic conveying may find useful the following references—
“Pneumatic Dispatch,” by H. R. Kemp, M.I.C.E., M.I.E.E., M.R.M. Paper before the Inst. of Post Office Engineers. October, 1909.
“Power Plant for Pneumatic Tubes in the Post Office,” by A. B. Eason, M.A., A.M.I.E.E. Paper before the Inst. of Post Office Engineers. 18th October, 1913.