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Equipment Used Afloat, Ashore New Type of Rotary Pump Is Efficient—Designed With gee HE striking difference between theory and practice is nowhere more aptly shown than in the — development of the present day faulty and inefficient rotary pump from the high ideal of theoretical design. As most engineers know, rotary pumps are not new, and the number of those now on the market possessed of limited rotational speed, low suction lift and small endurance, is large. The fault may lie, in all probability, not in the inherent difficulties of con- structing ideal apparatus out of stub- born and oft-times intractable raw materials, but rather in not holding that construction to a_ sufficiently high ideal. Paradoxical as this may seem, it is essentially true. The mechanical engineer who stops to compromise, has lost his battle. And the difficulties in the way of efficient rotary pump design have been great enough to cause many an engineer to compro- mise. What are the essential qualifica- tions of the ideal rotary pump? As- suming an all-purpose pump, these six factors suggest themselves: 1, Ability to operate at high rota- tional speeds without noise or vibration. 2. Ability to pump equally well re- gardless of direction of rotation. 3. Freedom from the necessity of internal lubrication. 4. Freedom from packing troubles. 5. Good suction lift (say 20 feet or more). The author is connected with the American Machine &' Foundry Co., Brooklyn, N. Y aS KT TESS mai) ZZ Nl FIG. 2—DIAGRAMMATIC VIEWS OF THE BY FRANCIS JURASCHEK FIG. 1—GENERAL VIEW OF A NEW 2%4-INCH, 83-GALLON-PER-MINUTE ROTARY PUMP DIRECT CONNECTED TO A COMMERCIAL HIGH-SPEED MOTOR 6. Life of several years under ad- verse conditions. A brief examination of these points reveals the weakness of the ordinary run of rotary pumps. High speed operation is desirable not only be- cause of the greater capacity devel- oped in comparison with a low speed pump of ‘equal size and weight, but also because of the avoidance of speed reducing devices when the pump is driven by a commercial high speed motor. Size for size, and consequently cost for cost (for both the initial cost and the operating cost of a pump are governed by the size) the high speed pump is immensely superior to the low speed pump. But the direct-connection of a ro- tary pump to a standard electric motor, and the successful operation of such a unit, introduces many tech- nical difficulties before which designers SECTION- A-B AND FOUNDRY CO. 29 have quailed. The high rotational speed of such a motor, about 1800 revolu- tions per minute, calls for the unusual and the unique in rotary pump design. There must be static and dynamic balance of a high order, and free running fit of part to moving part. Any engineer who has tried out the usual rotary pump, designed for op- eration at 400 to 600 revolutions per minute, directly connected to an elect- ric motor, will have vivid recollec- tions of the results. Great racket, destructive vibration, opened clear- ances, heated bearings, and almost total loss of volumetric and mechan- ical efficiences, occur regularly. Regarding the ability of the ideal rotary pump to pump equally well regardless of the direction of rotation, it would seem obvious that this must follow as the natural result of any (Continued on Page 60) oS] | SSS rd mer) : iil alll ee OU IN | \ A Z Za\ il ue IN INNA LLL -————] % Gi N WN PARTITION Ly NEW 2%4-INCH, 83-GALLON-PER-MINUTE ROTARY PUMP OF THE AMERICAN MACHINE