Compressed air; theory and computations . he delivery ratio relative to atmospherewill be 9 or a gage pressure about 120 lb. This would be accom-plished without compounding and without development of any-more heat than without the booster. However, more workwould be required of the reciprocating engines. Hence, instudying such an improvement the designer should determinewhether the engines can meet the demand for increased volume of air delivered by and the efficiency of centrifugaland turbo compressors, fans and blowers are matters understoodby but few, seldom known, and often far f
Compressed air; theory and computations . he delivery ratio relative to atmospherewill be 9 or a gage pressure about 120 lb. This would be accom-plished without compounding and without development of any-more heat than without the booster. However, more workwould be required of the reciprocating engines. Hence, instudying such an improvement the designer should determinewhether the engines can meet the demand for increased volume of air delivered by and the efficiency of centrifugaland turbo compressors, fans and blowers are matters understoodby but few, seldom known, and often far from what is assumed orclaimed. The theory underlying these subjects is somewhatdifficult and is deferred to Chapters VIII and IX. CHAPTER VSPECIAL APPLICATIONS OF COMPRESSED AIR In this chapter attention is given only to those applications ofcompressed air that involve technicalities—with which the de-signer or user may not be familiar, or by the discussion of whichmisuse of compressed air may be discouraged and a proper Fig. 12. Art. 35. The Return-air System.—In the effort to economize inthe use of compressed air by working it expansively in a cylinderthe designer meets two difficulties: first, the machine is muchenlarged when proportioned for expansion; second, it is consider-ably more complicated; and third, unless reheating is applied theexpansion is limited by danger of freezing. To avoid these difficulties it has been proposed to use the air at SPECIAL APPLICATIONS OF COMPRESSED AIR 69 a high initial pressure, apply it in the engine without expansion,and exhaust it into a pipe, returning it to the intake of the com-pressor with say half of its initial pressure remaining. Thediagram, Fig. 12, will assist in comprehending the system. To illustrate the operation and theoretic advantages of thesystem assume the compressor to discharge air at 200 lb. pressureand receive it back at 100 lb. Then the ratio of compression isonly 2 and yet the effective pressur
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