196 NEW DEVELOPMENTS IN HIGH VACUUM APPARATUS. 



capacity, under identical operating conditions, have given the following results : Twin-beam 

 pump with cooler, 1,465 pounds ; air ejector, 935 pounds. 



In regard to his remark that twin-beam air pumps generally are operated at from one- 

 third to one-half of their normal speed, it would have been very interesting to have some 

 shipbuilder or marine engineer comment on that point. My experience with twin-beam 

 pumps or twinplex pumps has been somewhat limited, but reports from operating marine 

 engineers do not coincide with Mr. Katzenstein's remark. 



It is perhaps unnecessary to reply to the numerous remarks made by Mr. Katzenstein 

 in regard to stationary plants, because this Society consists of marine engineers, and I do 

 not think you are interested in proceedings which have no connection with marine engi- 

 neering. 



As to his statement that the rotative drive vacuumi pump is in a position to handle vapor 

 at a considerably lower temperature than an air ejector, I cannot agree with the same. If 

 Mr. Katzenstein's assumption that the vapors are cooled inside the cylinder by the jacket 

 water were true, the air pump will have to remove at each stroke a certain amount of water. 

 Every one knows very well that the dry vacuum pumps have very close clearances, and if 

 there is water in the cylinder, which is not compressible, something else will have tO' give way, 

 viz., the cylinder head or the piston. 



As far as the mechanical efficiency of the steam air ejector is concerned, it is known 

 that this efficiency is low, as is the case with all dry-air pumps. But the mechanical efficiency 

 is not of such great importance as the thermal efficiency, since the latter influences the fuel 

 consumption. The thennal efficiency of the air ejector is as high as 98 per cent. All the 

 heat which enters with the live steam is returned directly to the feed water, with only a very 

 small amount of loss, consisting of loss through radiation in the steam pipes and the appa- 

 ratus itself. 



Referring to Mr. Katzenstein's remarks in regard to inter-stage and after-condensers, 

 the use of the condensate for circulating water purposes necessitates the arrangement of a 

 number of complicated automatic appliances, as operating conditions vary. It also requires 

 a rather complicated piping arrangement. For these reasons inter-condenser air ejectors do 

 not appeal to marine engineers, and in over 600 ships with air ejectors there is not one with 

 inter-stage condensers. 



The figures given in Table I refer to the up-to-date twinplex air pump and were ob- 

 tained from the manufacturer of this pump. They are based on equal air and condensate 

 handling capacity; that is to say, both pumps removing the same amount of condensate in 

 pounds per hour, and also the same amount of air in pounds per hour, under equal operating 

 conditions. 



Mr. Katzenstein also said that weight and space requirements are not of prime impor- 

 tance in cargO' vessels. I leave it tO' the marine engineers to pass judgment on the correctness 

 of this statement. Mr. Smith has already confirmed the statement that weight and space re- 

 quirements are of considerable importance. 



Mr. Katzenstein also mentioned that in some marine installations air ejectors had been 

 applied, but always in connection with twin-ibeam air pumps. It is true that there have been 

 several installations where the air ejector was used in connection with a twin-beam air pump. 

 The request for making those installations was based on the fact that the necessary vacuum 

 could not be obtained with the twin-beam air pump, and the air ejector was installed to 

 improve the vacuum. The twin-beam air pump was used only for taking out the condensate 

 from the condenser, and in that case was run at about one-third of the normal speed. 



