190 NEW DEVELOPMENTS IN HIGH VACUUM APPARATUS. 



saturated at the temperature of the circulating water. The same is also true with respect to 

 the rotative dry vacuum pump, in which the vapors are saturated at the temperature of the 

 jacket water (which is the same as the entering circulating water). This important char- 

 acteristic of the rotative dry vacuum pump, as well as the gasometer system referred to as 

 existing in the New York Edison Company, is described in a paper presented in, 1913 to the 

 National Edison Companies. 



Where a steam ejector carrying 2 inches absolute in service received the vapors cooled 

 to, say, 90 degrees, the hydraulic vacuum or rotative dry vacuum pump would handle vapors 

 cooled to or saturated at 70 degrees which would occupy approximately only 46 per cent of the 

 volume of the vapors going to the steam ejector, so that the steam ejector does 3.16 times 

 as much work as it would if its vapors were cooled to the same temperature. 



Nothing has been stated in this paper with regard to the mechanical efficiency of the 

 ejector, but, before closing, I would like to call attention to the fact that at a recent con- 

 vention superiority of the steam ejector was claimed because all the heat is saved, includ- 

 ing that equivalent to the work performed. In reply figures were submitted showing that 

 the amount of useful work performed by the steam ejector represented in British thermal 

 units only .003 of 1 per cent of the total evaporative heat of the steam delivered to the main 

 turbine. This also gives some index of the efificiency of the steam ejector. 



The; author states that the steam required by the non-condensing ejector will be reduced 

 30 to 40 per cent by the condensing ejector. The Worthington ejector tests show a reduc- 

 tion of approximately 50 per cent; had the author given actual steam^ consumptions, then a 

 study of the heat balance could be made. It is not necessary to pump the circulating water 

 through an inner condenser and thus waste the heat. On the contrary, the condensate is 

 pumped through this condenser on the way to the open (or closed) heater, thus saving this 

 heat, and recent installations have been called for where an after-surface condenser as well 

 as inner-condenser is required in order to save recharging to the feed with air which oc- 

 curs when the ejector discharges into an open heater. The condenser offered for this ser- 

 vice combined both the inter-condenser and after-condenser in one shell. 



It will be found that the percentage of steam saved by using the condensing type of 

 ejector is a very large factor and not to be argued down without a careful study of the heat 

 balance. It should be remembered, however, that the heat balance on a ship is very differ- 

 ent from that in stationary plants, where frequently the auxiliary exhaust steam to be util- 

 ized must be limited to an amount which will not raise the feed to more than 120 or 130° 

 P., the feed being further raised by being passed through economizers and other heat- 

 reclaiming devices. The statement is made that the amount of air absorbed by the feed water, 

 when the ejector is used, is 35 per cent of that when the twin-beam air pump is used. The 

 twin-beam air pump has been practically superseded in the latest installations by the twinplex 

 or wet and dry pirnip. It is not believed that actual tests will show any increases over the 

 ejector in the air absorption by the feed. This, however, would be to some extent modified 

 by the design of heater and whether the exhaust passed into the body of the feed or 

 through a falling spray. 



The layouts accompanying the paper show a very complicated system with special regu- 

 lating devices and elaborated heater and filter tank which must all be taken into acco'unt in 

 connection with both the weight and space occupied, and where the heat balance requires 

 a condensing ejector, both the weight and space are also effected and the twinplex system 

 will be found much the simplest and most advisable. 



