NEW DEVELOPMENTS IN HIGH VACUUM APPARATUS. 183 



According to the opinion of numerous marine operating- engineers, simplicity 

 is of greater practical value than the saving of a few pounds of live steam. 



Until the appearance on the market of the steam-air ejector the twin-beam air 

 pump quite monopolized the field. Therefore it will be interesting to compare the 

 two types. 



Considering first the comparative steam consumptions based on equal air and 

 condensate handling capacity it will be found that the steam consumption of the 

 air ejector, plus that of a turbine-driven condensate pump, is lower than that of the 

 twin-beam air pump, even if the latter is arranged with a dry and a wet cylinder. 



The weight and space requirements are also decisively in favor of the air ejec- 

 tor outfit. Plate yy illustrates a set of either type of equal air and condensate 

 handling capacity, and Table I gives the relative weight, cubical space and floor 

 space. 



Table I. 



Weight. Cubical space. Floor space. 



Twin-beam air pump 14,500 lbs. 375 cu. ft. 33 sq. ft. 



Two air ejectors and one condensate pump. . 2,100 lbs. 18 cu. ft. 8 sq. ft. 



Other comparative advantages of the air ejector are : — 



It has no moving parts nor valves, does not require lubrication, nor attendance 

 during operation. 



Its operation is noiseless, simple and reliable. 



No foundations are required and no restriction as to location exists. It is to 

 all intents and purposes a piece of pipe. 



Since there are no moving parts there is no wear, and consequently the mainte- 

 nance costs are practically nil. 



When using a steam-air ejector the feed water carries less absorbed air into 

 the boilers than when using a twin-beam pump. The condensate pump forms a self- 

 contained unit. All the attention it requires is to see that its ring oiling bearings 

 are kept filled with oil. The discharge head of the condensate pump is not limited, 

 as is the case with the twin-beam air pump. Since it operates independently from 

 the air ejector the pump has greater flexibility and can easily take care of large 

 amounts of condensate without influencing the air-handling capacity. This is not 

 possible with the twin-beam air pump, in which the air-handling capacity is limited 

 by the piston speed and simultaneously by the amount of condensate removed. 



When using air ejectors and condensate pumps a considerable saving in weight 

 and cost of piping can be made because the pipe sizes are smaller, as much higher 

 velocities are permissible when dealing with water and air separately. 



Steam-air ejectors are generally supplied in pairs for marine condenser instal- 

 lations, this subdivision having the advantage of reducing the steam consumption 

 by operating with one under light loads or when the installation is air-tight, also of 

 providing additional capacity in case of unexpected leakage. In larger installations 



