FOR AUXILIARY PURPOSES ON BOARD SHIP. 159 



ducted under the most favorable circumstances as to the condition of the working 

 parts of the simplex pump. 



"Reciprocating pumps decrease steadily in efficiency due to wear, while the 

 centrifugal pump will probably change very little in this respect. Further, the 

 centrifugal pump being of the experimental type, certain slight mechanical changes 

 will doubtless improve its efficiency" (pp. 1227, 1228). 



The results of the tests carried out at Annapolis are shown in curves, 

 Plate 80, compared with various tests on reciprocating types of pumps. These 

 curves show up more favorably for the turbine-driven unit than would be inferred 

 from the quotations in the report. 



That the tests were satisfactory, however, is demonstrated by the fact that 

 turbine-driven boiler-feed pumps are now being built for installation, as follows : — 



One of the main advantages of the centrifugal boiler feed pumps is that they 

 deliver a uniform pressure and volume at a given speed, eliminating entirely the 

 vibration in the unit and piping caused by shock in reciprocating pumps. Further- 

 more, the pressure being kept constant, a much lower margin of pressure difference 

 between the pump pressure and boiler pressure is obtained than with reciprocating 

 pumps. 



The ease with which a small turbine can be started up and the absence of 

 danger due to water hammer have opened up a large field for the small turbine 

 for ballast pumps on board passenger vessels. The necessity for making ship 

 quickly on this type of boat is of the utmost importance. The ballast pumps on board 

 the Hendrick Hudson were guaranteed to start from rest and be under full load in 30 

 seconds. Actual tests showed that this duty could be accomplished inside of 20 sec- 

 onds without danger to any part of the machine or piping. 



For boiler-feed pump purposes the advantage of regulating the o'^eration of 

 the pump by the pressure at the discharge has obvious advantages. Th(: majority 

 of pumps installed for boiler-feed purposes in central stations nov/ are fitted with 

 some type of pressure regulator with the main speed governor sr, adjusted that it 

 acts merely as an emergency governor. Considerable saving in steam consumption 

 can be effected by the adoption of a pressure regulator, as will be seen by the curves 

 shown in Plate 80 showing the effect of pressure regulation on the total water con- 

 sumption. This is particularly applicable to marine work where t^ie demand on the 

 boilers is a constantly varying quantity during maneuvers. 



In addition to the use of turbine-driven main condenser and l^oiler-feed pumps 

 the small turbine is being quite generally used for driving aux-jijary pumps on 

 vessels of large power. In this class of work there is very little difference in the 

 marine application from that of similar use on land. 



Turbine-driven ash-ejector pumps have been supplied many s'hjps by Stone of 

 London for both merchant and war vessels, but in this country,^ as far as the 

 writers know, the only turbine ash ejectors are on the older battleships and two 

 colliers. The turbine is eminently satisfactory in this service, ^is steam can be 

 turned on without warming up and full delivery head obtained aim ost instantly. 



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