PUMPING MACHINERY OF THE WATER AND SEWERAGE HOARD XXIX. 



Following this was the pump recently erected at Ryde, 

 but which was imported in 1903, hence lacking the more 

 recent improvements, the period of four years from 1903 to 

 1907 having been the most remarkable in the introduction 

 of such improvements in the history of this class of 

 machinery. During this time steam consumption has been 

 reduced from 36 lbs. to say 22 lbs. per HP. per hour. Hence 

 a considerable gain will accrue to more modern install- 

 ations. As an instance of what can be done in America, 

 they have produced a five series, side by side, centrifugal 

 pump, the capacity of which equals thirteen million gallons 

 per day to a head of 430 feet. 



The question of the size and position of the air vessel on 

 suction and delivery pipes is one which is intimately con- 

 nected with the success or failure of a pumping plant aud 

 it is always best to err on the side of large capacity than 

 to run the risk of a deficiency in these auxiliaries to effective 

 working. Constructors of centrifugal pumps appear to 

 have treated the question of end-thrust in a lax manner, 

 some even going so far as to state that it does not exist, 

 nevertheless they make some provision by the addition of 

 thrust rings on the impeller shaft generally quite inadequate 

 for the requirements ; when the pumps are electrically 

 driven, some makers depend upon what they term magnetic 

 pull to counteract thrust, but such provision fails, especially 

 during that period necessary to charge the pump and rising 

 main, as it will be readily understood that until a constant 

 load is on the pump variable conditions prevail as regards 

 the power absorbed by it. The only safe provision is thrust 

 surface large enough to provide for this which need not add 

 to the friction, it being so adjusted that at constant load 

 it would be virtually inoperative. Many appliances such 

 as ball race, friction rings and ordinary marine type thrust 

 blocks have been used, but none, in the author's opinion. 



