CHAPTER XVII 



Pumping Machinery The Scoop Wheel The Archimedean Screw The Reciprocating Pump 

 Types Valves Theory of Action Air Vessels Positive Rotary Pump. 



ART. 156. PUMPS. 



MOST hydraulic prime movers are, with slight modifications, capable of 

 being reversed, and when driven by an external agency provide a means 

 of raising water from a lower to a higher level. 



Thus the overshot water wheel corresponds to the chain and bucket 

 pump ; the breast or Sagebien wheel to the scoop wheel ; the reversed 

 pressure turbine gives the centrifugal pump, and the reversed recipro- 

 cating engine the reciprocating pump. The capacity of each of these 

 machines as a prime mover also to a large extent indicates its capacity, 

 when reversed, as a pump, and just as the reciprocating engine and 

 turbine are the most important types of prime mover, so the reciprocating 

 piston pump and the centrifugal pump are the most important types of 

 pump. 



In addition to those already mentioned, we have a series of special 

 types of pump, each of which is specially adapted to some particular 

 combination of circumstances. Of these, the Archimedean screw, the 

 jet pump, the positive rotary pump, the hydraulic ram, and the air lift 

 pump, are interesting examples and will be considered in due course. 



ART. 157. THE SCOOP WHEEL. 



This has in the past been largely applied to the drainage of fen 

 districts, and simply consists of a Sagebien wheel reversed and driven 

 usually by steam power, the water then being lifted in the buckets from 

 the lower to the higher level. It is fitted for lifts up to about 6 feet and 

 may be constructed to deliver up to about 400 tons per minute, giving an 

 efficiency under favourable conditions of upwards of 75 per cent. Its 

 chief advantages appear in cases where a large quantity of debris is 

 encountered. As in the Sagebien wheel, the inclination of the floats 

 should be such as to prevent shock at entrance and losses at exit as far 

 as possible. It is found that the best results are obtained when the 

 angles which the vanes make with the water surface at entrance an<7 



