96 The Drainage of Fens and Low Lands, 



centrifugal pumps are not required, the peculiar form of the 

 pump casing acting in the place of such plates, consequently 

 the friction of the disc A is reduced. The whole of the disc 

 and arms are steel in one casting. The spindle passes 

 through two stuffing-boxes cast on the casing E, to which are 

 fitted gun-metal glands. A driving pulley is attached to the 

 end of the spindle. Valves are placed at the bottom of the 

 suction pipe to retain water when the pump is not at work. 

 The area of the disc is equal to the area of the inlet and 

 outlet pipes at all points. As these pumps, when working at 

 their best speed, discharge every revolution three times the 

 cubical contents of the disc, the discharge passages are three 

 times the cubical capacity of the disc. By a simple arrange- 

 ment the discharge pipe from the pump is made to act as a 

 condenser for the steam from the engines. These pumps have 

 been further improved in detail since the publication of the 

 above description. 



The points essential to a good pump, and common to all 

 makers, are as follows : — The shape of the vanes to be such as 

 to facilitate the movement of the water so that it shall enter 

 and leave without shock, and shall therefore correspond as 

 nearly as practicable with the path described by any fillet of 

 it from the interior to the exterior of the fan ; all changes of 

 direction in the connections with the pump to be as gradual 

 as possible, and all enlargements or contractions in the 

 passages avoided ; the passages throughout to be proportioned 

 so as to have a gradually increasing velocity in the water until 

 it arrives at the circumference of the fan, and then to have a 

 gradually decreasing velocity until it issues from the discharge 

 pipe ; ample space to be allowed in the case, the larger the 

 opening in the case the better the water passing off. 



The chief attempts of makers to improve this form of pump 

 have been in the form of the blades. AH agree that these 

 must be curved The form of the curve varies with the ideas 

 of the different makers. At the trial at the Exhibition of 



