VOLUTE CHAMBER 



B just before reaching this pipe. The velocity of whirl in this 

 will thus vary from A to B, and can only at one particular section correspond 

 with that at discharge. The result is, that practically the whole of the 

 kinetic energy at discharge is dissipated in shock and eddy production. 



This may be avoided to a certain extent by designing the chamber so 

 as to have a sectional area which increases uniformly from A to B, a 

 cutwater being placed as shown at A (Fig. 302), so as to ensure the whole 

 flow being at once discharged from the chamber. 1 This is termed a volute 

 chamber and is usually so designed as to give a uniform velocity of whirl in 

 the chamber, equal to about '4 times the velocity of whirl on leaving the 

 impeller. 



Here again, however, the velocity of whirl on leaving the wheel is always 

 much greater than that of flow in the volute, so that there is still a loss 



FIG. 302. 



by shock due to the impact of the high velocity water leaving the vanes, 

 on the more slowly moving water in the volute chamber. 



Practically the efficiency of the chamber as usually designed is very 

 low, experiments by Dr. Stanton 2 indicating that it often does not exceed 

 about 10 per cent., and that the volute chamber in itself is only slightly 

 more efficient than the concentric chamber. 3 



1 This cutwater, if designed so as almost to touch the impeller, tends to cause considerable 

 vibration when the pump is working. Generally the working is found to improve, and the 

 efficiency not to suffer unduly, by the provision of a generous amount of clearance at this point. 



2 " Proceedings Institute Mechanical Engineers," 1903 (p. 715). 



3 When correctly designed, the chamber, however, is capable of converting some 60 per 

 cent, of the kinetic energy of discharge into pressure energy. For a rational design of such 

 chambers a paper to be read by the Author before the Institution of Mechanical Engineers 

 during the session 1912-13 should be consulted. 



