624 



HYDRAULICS AND ITS APPLICATIONS 



Here the curve D' K B L B', etc., formed by adding the ordinates of the 

 two single velocity curves ABC, A' B' C', etc., gives the velocity of the 

 combined discharge, without air vessel. The area A E G F represents 

 the discharge per revolution, and each of the sectioned areas represents to- 

 the same scale the volume entering and leaving the air vessel per cycle. 



These areas may ba calculated or measured by planimeter. The 

 following table gives the proportion of the whole discharge per revolution 

 which enters and leaves the air vessel per cycle. 



For satisfactory working the volume of the delivery air vessel should 

 be from forty to sixty times the volume of water entering it per cycle, 

 this proportion increasing with the speed of rotation and the length of 

 delivery pipe. 



On the suction side the volume should be from ten to thirty times the 

 volume entering per cycle, this proportion also increasing with the speed 

 and with the length of suction pipe. 



To Summarise. An air vessel on the suction side of a pump reduces the ; 

 maximum acceleration and the range of velocities in the supply pipe, an< 

 thus, besides reducing friction losses, reduces the fluctuations of pressui 

 in the suction chamber, and therefore the liability to water hammer 01 

 separation. The steadying effect becomes more pronounced as A , a, l s 

 increased and less pronounced as a s is increased. The larger the volui 

 of the chamber . the greater is its effect, an increase of sectional ai 



