234 



HYDKAULICS AND ITS APPLICATIONS 



elasticity of the pipe as a whole, or to an increase in the time occupied in 

 bringing the moving column to rest. Owing to this, and to the viscosity 

 of the water, the motion gradually dies out. 



The state of affairs is then as indicated in Fig. 107, of which A 

 represents a diagram from behind the valve, and B from a point 15 feet 

 from the open end of the pipe line experimented on by the author. In 



. 1 



Press. 



At, 



Static. 

 Atmos. 



Press . 

 Press . 



FIG. 107 



this case the valve was closed in *07 seconds, and the vibrations died out 

 so that the motion of the pencil of the indicator became imperceptible, 

 after about 30 complete oscillations. 



Magnitude of Rise in Pressure following Sudden Closure of a Valve. 



If p r be the rise in pressure in Ibs. per square foot ; if K be the 

 modulus of cubical compressibility of the water ; and if v be the velocity 

 of flow at the instant of stoppage (supposed instantaneous), we have, 

 assuming the pipe line rigid, on equating the loss of kinetic energy 

 per Ib. to the increase in resilience : 



_ 

 2 g 



2 K w' 



!KW 



. (1) 



