WATER HAMMER 



241 



At the valve this wave is reflected with a velocity which is the difference 



between 2v and the velocity of efflux at this instant, and with a 



corresponding pressure. As the velocity of efflux will now be greater 



than v, the wave velocity will be less than v t and the rise in pressure less 



than 2 } above normal. This 



wave is reflected from the inlet 



to the valve, and here the cycle 



is repeated, the amplitude of 



the pressure wave diminishing 20ite.\ 



rapidly until steady flow 



ensues. 



Fig. 108 shows the diagram Fio. 108. 



obtained by the author from 

 the experimental pipe line under these conditions. 



Where the pipe slopes upwards towards its inlet, so that, beyond a 

 certain point in its length the absolute statical pressure is less than the 

 drop in pressure caused at the valve by sudden opening, then on the 

 passage of the first wave of negative pressure the wave motion becomes 



opened. 



Valve 

 Valve 



C/osecf. 

 Open- Steady flow. 



partially discontinuous after this point is reached, 1 and the wave travels 

 on to the inlet with a gradually diminishing amplitude. The amplitude 

 with which it reaches the inlet, and which will be probably 2 or 3 Ibs. 

 per square inch less than the absolute statical pressure at inlet, decides 

 the state of velocity of the reflected wave. This will evidently be less 



1 Actually before this, since water gives up its dissolved air rapidly when the pressure falls 

 to within 2 or 3 Ibs. of a complete vacuum. 

 H.A. 



