ENGINEERING STRUCTURES 139 



into the open end of the vertical pipe ' E? this being either full 

 or partially full of water, thus simulating the conditions under 

 which a falling sea impinges on the pavement joints of a break- 

 water. The mean results of this work are given at a later 

 stage of the paper. 



Before studying the effect of jet impact on the coil, a series 

 of experiments was carried out to determine the pressures to 

 be obtained by definite water-hammer. For this purpose the 

 open end of pipe ' C ' was coupled up to a large tank, the level 

 of whose free surface was 4'5 feet above the outlet valve V. 

 Water was allowed to discharge through the coil under this 

 head ; the discharge was collected for a given time and 

 weighed and the velocity of flow computed, and the rise in 

 pressure behind the valve following a sudden closure of the 

 valve was measured. If ' v ' is the mean velocity of flow in 

 feet per second, the rise in pressure following an instantaneous 



stoppage of flow in a rigid pipe line is given by p=v\/ Ibs. 



y 

 per square foot, 1 where ' K ' is the bulk modulus of the water 



and ' w ' is its weight per cubic foot. The mean temperature 

 of the water was 45 F., at which temperature ' K '=43x 10 6 

 Ibs. per square foot, and this value makes p=9130 v Ibs. per 

 square foot =63 '4 v Ibs. per square inch. Actually the 

 stretching of the pipe line and its distortion under pressure 

 absorb an appreciable amount of energy and especially so 

 when, as in the present case, the pipe line is not anchored in 

 any way. A large number of experiments were carried out 

 with varying velocities of flow, and, as shown in Fig. 3, on 

 plotting, these are found to lie for some distance on a straight 

 line, and to give the result p=48 v Ibs. per square inch. 



' I K'W 

 Writing p=y- , where K r is the effective modulus as 



\j 



modified for pipe distortion this makes #'=24-6 x 10 6 Ibs. per 



1 Water Hammer in Hydraulic Pipe Lines, Gibson, p. 39. 



