Abstract
This work is concerned with water hammer phenomenon at various static pressures. An apparatus was specially designed and constructed to measure the magnitude and duration of pressure waves occurring when the flow of water in the pipeline is suddenly stopped. An important feature of the apparatus is the valve which is actuated by a D. C. motor through a link arrangement designed to give a complete closure in 14 millsec. Experimental measurements were carried out at four test stations situated along the first half of the pipeline measured from the gate valve. Five values of static pressure between 7 and 751bf/in[2] gauge for nine different values of water velocity up to a maximum of 2ft/sec, were used as test variables. Results of the total of 180 experiments carried out during the investigation are presented in the form of graphs and tables. Semi-empirical equations were derived to express velocity of pressure waves as a function of duration of the pressure variations. Velocities of the pressure waves for the 1st, 3rd and 4th pressure pulse were found to be constant at 4000 ft/sec +/- 10%. In the case of the 2nd pulse, the velocity of the pressure waves ranged from 4000 ft/sec. to 900 ft/sec. as the extent of vapour cavitation increased. It is assumed that both air and vapour cavitation occurs over the whole length of the pipe. The extent of vapour cavitation depends on the difference between the pressure during the 1st pressure pulse and the vapour pressure of water. The suggestion is made that the range of static pressure should be extended to 100 lbf/in[2] gauge or higher and that high speed photography could be used to follow the progress of air and vapour cavitation.