Study and interpretation of the cavitation in a low pressure loop system equipped with water hammer control device

A water hammer protection device in lifting systems, especially in low pressure ones, has been experimentally studied by Giustolisi et al.(1,2,3). Water hammer, in the experimental tests of the analyzed device, is caused by a fast interception of the water flow by means of a spherical valve located just downstream of the hydraulic system pump. Such a device comprises a generic check valve and a concentrated head loss located at one end of a bypass; the latter must be installed between the upstream reservoir and the delivery pipe of the hydraulic system, downstream of the section in which the water flow cut-off has been generated, with the valve close to the reservoir. The valve allows water to flow from the reservoir to the delivery pipe through the bypass. The positive experimental results regarding the efficiency of this device bypass - check valve - concentrated head loss in protecting low pressure lifting systems from water hammer, have been the starting point for studies which have been directed towards the creation of a numerical model of the hydraulic system. The tests presented in Giustolisi ct al.(1,3) show that a numerical model, simulating the water hammer in a system equipped with the protection device under investigation, should be based upon models simulating cavitation. A numerical model that takes into account the occurrence of cavitation was developed in Giustolisi et al.(4,5). The further step of the study is to verify the simulation of cavitation in the numerical model, by repeating the experimental tests changing the material of the bypass. The bypass, an iron pipe in the previous experimental tests, has been substituted with a plexiglas pipe to film the cavitation during water hammer and to compare the cavitation model with the physical phenomenon.