Modelling a protection device in a low pressure lifting system

A water hammer protection device in lifting systems has been experimentally studied, especially low pressure ones [1][2][3][7] (see figures n°1 and n°2, pages n°5 and n°6 of the paper). Water hammer, in the experimental tests of the analyzed device, has been caused by the fast water flow interception with a spherical valve located just downstream from the pump of the hydraulic system. Such a device is composed of 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, just downstream from the section in which water flow cutoff 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. From the trials presented in [1][3], the authors have noted that a numerical model, simulating water hammer in a system equipped with the studying protection device, must use theoretical studies from the cavitation and models reproducing it. Previously [2], a simulating model, without considering the possibility that cavitation occurs, was realized. As the new experimental trials show [1][3], having been carried out starting from steady velocities much higher than older ones [2], the previous simulating model can he applied only when cavitation does not occur.