Abstract
A generation mechanism has been developed describing the surge pressures produced in the return line during the decompression cycle of a hydraulic machine press and a mathematical model produced capable of predicting the pressures with good accuracy suitable for practical usage. Experiments were carried out on a small-sized model dynamically similar to a real machine in the 2000-ton (20-MN) class. Concerning fluid transient phenomena, the following three topics of industrial interest were mainly examined. (1) the pressure surge produced during the decompression process, (2) the cavitation duration following a column separation and (3) the pressure surge at the collapse of the first cavity. Particular attention has been paid to observating the mechanism of appearance of gas bubbles near the downstream valve, and of their growth and sequence collapse. The calculated values from the proposed "bubble model", in which the effects of gas (air) released from the liquid at the early stage of decompression and of surface tension due to a minute gas bubble were taken into consideration, agreed with the measured results with errors within some 10% under ordinary operating condition.
