Cases occur in large water pumps, wherein, after installation, vibrations exceeding allowable limits are found to set in when starting up, and as a measure to meet such situations without resorting to reconstruction of the pump itself, a method of “preopening” is presented in this paper, which consists of opening up the delivery valves to a certain extent while the pump is gradually being worked up to full speed. The method of estimating the quantity of reverse flow, the torque required, and the time necessary for attainment of normal speed is explained. An example of application in actual practice is further given.

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