Pressures were measured during water hammer in a steam condensate system. The water hammer mechanism was verified to be vapor collapse in the piping as a pump started, using an ultrasonic measurement of pipe fluid levels. Before the pump started, an overhead pipe was partially full of water. When the pump started, the pipe became filled nearly instantaneously. The vapor collapse created audible water hammers and resultant shock waves in the piping. The shock waves were eliminated by controlling the pump start up using a variable frequency drive (VFD). A slow start prevents the sudden collapse of the vapor space and eliminates the water hammer.

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