8.8 Water hammer

Water hammer occurs when the installation pipelines carry incompressible fluids such as water, ethylene glycol, etc., and the fluid flow suddenly changes its velocity. A common cause of water hammer is the rapid closing of a solenoid valve in the liquid line. Abruptly stopping the fluid flow produces a substantial pressure rise. High-intensity pressure waves will travel back and forth in the pipes between the point of closure and a point of relief, such as a larger diameter header, at extremely high speed. As it moves, the shock wave alternately expands and contracts the pipes.

Water hammer is the cause of many problems such as ruptured pipes and damage to valves, Bbrazed plate heat exchangers and other equipment. In a brazed plate heat exchanger, the water hammer will cause a bulge in the front or back plate, resulting in internal/external leakage (see Figure 8.44). To avoid or eliminate these problems, the designer can install an air chamber or a water hammer arrester. Another way to control water hammer is to use valves with controlled closing times or controlled closing characteristics. The graphs in Figure 8.45 illustrate the difference between using standard quick-closing water valves and slow-closing timecontrolled water valves.

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