RAF 88 is adjusted to eliminate hazardous pressure surges typical of water hammer conditions. A water hammer is caused by an abrupt shutoff of a pump or rapid closure of a main valve, causing a fast propagation of lowpressure front, followed by an extremely high-pressure back-wave.
A Series of pressure waves, each one composed of alternating low and high pressure is created within a few seconds. RAF 88 is a piloted hydraulic valve activated by line pressure. The valve has two pilots, for high and low pressure. Under normal conditions, the RAF 88 is closed. lt opens when the line pressure drops below a preset pressure, in anticipation to the following surge, and remains open until the fluctuations subside.
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