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Los Angeles County
Waterworks Division
California, USA

The altitude pilot valves are spring and diaphragm operated, three way pilots that control the water level in a reservoir by sensing the hydrostatic head. When the hydrostatic head equals the spring force, the pilot connects port “X” (connection to main valve inlet ) to port “K” (connection to main valve bonnet). The main valve closes. When the hydrostatic pressure decreases slightly, the port “X to K” connection is closed by the inner valve. When the hydrostatic pressure is reduced even further, the pilot connects port “K” (main valve bonnet) to “EX” (exhaust to atmosphere). The main valve opens.

The precise controlled transition from open to close operation requires that a minimum, non-adjustable pressure differential exist between the inlet pressure (port “X”) and the hydrostatic head (reservoir level) before port “K” is connected to port “EX”. This pressure differential varies with the spring range. The model 301-4 is used as the standard pilot on all 106 and 206 seriesaltitude control valves.