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Check Valve Failures |
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On November 1, 1999 an incident occurred involving a 4" 900# Walworth full-port swing check valve. The check valve failed to close and prevent a reversal of flow. During the subsequent investigation, an error was found in the design of this check valve. The disc and hanger assembly of this swing check valve will pass top-dead-center and not fall closed due to gravity when installed in the vertical position. This valve was advertised by the manufacturer, Walworth, as acceptable for vertical orientation. Walworth, other manufacturers, and content experts all agree that a swing check valve installed in the vertical position should be designed to fall closed by gravity to ensure proper operation and prevent reversal of flow. Walworth has worked closely with us throughout the investigation. They have recognized this design problem and have reviewed the design of all sizes of swing check valves in the 600#, 900#, and 1500# classes. The following valves sizes were found to have this design problem. Check Valve Model and Class Sizes with Design Error
The 150# and 300# class valves are currently designed with the disc and hanger assembly attached to the cover. The design error is not present in these valves. The previous design of the 150# and 300# valves were not cover hung. Walworth did not provide information to determine if the old design of the 150# and 300# valves have the same problem. Walworth has stated they are in the process of revising their design of the check valves in question. Any new check valves built by Walworth will be of the modified designs
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