Many hydro plants have cast steel butterfly valves used to shut off the penstocks and allowrnworkers to inspect and maintain the turbines. The valve discs were typically cast and the castingrnholes were plugged with steel cover plates. Failure of the cover plates may cause uncontrolledrnrelease of water into the penstock or scroll case, endangering staff working on or in the turbinernand preventing use of the valves for single device isolation. This article presents examples of the problem, with both unsuccessful and successful repair procedures.
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