Gate Valve Trouble

By: Frank Lanier

QuestionMy 1980s Taiwanese-built trawler utilizes a gate valve for the engine raw-water cooling intake. Is it OK to use gate valves below the waterline?

AnswerGate valves are troublemakers and are not recommended, particularly below the waterline. Not only is the worm gear and associated guts of the thing prone to corrosion and failure, it’s also possible for trash to prevent the gate from closing properly without you knowing it. Seacocks should meet all UL 1121 and ABYC (American Boat and Yacht Council) standards and recommendations. These include operation by a lever type handle (usually operating through a 90-degree arc) that gives a clear indication of whether the seacock is open or shut, and a mounting that will withstand a 500-pound force applied at the inner end of the attached fitting. If you replace your gate valve, you should also replace the through-hull, to prevent the possibility of thread mismatch. Seacocks and their respective through-hull must also be of the same material.


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