Seacocks, mixed blessing

It is part of normal maintenance, dealing with the various seacocks on the hull of our boat. Almost all of them, when above the inch in diameter, tend to get stuck due to deposits of limestone or vegetation and fauna at the inlet side. Among all, the most sensitive to this phenomenon are ball valves, now widely used in this type of location. These valves are also the less maintenable because the ball usually runs between two teflon seals or other synthetic material, once scratched, the tightness of the valve is gone forever even if you are able to free the ball again. The electrochemical corrosion that is stimulated by the difference in electrical potential with the through-hull bushing often contributes to further damage these components that are so vital for the safety of the boat. A type of valve used extensively in the past and whose invention dates back to the Romans, is the plug valve well known in the Anglo-Saxon and northern European countries. The plug valves can be easily serviced very well by means of simple crafts and grinding compound, an example of how to do this with photos at this link.
Many, like me, moreover, have repeatedly replaced the traditional 1 “1 / 4 stainless steel ball valve of the sewage discharge of the toilet, so that each shipyard has a quantity of them in the bin ready to be wasted. In the picture below, one of many that I removed from my boat and followed the same fate.
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A good replacement might also be a valve built with Marelon like the following picture, but also the latter is prone to get stuck by fouling and though they are quite strong, a plastic valve looks always more fragile than its metal equivalent should it be hit by a heavy object.
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Another type often used for this application is the gate valve, subject to the loss of tightness by fouling. An example in the following pictures.
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Last but not least, is the globe type, well known and well used on many boats for its good characteristics and lifespan like the one available in the following drawing.

This type as well, like the others, has the fluid that comes in contact with the stem at least in the open position getting the risk of an external leak and exposing the stem to corrosion.

After a careful search and some contacts with suppliers, I’ve found an innovative approach to a globe valve type that has been recently adopted by some of the most famous boatbuilders which is defined as anti-blockage. This valve has the globe coated by a rubber layer that continues in a sort of bellow that exceeds the flange of the cover, avoiding the fluid to come in contact with the stem and grants the tightness although the seat is moderately fouled. Also the maintenance of the valve is very easy and the cover can be replaced together with the globe and mechanism alltogether without the need to remove the valve from its place. Never forget that these valves are always the very last barrier against the ingress of water in the hull wich is our last resource of floatation. In the following pictures some images of such valve taken when installing it on my boat, also with cover removed to make the installation easer.
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