All three of the sinks (two heads and galley) on our Tayana 47 discharge below waterline and are fitted with swing check valves, presumably to eliminate the "fountain effect" in heavy going.
These check valves are close coupled to the sea cock and predictably, are totally frozen in place mid swing by marine
growth/ calcium buildup. This particular seacock was frozen and I broke the handle off resulting in the whole assembly needing to be removed from the boat
. It was actually doing it's job because it let the sink drain well enough but blocked the line enough to stop a fountain.
Questions: Are check valves on marine
sinks typical and needed? A search brought up very little on the topic. I'm wondering because my usual sources (Defender, Hamilton, Jamestown) do not carry or list what I think is the needed, modern replacement. They have the Groco PNC-1000 (0.45psi opening pressure) but I think I need/want the CV-100 (0.19psi opening pressure). The bottom of the sink is probably 2.5/ 3 feet above the seacock if I had to guess.
What is the standard configuration to solve this problem? Shouldn't the check valve be above the waterline so it does not see marine fouling?
As a side note, to get the thru hull
out I took a grinder to the outside mushroom and ground it off. The heat softened the sealant
and a few blows of a hammer pushed the the whole assembly into the interior
. Way easier than than the alternative for a thru hull
I knew I was gong to replace adn located in a very tight spot. In doing this I found that the hose to check valve connection was made with a threaded nipple instead of a proper hose barb fitting. The nipple sheared off flush with the check valve with very minimal force and I found the metal to be highly degraded. It lasted nearly 30 years so I don't think it was brass but either way it was a boat
sinking waiting to happen. Pretty scary.