In the recent discussion of hull penetrations, hull valves have been mentioned a number of times. While doing some peripheral reading for my naval architecture classes today, I cam e across an article that brought up some points that we should consider when choosing hull valves for a PSUBs. While the article is written for surface vessels, here are the points that are important to us:
1. Be careful when choosing a valve. Valves intended for industrial/household use are most often manufactured from brass. When used in marine applications the zinc will leach out of these valves (turning them a red color) resulting in the valve becoming structurally weak and the sealing surface potentially degraded. Many parts of these valves are carbon steel which will not hold up for very long in the marine environment. A bronze or stainless steel valve with a stainless steel ball and handle should be carefully chosen instead.
2. The American Boat and Yacht Council (ABYC) has established standards for marine seacocks. One of the most critical is that the seacock withstand a 500-pound load applied to it for a period of 30-seconds. ABYC also requires a handle that swings through a 90-degree arc and that the handle indicates whether the seacock is open or closed. In the tight confines of a typical PSUB, this is probably a good idea especially for valves in the vicinity of the conning tower as the valves may inadvertently be used as a step when entering or exiting a sub.
3. If you use marine seacocks, keep in mind that the connection on the hull side is NPS straight thread while the other end has an NPT tapered thread. If screwed on to a typical NPT nipple welded to the hull, there will not be much of a thread engagement if you can get it on.
Reference: http://www.thevirtualboatyard.com/2009/02/seacock-troubles.html#more
R/Jay
Resepectfully,
Jay K. Jeffries
Andros Is., Bahamas
Save the whales, collect the whole set.