From my previous post about the late war UZO you can see in my drawing the power cable exiting out the bottom of the UZO support column. In the picture below you can see this cable entering the Conning tower (Green Arrow). If you look at all the cable openings in the Conning tower they all have small valve on them (Red Arrows). Why have valve 
Is it to drain water out of the opening or to pressure the seals with high air pressure or to add oil Does anyone know or have any commons
Sorry it took so long to answer, but as usual, computer problems and it took until I could get to a different computer to view the picture that you were talking about.
The valve is a safety valve, to be able able to shut off the through-hull opening if it leaks.
EVERY boat, or at least every surface boat I've been on, has such a valve wherever there's an opening (through hull) to the outside water. Since it's stndard, and in fact mandated by regulations, for such a shut offvalve for surface boats, I can't imagine that a submarine, designed to dive down a hundred meters or more, wouldn't also have such a valve.
The reason why it's a ball valve, instead of a simpler and cheaper gate valve, is so that it can be shut off with one quick 1/4 turn of the wrist in an emergency.
Not sure how they work with a cable running through them, but that would be the reason.
If you watch any movies where a sub is being depth charged, you'll see whenever the boat springs a leak at any of the interior pipes or through hulls, the crew goes around and shuts off valves that the pipe leads from. The leak may not always be where the pipe leads through the hull, but there will always be a valve somehwere that shuts it off from the outside.
