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In a message dated 3/4/2010 7:45:11 A.M. Pacific Standard Time,
jonw@psubs.org writes:
you end Hi Jon. Now you got me thinking......not a good idea this early in the
morning.
If the valve is on the outside with only the handle penetrating the hull,
how do you get the air into the ballast tank ? Is there a separate thru-hull for
the HP air line to blow ballast ?
On the maintenance as it relates to "exposure to problems" it seems with
the valve on the outside there is more chance for a problem with the valve.
Although the pressure inside versus outside of the valve is less, the
corrosion potential is greater as the valve is exposed to water from the
outside. Then there's the remote possibility that the exterior valve could be
impacted by something. Also, if only the handle penetrates and there's a problem
with the valve closing or opening, you can't get at the valve while submerged to
fix it.
For instance......let's say you're down 100 feet and the valve gets banged
or just plain fails. If it's open and you can't close it, you can't fill that
ballast tank with air. Your only option to surface would be to drop your
emergency weight, and when you reach the surface you wouldn't be able to blow
the other ballast tank or the sub would likely tilt and be unstable.
On the other hand, with the valve(s) on the inside, you can pump the air
into the pipe leading to the ballast tank, so no separate HP thru-hull for
air is required, and if either valve malfunctions you can get a wrench on it
from inside the sub. Again, you're down 100 feet, and one of the valves screws
up. By closing either valve the vent pipe to the outside is blocked. Shoot
air into the pipe and the ballast tank fills with air.
I made my sub like that. A 1" nipple enters the sub from the ballast tank
and has a "T" on the nipple. The branch has a small valve and air line attached.
The main line has the 1" ball valve and goes up the wall inside the sub where it
connects to another ball valve and penetrating nipple to the outside. This is
all "hard piped" except for a short HP hose with compression fittings used as a
"union" so the parts can be threaded. If any component fails along this line, I
can isolate the pipe from the outside pressure, dis-assemble it, make the
repair, and I'm back in business. The HP air line has a valve at the "T" and
another at the HP Air manifold. Both valves are normally closed until I need to
blow ballast. If I need to, I can take it apart while submerged, and even
re-configure the set-up like if one of the thru-hull nipples gets
banged/crushed. Re-pipe the vent to the other vent nipple, change where the air
goes in, or any number of routes to get rid of the water in the ballast
tank.
It sounds a little more complicated but really isn't. Two thru-hulls per
ballast tank, both are 1", with a valve on every connection.The "spares" box
will have a variety of extra valves, short nipples, HP hoses and
other replacement parts, etc.
I know Jay said we won't be doing repairs while submerged, but hey, maybe
we'll need to.
The same thoughts are incorporated in my electrical system. Four separate
36 volt circuits for the motors, each with it's own battery bank, fuses,
switches, thru-hull, controllers, etc. If one system fails for some reason,
I can shut it down and re-wire what's still good to another circuit. ( The 12
volt lights/controls circuit is another separate circuit, with a back-up
battery. )
Switching from one battery bank to another will most likely mean
moving some battery leads because I don't have any switches connecting one bank
to another. They are TOTALLY separate. Again, a little more complicated, but the
ability to isolate a potential problem is the goal here.
Frank D.
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