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A few thoughts on externally operated valves.....
I remember seeing a red sub owned by Gary in Michigan that
had remotely operated valves on the stainless saddle tanks. Over all the
sub looked well made, but it always had some small problem so never saw it
dive.
My thought here is that adding complexity to a basic system like
filling/dumping ballast tanks is not needed and along with the
complexity....unreliability is also added.
If the vent valves are outside the sub, and something happens to stop it's
operation, you can't fill the tanks and float up.
Now, I would expect a vent valve to fail in the closed position with a
spring loaded mechanism of some type, but there's still the chance that
something can get into the valve and prevent it from fully closing even if the
pneumatic system is fully functional.
With a remote valve, you need thru-hulls to operate it, so why not just
control the water in/out from inside the sub? The thru-hulls need to be larger
for carrying water, but all you need for each ballast tank is "one in-one out"
with an air line attached to blow the tank.
With the valves, air supply, connections, plumbing, and stuff inside
the sub, the chance of it plugging up are minimized, and if needed, the systems
can be blown out by switching valves and sending the high pressure air up,
down, or around, to blow out any small debris that might have entered the tanks
and found it's way to the valves.
It just seems to me that the added complexity of a remote valve, along with
the inability to get at it while submerged, makes less sense.
The only plus I can see is that a vent valve outside the sub can be very
large which makes dumping the air quick. My sub will be using 1 inch valves to
dump the air, and the ballast tanks should be able to fill with water in about
two or three minutes. OK, that sounds like a long time, but if anything funky
starts happening with the valves or venting system, I can fix it from inside the
sub.
The other issue is maintenance. If the vent valve is outside, exposed to
the elements be it sea water or sunshine, it seems like it might require regular
inspections and maintenance more often than a simple set of ball valves inside
the sub. With just the two ball valves inside, ( with a "T" connection for
injecting HP air )
the maintenance and inspection should be fairly easy, and replacement of
any valve will be simple and inexpensive. Just pull out the valve and put in a
new one. Replacement can't be done while submerged, but a ball valve
is a pretty reliable device, and inexpensive enough to carry spares.
A remotely operated vent valve, with it's air control valves, and related
thru-hulls and plumbing seems like an overly complex way to accomplish a
simple task like dumping air or water from an ambient tank.
Frank D.
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