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Hi David. I think a piston pump would work fine for that.
Some sort of "ejection" tube powered by what ever system we choose seems
like a valuable system to have on a sub. You could use a compressor and
high pressure air tank, but the air would have to come from some where inside
anyway, so it seems like just using a scuba tank to "blow" the VBT is the
simplest. The important thing is, it needs to be valved off so the water volume
remains constant at different depths.
Vance's idea of using a soft "ambient" tank with a regulator to match
outside pressure sounds good too, but starts to veer away from the "KISS"
principle.
I have all the "stuff" needed for operation of my sub inside where I can
get at it. Batteries, VBT's, plumbing, sensors, and all, so if need be, I can
switch from "main system" to "back-up system" to "emergency back-up
system" without having to exit the sub. Plus, the fewer things outside, the
less I need to worry about moisture and pressure mitigation.
I won't have any computer controlled devices, and a minimum of electrical
equipment, so that "system failure" is minimized and replacement of a part or
device can be accomplished while remaining submerged.
I won't have any "rotating shafts" or other mechanical things puncturing
the pressure hull, and EVERY hole in the hull will have a ball valve on it, just
in case. ( except the hatch, of course.)
That whole "fly by wire" thing just scares me, as evidenced by the recent
crash of that Air France jet that was lost in the Atlantic.
I want my sub to be as simple and repairable as I can possibly make it.
Spare valves, switches, parts and pieces will be stored inside, so as a last
resort, I can affect emergency repairs while stuck on the bottom.
Frank D.
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