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Hello David, I think it's a matter of what sub system reserves you want to use up. Electricity or compressed air for surface breathing during transit. I think it would be easier to install more SCUBA tanks then batteries. You might also consider using or replacing 200 bar/3000 psi SCUBA tanks with with 300 bar/4500 psi steel tanks that are hot dip galvanized. I started considering installing these high pressure tanks, after speaking with a SCUBA diving store owner at length about different tanks. I want this type of tank so I can have about the same amount of compressed air as I would have in two 80 size aluminum SCUBA tanks, but have it in a smaller form factor steel tank that will fit under my small stern deck, next to the conning tower. "The pressure vessel is normally made of cold-extruded aluminium or forged steel. An especially common cylinder available at tropical dive resorts is an "aluminium-80" which is an aluminium cylinder of 0.39 cubic feet rated to hold (about) 80 ft³ of 14.7 psi gas at its rated pressure of 3000 psi (in metric units, its internal capacity is approximately 11.1 litres, to be pressurized to about 207 bar). Aluminium cylinders are also used where divers carry many cylinders, such as in technical diving, because the greater buoyancy of aluminium cylinders reduces the extra buoyancy the diver would need to achieve neutral buoyancy. In cold water diving, where a diver wearing a highly buoyant thermally insulating dive suit has a large excess of buoyancy, steel cylinders are often used because they are denser than aluminium cylinders. Kevlar wrapped composite cylinders are used in fire fighting breathing apparatus and oxygen first aid equipment, but are rarely used for diving, due to their high positive buoyancy." I've also looked into the much lighter Kevlar composite cylinders, and the Carbon Fiber composite/RATT cylinders that are many times used in compressed air vehicles, for there light weight and extra buoyancy since they are to be mounted in the upper part of my sub, and they can hold very high amount of pressure. One item I was not aware of until today regarding 300 bar steel SCUBA tank was this data below. "300 bar DIN : (7-thread, G5/8) - these are similar to 5-thread DIN fitting but are rated to 300 bar working pressures. The 300 bar pressures are common in European diving and in US cave diving, but their acceptance in U.S. sport diving has been hampered by the fact that United States Department of Transportation rules presently prohibit the transport of metal scuba cylinders on public roads with pressures above about 230 bar, even if the cylinders and air delivery systems have been rated for these pressures by the American agencies which oversee cylinder testing and equipment compatibility for SCUBA (OSHA and CGA). Note that reference to M25 threads refers to the tank neck thread not the valve size." http://en.wikipedia.org/wiki/Diving_cylinder But then again you can avoid even that, by simply having a K-250 type snorkel mouth piece for surface breathing if there is not a means to seal off the bottom and open the hatch in an ambient. Like this dry ambient ResortSub. http://www.ivccorp.com/resortsubda.html Regards, Szybowski From: alanjames@xtra.co.nz To: personal_submersibles@psubs.org Subject: Re: [PSUBS-MAILIST] Over Pressure Valve Options Date: Sun, 28 Jun 2009 17:42:20 +1200 Hi David,
Ear drums aren't a problem as divers equalize them down to 100ft + (50 psi +)
You could use a pump to fill up your ballast tanks with air at the surface, but
I can't see any other use unless you wanted to pop your hatch open. Ambients
have more problems sealing their hatches as they don't have the large water pressure
on them that 1atm do after 10ft. If you over pressurised your hull the hatch sealing would be more of a problem
also you'd have to design the hull and view ports to take the internal pressure.
Hope that helps
Alan
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