Dan,
As of yet, I don't have a scrubber or O2 supply in my sub. For now, I never stay down with two people in the sub over twenty minutes. That's my rule. I set a timer and return to the surface when it times out. So in actually, it's about thirty minutes from closing the hatch to opening it again. There is a pretty good cushion as I do it. Besides, my wife is more comfortable with me touching base on a schedule like that. (she muttered something about the life insurance not being paid up or something) I had considered an O2 tank when building my sub. It would be nice to extend my bottom time.
Even though you do not have O2 on board do you still have gauges to measure CO2 and O2 content in your sub to back up your 20 minute dive rule?
Kittredge used to carry a 02 tank inside his sub, and then after the space capsule disaster, he moved it outside and piped the O2 in through a hull penetration to a valve in the sub. I was debating when building my hull whether to put the through hull in or not. My thoughts were and still are; a tank inside the hull is not leaking or it would be empty. A tank outside of the hull would have to be turned on before putting the sub in the water. The valve inside the hull may be leaking a bit and I may not know.
I would have thought if you had the contence gauge inside with you, along with a separate O2 monitor you would be able to detect a leak and act accordingly.
Unless the tank or valve ruptures, I don't see the danger of it being inside the sub. I know it's not leaking O2 at the time I'm in the sub if it has sat in there for a month or so already. If I want to extend my bottom time with supplemental O2 and discover my tank is empty I have to surface and go back to my twenty minute schedule. I could carry two smaller medical tanks.
I believe the ABS regs state that gas cylinders should be mounted outside so that a leak will not increase the internal pressure to a toxic / dangerous level. By the same token the volume of gas stored in internal pipelines should be kept to a minimum (by the use of regulators or short runs of pipe) so that if released it will not increase the internal pressure beyond a certain level. This all seems to make sense but it does mean at least one more penitrator through your hull and another stop on the inside.
H
Any thoughts? Dan H.
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