Re: [PSUBS-MAILIST] re: 1atm subs

["Paul Suds" <paul_suds@hotmail.com>]

You wrote:
a
blowoff valve will not work if the pressure outside is greater
than inside
so do you use a air pump to pump it out (more calculations what
size pump)
Troy

Troy, when designing my sub (I have extremely limited personnel space), I 
had to take this into consideration. I thought about a small vacuum pump, 
but considering I'd only be down an hour, and the pressure from O2 and - CO2 
scrubber, would only build up to an additional 7 psi after 6 hrs (5 hr 
reserve). This is assuming staying below 15 ft for the entire hr (not 
likely, but possible). Upon ascending, a check valve (pressure relief valve) 
would open and start bleeding off air. I'm looking at a pilot operated SRV, 
which is actually safer, but more complex. Anyway, it depends on your 
approach. If you want to pump it out, you still have to have an opening and 
a check valve. The pump size can be extremely small similar to one of those 
emergency tire inflators for your car.
Suds

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