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

[VBra676539@aol.com]

In a message dated 3/17/00 9:51:21 PM, porpoise@midcoast.com.au writes:

<< So I've got into my pressure hull I close the hatch I turn on the air 
here's

my problem the longer I keep the hatch closed the higher the pressure

becomes in the sub.

I realise this is probably ellimentry but how have you all solved this, 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,

Turn on the air? Do you mean oxygen? If so, you have to get to the basics. 
You dribble in oxygen at a rate more or less exactly the same as required by 
the pilot. That's the people gas and you burn it up, thus no increase in 
pressure. Your carbon dioxide however, builds the pressure up internally, and 
the scrubber, by removing same, brings the pressure down. All things being 
equal, and ignoring temperature/density changes in the cabin atmosphere, you 
will have about the same internal pressure an hour later that you had when 
you closed the door and went diving. You will need a relief system for the 
sub; something as simple as a very lightly sprung check valve will do the 
trick. Overpressure will unseat windows and doors and is something you will 
not be too thrilled with. When your hatch lifts and bubbles it will sound 
like a percolator and feel like a winter rain storm in Lerwick. Cold and 
DAMP. I hate it when that happens. I've never seen a pump used to control 
atmosphere in a small sub, There is a first time for everything, so would be 
interested to hear about it.

Best Regards,
Vance