[PSUBS-MAILIST] Life Support Alarms

[Jon Wallace via Personal_Submersibles]

 Sean,
Normal weather extremes were pretty much what I was thinking of as well.  However it turns out our pressure extremes are not very far from our daily average.  After some research of Buoy data here in the northeast it looks like over the last three years we've gone from lows of 988mbar to highs of 1041mbar, or about .4 psi on either side of "average".  That fits within my 1psi range although I could go with 2psi as Cliff suggested, as well.
If we think about SCUBA we know we are going to feel it in our ears somewhere around 3-4psi (180mbar?), so an alarm at 1-2 psi letting you know something is coming seems reasonable to me.
Thoughts?Jon

    On Sunday, December 13, 2020, 01:26:25 PM EST, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  
 
 On the subject of internal pressure, there are two different relevant design guidelines. One is to ensure that the vessel is capable of withstanding a positive internal pressure of one atm above ambient (with mandatory pressure relief above that), and the other is the optimum service pressure, which may or may not be a controlled parameter. If it is not controlled, then it will just be a consequence of temperature and moisture balance, and as long as the means are available to equalize with surface pressure prior to opening the access hatch, that variance should be inconsequential. You may want to introduce a slight vacuum with respect to the actual atmospheric pressure in order to test seal integrity prior to submergence, so any recommendation for operating cabin pressure would need to accommodate that. On the other side of the coin, the potential for gas leaks from pressurized sources could inadvertently raise the pressure of the passenger compartment, and you might wish to introduce active control over that with e.g. an on board compressor to draw it down, in conjunction with a valved flow restricted air source to raise it if necessary. In that case, I would be inclined to control it either to the measured atmospheric pressure at the time of lock-in, or to one standard atmosphere at 101.325 kPa. Not sure where I would set alarm limits. Probably I would look at typical atmospheric pressure variances at sea level and set limits outside of that?

Sean


-------- Original Message --------
On Dec. 13, 2020, 10:42, Jon Wallace via Personal_Submersibles < personal_submersibles at psubs.org> wrote:


I'm looking to start a discussion to create a PSUBS standard for max/min cabin operating conditions.  I'm not convinced temp or humidity matter all that much overall and require an agreement.  I would start with the following:
O2:    19.0 to 23 percentCO2:  0 to 5000 ppmPressure:  +/- 1psi
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