Pressure regulation

[Daniel Stuelke <dstuelke@magick.net>]

SFreihof wrote:
> 
> In your mail you asked:
> > Also to the people building dry subs, how do you regulate the fresh air
> supply >and internal pressure? I've spent many sleepless nights thinking about
> it (it's >better than counting sheep) and have come up with a way to do it but
> I probably >just re-invented the wheel.
> 
> My understanding is that you merely replace O-2  consumed, since CO-2 produced
> is absorbed by the scrubber (lithium hydroxide, e.g.).  There is no net
> increase in pressure, and I assume you need only to keep the partial pressure
> (i.e. percentage) of oxygen within certain limits.  Also, it is wise to
> monitor the percentage of CO-2.
> 
> I'm not sure you can do this simply with a sensitive demand type regulator,
> because I would expect the hull flex at depth to increase the total pressure
> in the cabin above 1 atm.  I would think you must monitor % 0xygen.
> 
> I am sure there are ways of doing this automatically and maybe some components
> of scuba type rebreather system could be used.  These systems are now
> commercially available, but probably expensive.
> 
> I'm curious what method you devised?  Please share your design ideas, unless
> you intend to patent, of course.
> 
> Who out there can offer some guidance?
> 
> Stan Freihofer


 I am designing an all acrlylic sub. I have a small plastic fabrication
shop that I build aquariums in but I'm not set up to vacu-form veiw port
shapes yet I'll let you all know when I am. 

As for air supply- since my sub will be designed for relatively shallow
depths less than 30m I thought I would use a low voltage air compresser
and a metering valve to expell air at a constant rate and a SCUBA type
compressed air supply fed through a diaphragm valve to maintain a stable
air pressure.

 Since most diaphragm valves vent the "back side" to the atmosphere, the
vent will have to be fed to an airtight chamber large enough to allow
normal movement of the diaphragm. There could be some sort of volume
adjustment on this chamber to "dial in" barometric pressure.

 My sub will be very small and I have access to a SCUBA compresser to
refill my air tanks so it will be easier for me to use compressed air
than an oxygen supply and CO2 scrubber. With dropable ballast and maybe
a spare-air for emergency escape I think I can safely design a fresh air
system based on a two or three hour limit instead of a seventy two hour
supply.

 If anyone knows of a reason this type of system won't work or a way to
make it better I welome feed-back, It will be a few years before I start
construction so I may change my mind on a lot of things by then.

 Daniel.