Re: [PSUBS-MAILIST] Source for a demand regulator?

[Ray Keefer <Ray.Keefer@Sun.COM>]

Hi,

When I first heard about the bellows supply system my mind drifted to my youth
with this thought.

Remember learning about weather (barometric variences) with a balloon stretched
over the end of a can or bottle with a straw and tooth pick on top.
One end of the straw is glued  to the center of the balloon with the toothpick
glued to the other end of the straw. As air pressure descreased the balloon
bowed up lifting the balloon end of the straw and dipping the toothpick end.
As air pressure increased the balloon bowed down into the container taking
taking the straw with it and lifting the tooth pick end. The toothpick end was 
used as a pointer placed next to a card that could be marked to track the 
pressure changes.

My thought for our application was to do away with the straw and put a
small metal disk in the center of the balloon with a small guage wire
soldered to it.  Just above the disk is another contact. As CO2 gets
absorbed and the air pressure decreases the balloon would bow up and
make the contact. The contact would open an electrical solenoid valve
to let O2 into the cabin untill the increased pressure pushes the
balloon back into its air tight chamber, breaking contact, and shutting
off the solenoid.

The big drawback with this idea is that it is partially electrical.

I also don't know if some kind of membrain system (like balloon) is strong
enough to force open a valve on its own or not. Or how durable it would
be. I am trying to think of alternatives here.

Regards,
Ray


> Date: Wed, 5 Jun 2002 14:41:46 -0500 (CDT)
> From: John Farrington <jrf@prismnet.com>
> To: personal_submersibles@psubs.org
> Subject: Re: [PSUBS-MAILIST] Source for a demand regulator?
> 
> I've been trying to track down the metal bellows myself, with the
> intent of building one of those units myself.
> 
> Not knowing exactly which bellows to use, I contacted a manufacturer,
> and gave him some ballpark specs on the bellows.  "Approximately 'this'
> big in diameter, about 'this' long, needs to move about 'this' far, based
> on variations in 'this' much barometic pressure.  Not real specific.
> 
> His question back to me was 'How many thousands will you be needing?"
> 
> I said about 0.001 'thousand' of them.  We both chuckled.
> 
> So, it's going to be a bit of a challenge finding the exact one, at
> a reasonable cost.
> 
> But, if I can somehow manage to find an off-the-shelf bellows that would
> work, then the rest of the unit shouldn't be too difficult to make.
> 
> As Phil has said in his paper, it is a simple design that has proven
> to be very reliable - nice attributes for your life-support system!
> 
> If I make any progress on any of this, I'll definitely post a
> parts list to the group.
> 
> -John