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[PSUBS-MAILIST] Dry-Ambient pressure equalization
Hi all!
Dave asked me to explain the 3 method to equalize
the pressure inside a dry-ambient.
First of all, I do not consider myself an expert.
So if anybody don't aggree with me or see that I made a mistake, fell free to
clarifie please!
ok,
#1: Scuba regulator: the regulator is outside the
sub. You remove the mouthpiece and plug the regulator to a hole in the hull
where the mouthpiece was. Kind of like if you inside the hull could breath with
the regulator by sticking you mouth on that hole... The regulator will do the
job to equalize by adding air inside the sub as soon as it sens a pressure
difference between the inside air and the water pressure.
The good: fully automatic. Minimum air
compsumption. Reliable. Availeble.
The bad: always a small pressure difference in/out.
Reliable but still a mechanical device...
#2: Pilot driven pressure relief valve: About the
same as scuba regulator exept that this time you use an industrial valve. I'm
not very familiar with this method. I stopped looking at it when I say the price
for a valve like that (700$ us). The the principle is the same as the scuba
regulator.
The good: fully automatic. Minimum air
compsumption. Reliable. No pressure difference.
The bad: Price$$$. not easyly availeble. Reliable
but still a mechanical device...
#3: Natural equalization: This method is very
simple. Drill a hole at the bottom of the sub and plug a hole from that hole
under the sub. I recommend about 2 feet long. The hose is outside. Then, you put
a manual valve inside the sub on the hole. After the valve, you put a clear hose
all the way up inside the sub and make it loop all the way down the sub. You
then need a constant air supply. Et voila! when you closed the hatch, open the
valve and let air comming inside the sub. When you dive, watch the clear hose.
If water come up the hose, slow down the dive or augment the air intake. The 2
feet hose outside the sub will give you a 1 psi positive pressure inside the
sub.
The good: Very reliable. Cheap. Positive
pressure.
The bad: More difficult to operate. Untested (as
far as I know).
That's it!
Question, comments?
Pierre Poulin