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14.7 is not constant, even at sea level.
Barometric pressure changes from day to day, even hour to hour. Ask
any pilot, or better yet, watch the weather channel. The thickness of the
atmosphere changes with weather. 14.7 is an average,not an
absolute.
Seawater is denser than fresh water. Ask any diver
who has set up his weights for the Caribbean and then finds himself working in
Lake Michigan. He will sink unless he takes off some weight.
If you took an open pressure vessel down
to 33 ft. of sea water, and placed it inside, say, a larger vessel open to
ambient pressure ( such as inside an underwater habitat), the air pressure
inside and outside the vessel would be equalized at ambient, i.e. a nominal 14.7
from the surface air, plus the fixed pressure of the weight of
water, for 29.4 psi. Seal up your vessel and take it to the
surface. It now has a positive pressure of 29.4 psi
----- Original Message -----
Sent: Tuesday, October 25, 2005 4:32
AM
Subject: Re: [PSUBS-MAILIST] hull
test
Hi David.
I know what you are trying to explain to Daniel.
That there is only 14.7 psi existing so that is all that can be
sucked out of the hull and after that is gone
there is nothing left but a vacuum from which nothing is left to suck
out.
But when you said once you vacuumed out all the
air there would be a maximum pressure on the outside of the hull
of 14.7 isn't that incorrect and shouldn't it be
double that figure? As a diver I know that the atmosphere that surrounds
our
bodies all the time at sea level is 14.7 That means the pressure exerted on the
outside of the hull BEFORE the vacuum
was started would also be 14.7 So once that single 14.7 psi atmosphere was sucked out of
the hull, wouldn't that mean
the hull now has TWO atmospheres pressing against it? The original one that is always and
even now pressing against the
bodies of each and every one of us right now, and
also another 14.7 psi pressing against the hull because you removed
the
original 14.7 atmosphere from inside the hull?
For a total of 29.4 psi pressing against the
hull?
Bill.
----- Original Message -----
Sent: Monday, October 24, 2005 6:25
PM
Subject: RE: [PSUBS-MAILIST] hull
test
The weight of the atmosphere is 14.7 pounds per
square
inch at sea level.
If you were able to create a perfect
vacuum, and pump
out all of the air from the vessel, the maximum
amount
of pressure on the vessel woulb be a maximum of 1ATM
or 14.7
PSI.
There isn't enough weight in the atmosphere to get any
more
pressure.
-David
--- daniel@tordaca.com
wrote:
---------------------------------
i think i´m missing
something here, why can i test it
only to 1 atm? whycan´t i suck 300 psi
out of the
hull? i think you guys know something idon´t,
please
explain it to me.Thanks.
-------- Original Message
--------
Subject: Re:[PSUBS-MAILIST] hull test
From: "Emile van
Essen"<2stroke@hetnet.nl>
Date: Mon,
October 24, 2005 3:44 pm
To:<personal_submersibles@psubs.org>
Yes,
thats a pity; youcan only test it to a virtual
10
meter.
However....... It is avery good leak
test.
Emile
>
> The problemis you can only
vacumm 14.7psi out the
pressure vessel.
>
> Ian.
>
>
> On Mon, 24 Oct 2005 09:37:28-0700
> daniel@tordaca.com wrote:
>
>> helloevery one, i was thinking that to test the
presure
hull,the
>> pressure of the outside of the hull shuld be
X
timesthe pressure
>> inside the hull depending on the sub
design,for
example to test a
>> k-350 you should take it about
600 ftdown the water
to make about 300
>> psi press against the
subhull, now, those test are
not simple, i have
>> read all
thework that Dan H did to make this test
and
suddently
>>something flashed my mind, if i have to put 300
psi
of pressureoutside
>> of my sub hull, why don_t just vacumm
300 psiinside
the hull, i mean,
>> by doing this i will have
done avery similar thing,
there will be a 20
>> ATM
differencebetwen the inside and the outside of
the hull, but i
can
>> dothis test in the back yard of my house with a
small
vacum pumpand
>> not risking to lose my sub to the sea....
Please
thoseof you that have
>> done this test, and have read
about doingthem let
me know what you
>> think....Best Regards to
all.Daniel
>>
>>
>>
>>
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