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Re: [PSUBS-MAILIST] hull test



Hi Byron.
 
Yes, I was using 14.7 psi as an average. I was wondering whether David was correct when he said if a hull in someones backyard was
 
vacuumed til it's interior was completely vacuumed, that it would have a psi of 14.7  It would seem to me once vacuumed to that condition,
 
to have a psi against the exterior hull pushing inward of  twice that and then be 29.4 psi  I think the hull can only be vacummed out to where it
 
has two atmospheres pressing against it, the atmosphere always existing around us, and the one it had sucked out of it which would
 
increase the pressure to two atmospheres.  Isn't that correct?
 
I got a bit confused with the hull within a hull thing Byron, did we come to the same conclusion? Lol.
 
Bill.
 
 
----- Original Message -----
Sent: Tuesday, October 25, 2005 5:37 AM
Subject: Re: [PSUBS-MAILIST] hull test

 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 -----
From: Akins
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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