[PSUBS-MAILIST] Leak, pressure and life support test

[JimToddPsub at aol.com]

Hi Alan,
 
I'm going to strive for no-leak just from securing the  hatch.  At the 
least I expect that means machining the landing before the  tower is welded in 
place and again after it's welded in place.   Dan and Alec experimented 
somewhat with the O-rings to achieve a  solution.
 
Jim
 
 
In a message dated 9/2/2013 11:47:02 A.M. Central Daylight Time,  
alanlindsayjames at yahoo.com writes:

Jim, Hank,
I was talking to a sub pilot who had had 10,000 hrs diving various  
submarines.
He said they all leak for the first few feet, even the $3 million dollar  
one he was working
on. Phil said they pull a vacuum on the Deep Workers before they dive to  
set the o-rings.
Maybe that avoids initial leaks.
Bet Vance could enlighten us here.
Alan

Sent from my iPad

On 2/09/2013, at 4:57 PM, _JimToddPsub at aol.com_ 
(mailto:JimToddPsub at aol.com)  wrote:



 
Hi Hank,
 
See if you agree with my line of thinking:  At a  hatch depth of 20 feet 
you'll have about 9 psi differential on your hatch  and your other 
penetrations as well.   At a hatch depth of 1 foot  you have about .445 psi 
differential.
 
For many things, the greater the pressure differential,  the greater the 
chance of a leak or seepage.  However on the hatch in  particular (and 
possibly on some other things), the greater the  pressure forcing the hatch against 
the landing, the more tightly it  will seal.  So the hatch might seal well 
at depth, but leak when barely  submerged
 
It seems it would be good to do both a high vacuum  and a low vacuum test.  
If the hatch seals well at high vacuum,  but leaks down at low vacuum, more 
work is needed on the latches or the  mating surfaces.
 S







Best regards,
Jim
 
 
In a message dated 9/2/2013 9:21:58 A.M. Central Daylight Time, 
_hanker_20032000 at yahoo.ca_ (mailto:hanker_20032000 at yahoo.ca)   writes:

 
Hi James,
I always do a vacuum test before my test dives.   I use a compressor as a 
vacuum pump and draw out as much air as  possible.  Then I have a valve on 
the hull and a vacuum gauge.   I let it sit for 24 hr.  If it holds the vacuum 
your set.   
Hank



 
 

From: James Frankland <_jamesf at guernseysubmarine.com_ 
(mailto:jamesf at guernseysubmarine.com) >
To: _personal_submersibles at psubs.org_ 
(mailto:personal_submersibles at psubs.org)   
Sent: Monday, September  2, 2013 3:45:27 AM
Subject: [PSUBS-MAILIST] Leak,  pressure and life support test



Hi All,
 
I did some tests at the weekend.  Very small pics attached as i  havent 
updated my site yet.
 
First i tested the battery pods and seals with  old inner tubes.  Managed 
to pump them to about 5psi.  Not much  but i think it was ok to indicate any 
leaks.  I couldnt see or hear  anything and pressure remained steady.
 
Then i did the very sophisticated "saucepan test" over the hatch  viewport. 
 I was just a bit suspicious of this one as it has no  gasket, the lense 
seats directly to the face.  No leak, but agreed,  not much test pressure 
although the saucepan was full despite the spillage  out the sides.
 
Next i did a life support test.  I filled and ran the scrubber  and then 
sat inside for an hour with the hatch sealed.  CO2 seemed to  level out at 
about 5500ppm and i topped up O2 when it got to  19%.      
 
i also dropped half a psi of internal pressure and that seemed to  hold, so 
i am hoping the boat is tight.
 
I was going to do a leak test in a local fresh water resovoir,  but as im a 
bit more confident its not going to leak now and its such a  logistical 
fuss, im going to go straight in the sea.  Next  week.
Kind Regards
James
 


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