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

[JimToddPsub at aol.com]

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.
 
Best regards,
Jim
 
 
In a message dated 9/2/2013 9:21:58 A.M. Central Daylight Time,  
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>
To: 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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