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

Mon Sep 2 12:42:51 EDT 2013

Hi James,
Could you tighten down the hatch from the outside with  hold-down straps 
such as you use for securing a load on a trailer?  Or you  could place some 
weights on a platform on top of the hatch.
Jim

In a message dated 9/2/2013 11:30:30 A.M. Central Daylight Time,  
jamesf at guernseysubmarine.com writes:

Hi Guys,

Sounds like the overnight vacuum test is a really good idea.   
Unfortunately i only have the standard hatch so i cant close it from  outside .  I'll 
have to see if i can suck it down like Hank  suggests.  Got a few days to 
tinker.
Regards
James

On 2 September 2013 17:12, hank pronk <_hanker_20032000 at yahoo.ca_ 
(mailto:hanker_20032000 at yahoo.ca) > wrote:

Hi Jim,
I  am no expert on the subject, but I do a test with as much vacuum as  
possible.  When you dive the hatch is secured tight so there is always  
pressure on the seal.  Before I converted my k350 hatch to open from  both sides, I 
did the vacuum test without securing the hatch.  I does  not take much 
vacuum to suck the hatch down tight.  Honestly I am not  sure about a low vacuum 
test, you could be  right.   I just assumed it should be more than  less.   
Before I tested my last sub in the lake, I did a vacuum  test and I did 
loose vacuum overnight.  It was very minor, so I went  anyways.  Sure enough I 
had a leak, I took on a couple of litres of  water at 200 feet for an hr.  I 
think my connection point from the  acrylic cylinder to the hatch land was 
the problem.  There is no seal,  it is cast in place.   
Hank

From: "_JimToddPsub at aol.com_ (mailto:JimToddPsub at aol.com) " 
<_JimToddPsub at aol.com_ (mailto:JimToddPsub at aol.com) >
To: _personal_submersibles at psubs.org_ 
(mailto:personal_submersibles at psubs.org)  
Sent: Monday, September 2, 2013 8:57:18  AM
Subject: Re:  [PSUBS-MAILIST] Leak, pressure and life support test

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_ (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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