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

[Alan]

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 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 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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