[PSUBS-MAILIST] instruments, pressure display?

Joe Perkel josephperkel at yahoo.com
Sun Dec 22 17:22:02 EST 2013 

Hank,

Are you testing beyond your pre-determined safety factor? Off the top of my head 3K psi would be north of 200 atm, somewhere around 6K depth.

Not having done any of this myself, I'm wondering if its more useful bringing any given component to a predetermined safety factor of whatever (1.5 to 3) etc., then hold it there for awhile. Destruction confirms known mechanical properties, we have to figure everything has a breaking point, so I wonder if testing to a point somewhere south of destruction is of more use? What do you think?

Joe



On Sunday, December 22, 2013 5:04 PM, hank pronk <hanker_20032000 at yahoo.ca> wrote:
  
Joe,
The failure was unremarkable, it was a pin hole size leak through the potting material.  I am not sure if the leak travelled along the bare wire first.  There is no way to tell, I did drill it out and the material was well consolidated and cured.  I have ordered new polyurethane because I suspect my old material has frozen one to many times.  I think I will stick to tried and true method though.  That is a single threaded rod in a threaded fitting with oversized washer.  I can pressurize one to 3,000 psi to see when and if it fails.  That is the limit of my compressor.
Hank 



On Sunday, December 22, 2013 2:48:55 PM, Joe Perkel <josephperkel at yahoo.com> wrote:
  
Hank,

What was the nature of the failure, leak, extrusion of potting material (epoxy) or a catastrophic mechanical failure? Knowing how things behave in failure is helpful in looking for potential warning signs ahead of time.

Your test program is pretty cool, a lot to learn here.

Joe







On Sunday, December 22, 2013 3:35 PM, hank pronk <hanker_20032000 at yahoo.ca> wrote:
  
Alan,
the fitting is tapered, it is pipe thread.  As a safety, I have a  washer of non conducting material under the nut to prevent the rod from pushing through the fitting.
Hank



On Sunday, December 22, 2013 12:16:38 PM, Alan <alanlindsayjames at yahoo.com> wrote:
  
I follow,
you are getting wicking down the wires, not a failure from
the epoxy extruding through the through hull fitting.
If your design did fail, It could be in a catastrophic manner.
I would want a bit of inward taper. Their is a perfect inward
taper angle, but not sure what it is. Aside from stopping the
potting mix extruding, the taper would compress the potting
compound around the wires under pressure
Alan

Sent from my iPad

On 23/12/2013, at 7:49 AM, hank pronk <hanker_20032000 at yahoo.ca> wrote:


Hi Alan,
>There is only thread on the inside of the fitting for the epoxy to grab, but that seem good.  I think the failure is from the smooth copper wire.  If I use threaded rod it works perfect.
>Hank
>
>
>
>On Sunday, December 22, 2013 11:45:18 AM, Alan <alanlindsayjames at yahoo.com> wrote:
>  
>Hank,
>so their is no taper or key to hold the epoxy,
>just a standard tube threaded on the outside?
>Alan
>
>Sent from my iPad
>
>On 23/12/2013, at 5:25 AM, hank pronk <hanker_20032000 at yahoo.ca> wrote:
>
>
>I just did a potting experiment, I removed the main  electric penetrator from my little yellow sub and pressure tested it to 1,000psi.  I left it over night and it held 1,000psi with no leaks.  That penetrator is my standard simple threaded rod in poly urethane.  I tried the same technique with 11 bare wires except I started with 5min epoxy for the first .75in  just to seal it to hold the very slow curing poly urethane from leaking out.  Well it failed at 1,000psi, I am not sure if is the small wire versus the larger threaded rod.  More testing :-) 
>>Hank 
>>
>>
>>
>>On Saturday, December 21, 2013 10:45:39 PM, Joe Perkel <josephperkel at yahoo.com> wrote:
>>  
>>Jon,
>>
>>As a diver I would say depth. The reason being that in a blow and go scenario you need to know that last depth and time to blow down to know your bottom time for what would be hopefully, a controlled ascent. Think USN dive tables.
>>
>>This is a big reason why I think I personally would limit my own personal maximum operational depth to 250' with a practical use somewhat less. I might design for a 1,000', but I'm not
 going there. I really don't think I would like to go any deeper than say something like the Andrea Doria in a homebuilt non certified sub. Conversely, I'd do Titanic in Alvin, Mir, or Nautile in a heartbeat if I got the chance.
>>
>>Pay close attention to that next 25 story building you stand next to and picture yourself ascending from street level to the roof line. You may need to stop at the 24th floor for a while, if you can control that last ten
 feet that is.
>>
>>Joe
>>
>>
>>
>>Sent from Yahoo Mail for iPad  
>>
>>
>>
>>________________________________
>> From:  Jon Wallace <jonw at psubs.org>; 
>>To:  Personal Submersibles General Discussion <personal_submersibles at psubs.org>; 
>>Subject:  [PSUBS-MAILIST] instruments, pressure display? 
>>Sent:  Sun, Dec 22, 2013 3:34:24 AM 
>> 
>>
>>
>>I will be displaying depth in feet.  Is there any practical reason to 
>>also display pressure?  It's easy enough for me to do so but it seems 
>>superfluous.  Which do you prefer, depth indicator or pressure 
>>indicator, and why?
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