[PSUBS-MAILIST] G.L. summary Pressure Hull

[Alan James]

Hi Doug,
Elaborating on your idea.
If you had digital pressure gauges you could have a system
comparing the voltage of the two, & when they were in a 
similar range they would activate or deactivate an electromagnet
that pulled back a latch that was impeding the movement of the hatch
release mechanism. (car door lock mechanism) You would
need a manual over-ride. Any electronics nerd could do this easily
& the car lock mechanisms I've seen for round $20-
With the over-pressure valve set at a couple of psi you know

that on the surface the most over pressure there could be is
what your over-pressure valve is set at. Under-pressure is
not such an issue as you won't be able to physically open the hatch 
if the under pressure is too much, & hence you have to equalize.
So I don't think it needs sophisticated monitoring. 
I'm not sure how much of an issue it would be if you opened your
hatch with a couple of psi over-pressure. Would the dome fly
open at 90 miles an hour, or would pressure be released incrementally
as the hatch dogs unlatched before fully releasing.
Obviously G.L. thinks this is an issue.
Alan


________________________________
 From: Douglas Suhr <spiritofcalypso at gmail.com>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
Sent: Thursday, December 12, 2013 8:06 AM
Subject: Re: [PSUBS-MAILIST] G.L. summary Pressure Hull
 


I have to admit this one really befuddles me. What if you were to have two (independent) pressure sensors/gauges, one for cabin pressure and one for ambient pressure, but the gauges were linked at the needles with a one-way gate. This way, the gauges would both be free to move independently, but the gate would only open (and unlock the hatch lock-out via a switch) when both needles were lined up in tandem indicating equal pressure, be it at the surface or underwater. I think actually designing and building such a device would prove very difficult.   

Is this what they are talking about, or am I confused? 

Because if so, I'm not sure I would ever want to implement such a device on my vessel. If a malfunction of this system were to occur during an emergency egress, how much more time would it take to bypass the hatch lock-out? 3 seconds is a long time when you are dying!  

With pressure gauges alone I will have a pretty good idea of where I stand in terms of equalization. 





On Wed, Dec 11, 2013 at 9:53 AM, Joe Perkel <josephperkel at yahoo.com> wrote:

Alan
>
>No definitive answer but we can postulate that both sensing and actuation are involved. 
>
>On sensing, differential pressure on either side of the hatch is translated to a impulse to actuation.
>
>On actuation, a method of locking out the operator from physically un-dogging the hatch, is the only way to meet the standard as per your O.P.
>
>Joe
>
>Sent from Yahoo Mail for iPad 
>
>
>
>________________________________
> From:  hank pronk <hanker_20032000 at yahoo.ca>; 
>To:  Personal Submersibles General Discussion <personal_submersibles at psubs.org>; 
>Subject:  Re: [PSUBS-MAILIST] G.L. summary Pressure Hull 
>Sent:  Wed, Dec 11, 2013 2:36:26 PM 
>
>
>
>Alan,
>Is this equalization from overpressure inside the hull? or external pressure.  
>Hank 
>
>
>
>On Wednesday, December 11, 2013 1:23:21 AM, Alan <alanlindsayjames at yahoo.com> wrote:
> 
>Can anyone enlighten me on what sought of mechanism
>is used that renders the opening of the hatch possible only after
>equalisation, as per G.L. Requirements?
>Thanks
>Alan
>
>Sent from my iPad
>
>On 11/12/2013, at 3:01 PM, Alan James <alanlindsayjames at yahoo.com> wrote:
>
>
>Hi,
>>I'm not covering much in this section because if I started on construction
>>regulations, I would just be duplicating what was printed.
>>G.L. wants you to have manufacturer certificates for every non structural screw.
>>Any company you contract to do your welding has to have their facilities, personal
>>& supervision approved by G.L..
>>Some points of interest are.... hatches need to be opened from both sides, they need
>>to be able to be secured open, they need to be designed in a way that opening of the
>>hatch is only possible after equalization. Two measures are required to guarantee that
>>the hatches are closed & secured before diving; one measure is to be visibly noticeable.
>>Mechanical measures for stopping a banging of the hatch is required.
>>Any external through hulls are to be protected against damage by appendages or covers.
>>If you are doing calculations on a computer you have to prove that the program is suitable.
>>Alan
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