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

Wed Dec 11 15:22:51 EST 2013

A message I posted about four hours ago just came through right after I posted a much longer version of the same one and re-sent it.

For the interlock to prevent diving without the hatch being latched, you could get a switch such as washing machines use to prevent the tub from spinning when the lid is open and install it at the hatch latch.  The other end could either block the vent controls from moving or go to inline switches/valves depending on how the MBT vents are actuated.
Jim

-----Original Message-----
From: Sean T. Stevenson <cast55 at telus.net>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Wed, Dec 11, 2013 1:54 pm
Subject: Re: [PSUBS-MAILIST] G.L. summary Pressure Hull

Is it possible that this rule is simply another way of stating that hatches need be designed to seal with pressure, such that they physically cannot be opened unless equalized (+/- a person's strength)?  Dogs in that case are just a means of providing a little bit of precompression on the O-ring in the absence of a pressure differential, and to hold the hatch against _slight_ reverse pressure, such at the 1 ATM specified by ABS.
ABS' version says that a means must be provided to equalize pressure before opening (needle valve?), that means must be provided to determine the pressure on either side, and that interlocks must be present to prevent e.g. submerging with open hatches.
I wonder if GL is really that prescriptive, or if we're misinterpreting?
Sean

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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