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

[Smyth, Alec]

Gents, I think we're seriously over-complicating this one. The automatic overpressure valves typically have a spring loaded stem. Want a manual valve? All you do is put your finger on the stem and press a little. You would do that if you wanted to open the valve at less than its cracking pressure, or just for a little ventilation when there is no pressure differential.

I'm not following the interlock part, because if the valve is automatic then you are always equalized and can't open the hatch in any other condition.

As for installing a compressor just for the purposes of pulling a pre-dive vacuum, in my opinion it has a way too high moving-parts-to-benefit ratio. You can pull a vacuum at the start of the day, on land or (I wish) on the deck of your support ship. But afloat before every single dive? I'm not aware of anyone doing that.

Best,

Alec

From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of jimtoddpsub at aol.com
Sent: Wednesday, December 11, 2013 10:20 AM
To: personal_submersibles at psubs.org
Subject: Re: [PSUBS-MAILIST] G.L. summary Pressure Hull

It seems that the need for sensing could be eliminated (as far as the present question goes) by positioning the handle for the pressure relief valve in such a manner that it would interfere with releasing the hatch latch unless the relief valve handle was in the open position.  In other words, you have to move the handle to out of the way before you can get to the hatch release.

Having a manual control handle doesn't preclude the relief valve from being automatic.  It just means the manual portion leading to the auto portion was open.  It seems like a good idea for the manual valve to be opened at some reasonable depth prior to surfacing so any overpressure is free to flow to the auto relief.  You don't want overpressure to blow the hatch open when you're still two feet below the surface.  If the relief system is entirely manual, you have to wait until surfaced to open the valve unless the overpressure is particularly high.

Jim


-----Original Message-----
From: Joe Perkel <josephperkel at yahoo.com<mailto:josephperkel at yahoo.com>>
To: personal_submersibles <personal_submersibles at psubs.org<mailto:personal_submersibles at psubs.org>>
Sent: Wed, Dec 11, 2013 8:54 am
Subject: Re: [PSUBS-MAILIST] G.L. summary Pressure Hull
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

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________________________________
From: hank pronk <hanker_20032000 at yahoo.ca<mailto:hanker_20032000 at yahoo.ca>>;
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org<mailto: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<mailto: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<mailto: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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