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

Wed Dec 11 18:53:27 EST 2013

No. Anything is possible, I suppose, but I've never allowed the internal pressure to vary more than 1/2 to 1 inch of vacuum from absolute. If your cabin pressure is climbing in spite of that, then you need to look for a leak and fix it (thus the tool kit, which always carried appropriate wrenches and a bottle of Snoop). Plus we had the double acting vent line on the panel to vent or fill once back on the surface. I harp on and off about the tendency of some in our group to look for shiny cheap valves with suitable ratings. In my view it's the old yacht formula: Fast, cheap, comfortable--pick two. You can't have all three. In our case: Durable, dependable, expensive--pick three, every time. It's part of the price of doing business.

Vance

-----Original Message-----
From: Alan James <alanlindsayjames at yahoo.com>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Wed, Dec 11, 2013 6:19 pm
Subject: Re: [PSUBS-MAILIST] G.L. summary Pressure Hull

Vance,
have you had any experience of hatches flying open due to
over-pressure, (is it an issue with an over-pressure valve set low)
or know of fail safe mechanisms to ensure pressure
equalization before opening the hatch.
Thanks,
Alan

   From: "vbra676539 at aol.com" <vbra676539 at aol.com>
 To: personal_submersibles at psubs.org 
 Sent: Thursday, December 12, 2013 12:11 PM
 Subject: Re: [PSUBS-MAILIST] G.L. summary Pressure Hull

They use a small shop vac on the DWs. Cost thirty bucks. All you need to do is pull something measurable on your barometer, maybe 1/2" of vacuum, then close the valve and watch. If it holds, you go.
Vance

-----Original Message-----
From: Jim Todd <jimtoddpsub at aol.com>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Wed, Dec 11, 2013 5:30 pm
Subject: Re: [PSUBS-MAILIST] G.L. summary Pressure Hull

Alan,

You're right, and I think ABS also has the same cutoff requirement.  When I Iooked back at my design notes I saw that I did have a manual cutoff with the AOP.  I'd prefer to go with a light on the indicator panel instead of position near the latch. 

I'm familiar with the DW vacuum setup. Haven't done the calcs to see how long I'd have to let the little compressor run. Have to wear ear protectors I suppose. 

Jim 

Sent from my iPhone

On Dec 11, 2013, at 3:56 PM, Alan James <alanlindsayjames at yahoo.com> wrote:

Jim,
the Deep Workers have an external attachment for pulling a 
vacuum pre dive to set the seals. However they are boat launched
& it would be more of an issue if there was a slight leak in the hatch seal.
>>>  However I think I would like to have a way to cap off the AOP if it began to leak. 
G.L. Section 9 B, 1.2 .....Pipes which are led through the pressure hull wall
are to be fitted with two shut off devices, one of which is to be located
immediately at the hull wall.
    I am interpreting this as meaning that the over-pressure valve requires an 
additional valve, which makes it difficult to use the over-pressure valve to
fully equalize the hull.
Alan

   From: "jimtoddpsub at aol.com" <jimtoddpsub at aol.com>
 To: personal_submersibles at psubs.org 
 Sent: Thursday, December 12, 2013 10:02 AM
 Subject: Re: [PSUBS-MAILIST] G.L. summary Pressure Hull

Hi Alec,

It sounds like GL is setting up standards to idiot-proof operations.  The manual OP valve blocking the hatch latch is just for complying with their requirement.  I hadn't previously thought of a manual OP valve to go with the AOP.  However I think I would like to have a way to cap off the AOP if it began to leak.  

The interlock is for situations such as someone closing the hatch but forgetting to latch it or diving solo with the pilot's hatch closed and a rear hatch open.  Meticulously following the checklist prevents such disasters, but people sometimes screw up.  If not an interlock I would at least want indicator lights rather than depend on a rear passenger's assurances that all is latched.

I don't know if I would pull a slight vacuum before every dive or not.  Only experience will answer that.  I have a couple of very small 12V compressors around to try on a shop dive.  I may decide I like one and can find a place to mount it.  On the other hand it might be a slagiatt (Seemed Like A Good Idea At The Time) that gets discarded.  You've saved me from a couple of my ideas in the past.

Best regards,
Jim

-----Original Message-----
From: Smyth, Alec <Alec.Smyth at covisint.com>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Wed, Dec 11, 2013 2:21 pm
Subject: Re: [PSUBS-MAILIST] G.L. summary Pressure Hull

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>
To: personal_submersibles <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

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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