[PSUBS-MAILIST] Hatch Closure Mechanism

[via Personal_Submersibles]

And speaking of springs, we always terminated each of the MBT blow lines (externally) with a check valve. It keeps the lines clear and you don't get water backing up to your panel valves at depth. TIP: Use ball type. The piston type check valves do an incredibly good impersonation of sustained flatulence. It makes the passengers giggle helplessly.
Vance



-----Original Message-----
From: via Personal_Submersibles <personal_submersibles at psubs.org>
To: personal_submersibles <personal_submersibles at psubs.org>
Sent: Sun, Dec 31, 2017 9:19 am
Subject: Re: [PSUBS-MAILIST] Hatch Closure Mechanism


You are almost always dealing with a vacuum when returning to the surface, which in any case you can control over time via the life support system. We used a 1/4" ball valve of the HP air bank to equalize. On the Perry boats, an external vent line was routed from the penetrator up to the conning tower and wrapped in an inverted 'J' over the aft viewport. That way venting out cleared the line. There was no over pressurization valve as such. We depended on pilots, not springs. I've seen a lot of chatter about potential leakage into the cabin from the valves and connections on HP air systems at depth. That's what the barometer is for. I've cancelled exactly one dive for that, and snugged up a couple of fittings on the job, as it were. That's why you always carry tools and a bottle of Snoop. It is also why we don't use hardware store fittings. Best quality materials and proper installation pays off in the end.
Vance



-----Original Message-----
From: Alan via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Sun, Dec 31, 2017 12:49 am
Subject: Re: [PSUBS-MAILIST] Hatch Closure Mechanism




River,
GL also requires an over-pressure valve so I think this is in addition to that.
As Steve pointed out, if the closing spring on the over-pressure valve is 
2psi then that is 620 lb. pressure (Steve makes it 1000kg) that the hatch
will still be seeing.
Wonder if Vance has any experience on this?
Alan


Sent from my iPad

On 31/12/2017, at 5:52 PM, River Dolfi via Personal_Submersibles <personal_submersibles at psubs.org> wrote:




Ooops, ignore that previous rule. I was reading the Lloyds of London rules, not German Lloyds.

"2.1
The access and exit hatches shall be provided with a closing mechanism which makes it possible to create, even when the submersible is surfaced, a sufficient contact force on the hatch sealing. Sealing systems for hatch covers shall be approved by the Society.
In addition the closing mechanism shall be designed in a way that opening of the hatch is only possible after pressure equalization has happened, see [4]."



Of course, now that I think about it, this requirement is redundant. If an overpressure valve is installed, there would never be high pressure in the cabin to need to relieve. If there is an underpressure, you wouldn't be able to open the hatch anyway!





Thanks,


-River J. Dolfi

rdolfi7 at gmail.com






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