[PSUBS-MAILIST] Hatch Closure Mechanism

[Stephen Fordyce via Personal_Submersibles]

Hi Alan,
Some quick maths shows that for a hatch 0.5m diameter, just 2PSI pressure
difference is a force of over 1000kg. I doubt gas struts would be very
useful in that scenario!

Cheers,
Steve Fordyce

On 31 Dec 2017 9:48 am, "Alan via Personal_Submersibles" <
personal_submersibles at psubs.org> wrote:

Ian, Tim,
yes I was thinking about a cam type latch dog as you described.
The automatic pressure relief valve that Emile has would automatically
reduce any pressure in the hull to the equalisers spring closure pressure,
maybe 2psi; then if you forgot to manually press this valve to fully
equalise,
any internal overpressure would be released as the hatch dog incrementally
released the hatch.
I guess the only reason for this law is to prevent damage from the hatch
opening explosively. Perhaps gas struts would be suitable to stop this!
Tim, I have a design for opening from the outside. There could be a grip
on the seaward side of the overpressure valve to equalise from outside.
I am feeling like I have some solutions now.
Thanks, Alan.

Sent from my iPad

On 31/12/2017, at 11:23 AM, irox via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

Although it doesn't have be to the same vent/mechanism as the hatch over
pressure safety.

Also, there is a requirement for opening the hatch from outside, to add
more complications (if you're strictly following regulations).

-----Original Message-----
From: T Novak via Personal_Submersibles
Sent: Dec 30, 2017 1:16 PM
To: 'Personal Submersibles General Discussion'
Subject: Re: [PSUBS-MAILIST] Hatch Closure Mechanism

Just to add a complication to the project, you will need to have the vent
accessible by someone on the outside too,  in case the sub has surfaced but
the operator is incapacitated.

Tim



*From:* Personal_Submersibles [mailto:personal_submersibles-
bounces at psubs.org <personal_submersibles-bounces at psubs.org>] *On
Behalf Of *Alan
via Personal_Submersibles
*Sent:* Saturday, December 30, 2017 12:51 PM
*To:* Personal Submersibles General Discussion <personal_submersibles at psubs.
org>
*Subject:* Re: [PSUBS-MAILIST] Hatch Closure Mechanism



Thanks Hank,

will have to think on this one. I want to let a novice dive my sub, so

the system needs to be bullet proof.

If I have some sort of lock mechanism I would need to be able to bypass

it if I needed to escape at depth. The pressure at depth would be apposing

the manual operation of the overpressure valve. You could flood the sub
first

but normally the hatch is un-dogged prior to the hull equalizing.

Cheers Alan





Sent from my iPad


On 31/12/2017, at 1:49 AM, hank pronk via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

Alan,

You could have a lock that prevents the hatch mechanism from opening that
is activated by turning the hatch vent.  I always vent before I one the
hatch anyways.

Hank



On Friday, December 29, 2017, 11:09:03 PM MST, Alan via
Personal_Submersibles <personal_submersibles at psubs.org> wrote:





Just doing some evening reading of the GL rules & noticed this rule about
hatches....

"the closing mechanism is to be designed in such a way that opening of

the hatch is only possible after pressure equalisation"

I am wondering what options there are for achieving this.

Has anyone had experience of the hatch opening with explosive force due

to internal over-pressure not being equalised.

Alan



Sent from my iPad



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