[PSUBS-MAILIST] Hatch Closure Mechanism

[Alan via Personal_Submersibles]

Thanks for the maths Steve,
yes could wreck the struts with that sort of explosive pressure, or be
difficult to un-latch without equalising first. There could also be the situation
where the sub cools down with the hatch closed, pulling a vacuum.
Will go back to the drawing board!
Alan 


Sent from my iPad

> On 31/12/2017, at 12:41 PM, Stephen Fordyce via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> 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] 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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