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RE: [PSUBS-MAILIST] Flooded Stability.
Jon, I would be surprised if the pressure was as high as 15 psi. Vance guessed at 2 or 3 psi. I would think that 5 psi would be acceptable and that the 15 psi mentioned is so that people could not get into a decompression scenario as was mentioned earlier. 15 psi is a fair internal pressure to seal viewports against and even more of a concern if you were to be at 15 psi and then equalized the sub too quickly causing ear problems. Some of those big domed windows were held on with straps which did not seem to have very big threads on their fastenings form memory. Maybe Vance can rack his memory cells again. Hugh
-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jon Wallace
Sent: Thursday, 25 March 2010 6:24 p.m.
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Flooded Stability.
Hugh,
I found it under 9/5.5 and 9/5.7 which is what I think you meant, and
not chapter 10. I believe the answer to your question is dependent upon
what you define as the maximum allowable working pressure (MAWP). In
the case of a submersible we might intuitively define MAWP as 1ATM, but
the wording of rule 9.5.7.1 does not require that. In the case of a
K-350 for example, there's nothing to stop a pilot from pressurizing it
to 3ATM and operating it as a semi-ambient vessel. Not realistic of
course, but given the language of 9.5.7.1 it would meet ABS standards if
you wanted to use a 45psi relief valve.
For practical purposes, I believe you want the relief valve set for
15psi which is the maximum normal operating pressure that most 1ATM subs
would strive to achieve. Rules 9.5.7.1 and 9.5.7.2 are poorly worded in
my opinion and appear to be drawn from language not originally
applicable to human-occupied pressure vessels. You could interpret
"normal operating condition" as written in 9.5.7.2 to mean "operating
condition" (15psi) or "physical condition" (the sub may be fabricated to
sustain a maximum pressure of 300psi). I suspect an inspector would
interpret it as operating condition, which really is the only thing that
makes sense.
Jon
Hugh Fulton wrote:
> Hi Jon, ABS 10-5.5 and 5.7 Pressure vessels and hx are not to be located within the pressure boundary ---------unless calcs show that inadvertent release of the contained fluid(s) will not increase the pressure inside the chamber by more than one atmosphere. 8/7.5.2 also.
>
> The cracking pressure on some relief valves you would be lucky to have it under 2 psi. But if you had 5 psi then on a hatch with a seal on it OD of 24" would have one ton pushing it open. I am trying to do the holding down with two catches but if the hatch is supposed to take one atmosphere then there is 3 tons to contend with. If you arrive back at the surface with 1 atmosphere and given that the 15 psi is in keeping with oxygen partial pressures limitation, then that could be a fair amount of air to pass out through the relief valve. Regards, Hugh
>
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