Re: [PSUBS-MAILIST] Altimeters as leak indicators

[JimToddPsub@aol.com]

Very good point, Alec.  If you didn't have an overpressure valve, at least the altimeter would let you know you were about to get your butt kicked when you got to the surface!

 

I had thought that once I closed the hatch, pulled -2.5 psi (+5,000 feet on the altimeter), and verified no leakage, I would then bleed the air back in s-l-o-w-l-y, close all valves in order to return to 1atm, and dive.  However I'm now wondering if it would be better to retain slight negative pressure (maybe one lb) for submerging.  Would that complicate any of the equipment such as the O2 system?

 

What are the thoughts of all you experienced guys?  What have I not considered?

 

Thanks,

Jim

 

In a message dated 3/27/2012 3:43:19 P.M. Central Daylight Time, Alec.Smyth@compuware.com writes:

Just an aside related to this thread… remember Kittredge’s one accident as described in his memoir? He had a slow air leak into the cabin during the dive, and upon surfacing blew out the K-250 hatch dome and found himself outside the sub having been blown out of the opening. That story was the original reason I installed two things in Snoopy, an altimeter and an overpressure valve. I would point out the two go together.

 

Alec

 

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From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jon Wallace
Sent: Tuesday, March 27, 2012 4:06 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Altimeters as leak indicators

 

Probably somewhere around 2-3psi I would think.  Not sure about the rest of you but I have to start clearing my ears at around 6-8 feet of water pressure.  If you need to clear your ears in a 1ATM during operations, that indicates a problem of some kind which should send you to the surface.  The two main issues I can think of that you want to avoid is an internal pressure/dive duration that ends up requiring decompression; a high enough pressure level that introduces O2 toxicity.  Both of those situations would be difficult to get to without the pilot knowing something was wrong since even without any gas monitoring you'd be clearing your ears plenty of times.  Unless you are drawing a vacuum as part of the pre-dive systems check (like DW-2000 does) there should be no clearing of ears unless there's a problem maintaining 1ATM within the cabin.

Jon


On 3/27/2012 1:35 PM, JimToddPsub@aol.com wrote:

 

I think I'll add an onboard checklist for possible causes if the alarm goes off.  This brings up the question:  What level of cabin pressure increase should activate the alarm? 

 

I'd like to hear some answers on that one.