[PSUBS-MAILIST] Acceptable cabin pressure swing

Sun Feb 28 10:57:54 EST 2016

Brian,Where to put the relief valve, in my opinion it should stay on the store shelf lol.   I have a vent valve in the hatch, it is a 1\4 inch valve.  If you have a 1\2 psi relief valve and you want it to open at the surface, what is the point in having it?  You want a relief valve to prevent your hatch blowing off or ports popping off.  Well if your at the surface it is to late, the relief valve needs to open on the way to the surface.  That means you need to surface super slow and stop at just the right depth and wait for the valve to vent off pressure before you continue to the surface.  So if your going to put a relief valve in you best go big, like Emile and Alec have  or it will be like waiting for a giant inner tube to deflate that has one pound of air pressure in it.   Your sub does not need a relief valve, can't hurt but no need in my mind, because you have small bolted ports and a good hatch securing system.  It would be different if you had a big dome that was not strapped  on like Gamma has. We talked a while back about this and I remember Alec talking about rubber straps holding the hatch down.  Now that is how I think it should be done.  As long as there is catch so the hatch can only open an inch or two.  Hank 

    On Saturday, February 27, 2016 11:20 PM, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 I guess if the relief valve is more than a couple of feet below the water line, that would be a 1/2 psi per foot, which would render the valve superfluous. Brian

--- personal_submersibles at psubs.org wrote:

From: Hugh Fulton via Personal_Submersibles <personal_submersibles at psubs.org>
To: "'Personal Submersibles General Discussion'" <personal_submersibles at psubs.org>
Subject: Re: [PSUBS-MAILIST] Acceptable cabin pressure swing
Date: Sun, 28 Feb 2016 17:36:06 +1300

I know Emile has had it working but is it  possible for the O’ring to dislodge with flow.  I think the the O’ring should be more captive like in a dovetail groove in Parker book.  It is nice and simple but it should be tested at different pressures and flows.  Comments?Hugh From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of Alan James via Personal_Submersibles
Sent: Sunday, 28 February 2016 7:59 a.m.
To: Personal Submersibles General Discussion
Subject: Re: [PSUBS-MAILIST] Acceptable cabin pressure swing I sent this attachment & a couple of pictures but I haven't seen it yet,so here is  just the attachment only.This could be adapted in to some sort of snorkel for air on the surface.Alan From: Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
Sent: Sunday, February 28, 2016 7:41 AM
Subject: Re: [PSUBS-MAILIST] Acceptable cabin pressure swing The problem with that valve is that it's just got a 1/4" diameter, and you really want it to handle large volumes. Emile and I as mentioned built our own and they're really easy to make. Interestingly we made them independently but what we came up with is identical. I know Emile posted his design here a while back, so it must be somewhere in the archives. I never made a drawing of mine, just made the actual valve directly since it's so straightforward. It's machined from a SS round and consists of just two parts. The main body is a cylinder with a bunch of holes drilled through it, and one central hole for the stem. This cylinder is welded into the hull. The other part is the cap, a shorter length cut from the same solid round but with an O ring groove around the edge and no holes. The stem goes through the body and screws into the cap. You put a spring on the stem and a wing nut to adjust the cracking pressure. That's it. If interior pressure is stronger that the spring, the cap lifts and in so doing opens all the holes.  Best,
Alec On Sat, Feb 27, 2016 at 10:07 AM, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Brian, see McMaster Carr part number 4620K41.  This has a 1 psi cracking pressure, not 0.5 psi that I mentioned earlier. Cliff

On Thursday, February 25, 2016, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Cliff,          Where did you find that 1/2 psi relief valve? Brian Cox

--- personal_submersibles at psubs.org wrote:

From: Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Subject: Re: [PSUBS-MAILIST] Acceptable cabin pressure swing
Date: Thu, 25 Feb 2016 19:05:00 -0600Jon for my boat, I have a pressure relief valve with a 1/2 psi cracking pressure to vent pressure while on the surface.  I have a high cabin pressure  alarm that triggers at 20 psia (5.3 psig) and a cabin lower pressure alarm set at 12 psia (-2.7 psig).   In the PLC I also record and display the cabin pressure at the time the hatch is closed and log all alarm states every second.   I have never had either a high or low cabin pressure alarm while diving.  I have had elevated cabin pressure caused by accidently having the backup manual O2 value open and a leak in an air fitting on anther occasion. Cliff On Wed, Feb 24, 2016 at 1:12 PM, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

I think this is somewhat subjective but what is general consensus on maximum cabin pressure swing (higher/lower) relative to hatch closing at the start of a dive before setting off alarms?  My thought is that an alarm should sound well before any point of emergency.  I'm considering sounding a warning at 2psi +/- and an alarm at 4psi +/-  but I'm not sure if this is too strict.

Jon
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