[PSUBS-MAILIST] Acceptable cabin pressure swing

Mon Feb 29 05:02:46 EST 2016

With regards to the valve coming unseated, or dislodging.  I made mine with
a wing nut on the shaft.   Means I can adjust the cracking pressure, and
bolt it tight in the event of a leak or excessive flow, such as towing.  It
feels a little vulnerable on the top and I wish id put a guard around
it.   Could have had a few more holes as well.   I have a dome that is only
retained at the edge, so I need the valve.  But, I am in agreement with
Hank, in the event of an uncontrolled ascent and overpressure situation, im
not sure it would vent quick enough.  I now have a high power compressor
that Hank gave me that vents outside at the flick of a switch.  I much
prefer this. Pics attached.

kind regards
James

On 28 February 2016 at 18:45, Alan James via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> G.L. says that "pipes leading through the pressure hull wall are to be
> fitted
> with two shut off devices, one of which is to be located immediately at the
> hull wall"
>    So the overpressure valve would be one valve & G.L. would require one
> more.
> Alan
>
>
>
> ------------------------------
> *From:* Sean T. Stevenson via Personal_Submersibles <
> personal_submersibles at psubs.org>
> *To:* Personal Submersibles General Discussion <
> personal_submersibles at psubs.org>
> *Sent:* Monday, February 29, 2016 7:03 AM
>
> *Subject:* Re: [PSUBS-MAILIST] Acceptable cabin pressure swing
>
> The requirements only state that some means be provided of equalizing
> pressure on both sides of a hatch prior to opening. To me, this reads like
> something as simple as a small diameter needle or ball valve connecting the
> two sides, as there is no particular requirement for speed of equalization,
> and in fact the smaller flow area is safer in the event of something
> leaking.  The rules indicate that no possible failure by design should be
> capable of raising the interior pressure 1 atm, so really, the only reason
> to need a high volume OPV is if some lower pressure than that caused by
> some sort of failure could potentially unseat a dome, hatch or other
> fixture with limited capability to withstand internal pressure, in a way
> that is both potentially dangerous and can't otherwise be addressed in
> design.  The other possibility is if you want to accommodate a salvage
> blowdown at depth as a flooding control measure, and then be able to v! ent
> that excess pressure on the way up, in which case a high flow valve is
> helpful, but I would still pay particular attention to how one might
> accommodate a failure of such a valve to reseat.
> Sean
>
>
> On February 28, 2016 8:57:54 AM MST, hank pronk via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> 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 b! e 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] Accep! table 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_Subme! rsibles [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 ed! ge 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,          W! here 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 -0600
> Jon 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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