[PSUBS-MAILIST] Acceptable cabin pressure swing

Mon Feb 29 08:36:08 EST 2016

I'd be interested to learn more about that compressor. Is that the same as the one Hank has in Gamma, or something different?

On the relief valve, I suppose one could make it code compliant by piping your cabin air to it through a shutoff, versus simply allowing the cabin air to flow through. Would have to be a big valve to get the flow you need though.

Have you done a test to see how much internal pressure it takes to unseat the dome?  Also, how quickly can that compressor drop the cabin pressure?

Sean

On February 29, 2016 3:02:46 AM MST, James Frankland via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>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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