[PSUBS-MAILIST] Acceptable cabin pressure swing

Mon Feb 29 08:58:12 EST 2016

Hi Sean,

Its the baby brother of Hanks.  Same thing but a bit smaller.  Cornelius
Compressor.  Googling a bit, it seems they came out of WW2 era aircraft and
were used for moving gun turrets.

24v.  Pumps to 1500psi.  I have it T'd into the aft main HP line with a
check valve inline.

That's about all I know about it, but it seems really good.

Regards
James

On 29 February 2016 at 13:36, Sean T. Stevenson via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> 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, Bri! an 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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