[PSUBS-MAILIST] Acceptable cabin pressure swing

Mon Feb 29 09:09:06 EST 2016

didn't answer all the questions...

No, I haven't tested how much pressure will blow off the dome, nor am I
going to.  The dome is held on with an aluminium retaining ring and 24
(ish? cant remember) M6 bolts.  I wouldn't want to damage the dome or the
ring in a test.  It was very awkward to machine the ring.  I just keep a
close eye on cabin pressure.

Flicking the compressor on instantly reduces cabin pressure.   Ive never
let it get to more than about 1/4psi over, but a 3-4 second burst on the
compressor gets rid of that.

I find I tend to get a little overpressure before the scrubber kicks in
properly.   Once CO2 has stabilised I don't really need to fiddle with
anything.  It just sorts itself out.

Its also handy for a pre launch vacuum test.

regards
James

On 29 February 2016 at 13:58, James Frankland <jamesf at guernseysubmarine.com>
wrote:

> 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
>>>> _______________________________________________
>>>> Personal_Submersibles mailing list
>>>> Personal_Submersibles at psubs.org
>>>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>>>
>>>> _______________________________________________ Personal_Submersibles
>>>> mailing list Personal_Submersibles at psubs.org
>>>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>>>
>>>> _______________________________________________
>>>> Personal_Submersibles mailing list
>>>> Personal_Submersibles at psubs.org
>>>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>>>
>>>>
>>>> _______________________________________________
>>>> Personal_Submersibles mailing list
>>>> Personal_Submersibles at psubs.org
>>>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>>>  _______________________________________________ Personal_Submersibles
>>>> mailing list Personal_Submersibles at psubs.org
>>>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>>>
>>>> _______________________________________________
>>>> Personal_Submersibles mailing list
>>>> Personal_Submersibles at psubs.org
>>>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>>>
>>>>
>>>> ------------------------------
>>>>
>>>> Personal_Submersibles mailing list
>>>> Personal_Submersibles at psubs.org
>>>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>>>
>>>>
>>>> _______________________________________________
>>>> Personal_Submersibles mailing list
>>>> Personal_Submersibles at psubs.org
>>>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> Personal_Submersibles mailing list
>>>> Personal_Submersibles at psubs.org
>>>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>>>
>>>>
>>> ------------------------------
>>>
>>> Personal_Submersibles mailing list
>>> Personal_Submersibles at psubs.org
>>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>>
>>>
>> _______________________________________________
>> Personal_Submersibles mailing list
>> Personal_Submersibles at psubs.org
>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20160229/5aae61e7/attachment-0001.html>