[PSUBS-MAILIST] O2

Fri Jan 31 09:54:48 EST 2020

As was done of the early Perry lockout boats and the JSLs for mixed gas storage--

-----Original Message-----
From: Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org>
To: personal_submersibles <personal_submersibles at psubs.org>
Sent: Fri, Jan 31, 2020 9:35 am
Subject: Re: [PSUBS-MAILIST] O2

There's always the option of custom designed gas storage vessels (spherical?), but then you'd need to certify them, and would need a transfer / booster pump to fill them.

Sean

-------- Original Message --------
On Jan. 31, 2020, 07:11, via Personal_Submersibles < personal_submersibles at psubs.org> wrote:

Yup, me too.
I just thought the visual of squashed scuba tanks might be entertaining.
Not all get squashed, though. I think Alvin has titanium air bottles. Which cost, I assume, about as much as an average plug--EACH!
Vance

-----Original Message-----
From: Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Thu, Jan 30, 2020 11:39 pm
Subject: Re: [PSUBS-MAILIST] O2

I agree with you Vance but that doesn't apply to the majority of the subs the Psubs group are building. I just don't like HP gas in a one atm sub if it can be helped, that's all.Rick
On Thu, Jan 30, 2020 at 4:17 PM via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Okay for shallow subs, Rick, not for deep. HP bottles don't much care for external pressure--will collapse at 3000 psi external (once empty). Alvin, Nautile, and others of the deep diving community (including P4, 5 & 6) all carry their primary HP oxygen storage internally. They have to. Not a psubs issue, obviously, unless your name is Scott Waters. the secondary O2 bank is external on P6 but if these bottles were ever depleted at depth, they would probably have to be replaced after the fact. HP air is different, as they can't be depleted beyond whatever the external pressure is. Oxygen bottles? Not so much.Vance

-----Original Message-----
From: Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Thu, Jan 30, 2020 8:41 pm
Subject: Re: [PSUBS-MAILIST] O2

I personally don't believe HP gas has a place inside a one atm sub. I know ketteredge did it but still don't think it should be for three reasons. 1. allows a lot more room in a small confined space, 2. could raise the ppo2 to a fire hazard level before you could secure the problem and 3. You are going to increase your internal pressure much faster and greater if it is HP rather than LP and the least internal positive pressure pushing the wrong way against the ports and hatch seal while ascending, the better.Reaction time is effected when something like a hose lets go so you may increase internal pressure faster than one might think. I was being pushed down to 700' in SAT on a job and all the condiments that are put inside (salade dressing, ketchup, etc) is supposed to have a hole poked in the top by the tenders and they forgot to do that on a bottle on salad dressing we were using. We were eating dinner while being pressed and the last guy to use it screwed the top on all the way thinking that a hole had been put in it like normal and it imploded while it was sitting right next to me. It took some time to get our witts about us as we thought a port had let go but other than being covered with broken glass and thousand island dressing, everything was ok. I am keeping all my HP gas outside.Rick

On Thu, Jan 30, 2020 at 3:04 PM David Colombo via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hi Hank, I am using 5 E size tanks (20cf) in the SeaQuestor. They sit right behind my pilot seat within arms reach. Each are individually valve controlled. Though they are tied to a manifold that holds the digital gauge tied to my plc, so that I only have one digital gauge. No more than one tank at a time would ever be open. Indivudually they have their own digital gauge and flow control, in addition to the digital gauge on the manifold.  This gives me the ability to disconnect a bottle from the digital system in the event the plc goes down, and still control its flow and have the ability to read the tank level. I'm all about redundant systems.Best Regards,David Colombo
On Thu, Jan 30, 2020, 12:39 PM Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

It is possible to employ burst devices in place of the standard cylinder burst discs which similarly protect the cylinders, but allow for plumbing the exhausting gas overboard instead of venting it into the cabin. Quieter too.

Sean

-------- Original Message --------
On Jan. 30, 2020, 11:04, Alan via Personal_Submersibles < personal_submersibles at psubs.org> wrote:

Alec,I have seen one tank empty out. The burst disk went on one of a bunchof tanks we had for a dive trip. It was about 8am so no heat from sunlight to increase pressure.A really loud hisssss for ages. Would sure get you panicking.Alan

On 31/01/2020, at 3:33 AM, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Yes, fire as in the Apollo 1 scenario. It's really a hard ABS requirement to meet, because you're already at 21% O2 under normal conditions so any one tank can't contain more than 2% of the cabin volume in O2. I think you'll find that implies the tanks need to be absolutely minuscule. On the plus side, as you say it would take a really, really unusual failure to empty a tank. Make sure the tank valves are readily accessible and not hidden behind anything, and make it a documented SOP for them all to be closed except the one currently discharging.
On Thu, Jan 30, 2020 at 9:22 AM hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Alec, good point, so the risk with that is fire?  In my case, with separate bottles not inter-connected the tank would have to fail or the regulator.  I love simpleHank
  On Thursday, January 30, 2020, 7:02:22 AM MST, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote: 

Hank,
In addition to the 1 atm rule Sean mentioned, there is a second requirement. The uncontrolled release of the contents of one tank of O2 should not raise the cabin O2 content above 23 percent. This second condition I suspect you will find more onerous than the first.
Best,Alec

On Thu, Jan 30, 2020 at 8:31 AM Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Plumbing all of your oxygen cylinders into a manifold using check valves should suffice. The idea being that any single failure should not empty the entire bank, and the individual cylinders need to be small enough to keep the total pressure increase below 1 atm if you do happen to lose one. 

Examine your entire plumbing system, identifying every connection and the consequences of it failing. Either the consequences need to be acceptable, or you have to have a response plan for that failure. 

As far as corrosion protection for through hull fittings, if you overlooked something in design, plating or cladding with corrosion resistant materials can be an option. At work, I have some vessels that I designed in A105 steel (similar to A516 gr 70, but forgings), that I am sending out to have the fluid exposed surfaces clad with Inconel 625 for corrosion resistance. Of course, I'm dealing with much worse stuff than seawater: hydrogen sulphide-saturated acidified high salt brines at elevated temperature. Still, it's always worth a look at costs of such processes versus the lifetime cost of maintenance. I was expecting the cost of cladding to be far higher than the quote I received. On the other side of the coin, I have some parts in the same system with deep holes that can't possibly be clad or painted, so I had to have them machined out of Hastelloy C276. One 8" end cap is worth more than my truck.

Sean

-------- Original Message --------
On Jan. 30, 2020, 06:04, hank pronk via Personal_Submersibles < personal_submersibles at psubs.org> wrote:

Sean, okay that is where I missed the boat.  I know about the do not exceed 1 atm rule but did not realize it meant a single tank.  If I lost all my O2 it would be a problem.  I am using multiple tanks so all is good.   I do not have room to drill out the steel plus changing an O2 tank would really suck with this new body. Forget about a change if the sub is in the water.Hank
  On Thursday, January 30, 2020, 5:12:49 AM MST, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote: 

Nothing wrong with internal tanks as long as you can prove by calculation that the unintended release of the contents of any single cylinder (provided they are individually valved - hard plumbed manifolded cylinders where a single failure would empty them all would need to be considered together as one) will not raise the pressure of the occupied space by more than 1 atm.

Through hull shouldn't be a big deal either. Drill larger if necessary, and use a stainless insert.

Sean
-------- Original Message --------
On Jan. 30, 2020, 04:58, hank pronk via Personal_Submersibles < personal_submersibles at psubs.org> wrote:

Hi All, here is an interior picture of Limiting Factor that shows what appears to be O2 tanks.  I thought it was not an approved practice to have that much compressed gas onboard.  My original design in E3000 was to have external O2 supply but I prefer internal.  I messed up in two ways.  First off I provided a steel penetrator opening for O2.  The other screw up is when I built the new body I completely neglected access to change out the tank.  So I am going with internal tanks unless someone can talk me out of it.  Hank
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