[PSUBS-MAILIST] Scuba Tank Purchase Questions

Thu Feb 20 16:21:43 EST 2020

This is only possible with 200 / 232 bar DIN valve outlets, because they are shallow enough to accommodate a SCUBA yoke (CGA 850) over the valve pillar. So-called 300 bar DIN valves are identical to the 200 / 232 bar type with the exception of being slightly deeper, with (IIRC) seven full threads of engagement, but you can't get inserts for them because most SCUBA yokes won't fit over them.

The benefit of the DIN is of course that the O-ring is actually captive within a gland on the male end, and so is much more resistant to extrusion than the CGA 850 connection. For diving, I use the deeper (300 bar) DIN connections wherever possible, because a diving regulator first stage DIN stem will seat fully into them and doesn't leave a gap between the DIN handwheel and the valve pillar, which can be an entrapment hazard. For sub applications, this is probably less critical.

In any case, saliva should not be used as an O-ring lubricant. Valve to regulator O-rings are intended to be static in service and do not need to be lubricated, although doing so can extend their service life because rotary motion when tightening the connection can precipitate failures of the elastomer. The tradeoff is that the O-rings are more prone to extrusion when lubricated, and are also prone to attract and retain particulate contaminants when exposed. If you choose to lubricate, do so with a proper oxygen-compatible performance lubricant (e.g. Christolube), just as you would with dynamic O-rings, and use only enough lube to make it shiny.

Always have spare O-rings on hand, and make sure you have a set of brass or plastic O-ring picks / extraction tools which are soft enough to not scratch the sealing surfaces when you go to change out a seal.

Sean

-------- Original Message --------
On Feb. 20, 2020, 13:44, Alec Smyth via Personal_Submersibles wrote:

> Hi Steve,
>
> I concur with everyone else regarding DIN. But one thing to point out is that modern DIN fittings come with a little screw-in adapter that turns them into yoke fittings. So in the event you needed to grab a tank and put an old regulator on it, you can still do so.
>
> Best,
> Alec
>
> On Thu, Feb 20, 2020 at 3:16 PM Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>> Hank,
>> Just wondering, with those O-ring failures mentioned, were you travelling
>> with the tanks fitted on your sub & yokes on?
>> If so there might have been a lot of rotary movement on the dry O-rings while
>> bumping around on a long trip.
>> Alan
>>
>> On 21/02/2020, at 9:08 AM, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>
>>> Steve,
>>> most o-ring failures are on the surface, & you will hear a leak straight away.
>>> When they leak under water it is normally a slow leak.
>>> It's recommended that you look at your O-ring as part of a pre dive check.
>>> Some divers spit on them prior to assembly to grease them up a bit.
>>> The O-rings are normally replaced in an annual visual inspection.
>>> Maybe just make sure you have new O-rings & carry spares.
>>> 10s of thousands of divers are using them & they are a lot more vulnerable
>>> than you who will be using them for blowing ballast.
>>> Great Escape was a great movie. You could have named it "The Blob"
>>> Alan
>>>
>>> On 21/02/2020, at 8:30 AM, Steve McQueen via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>
>>>> Thanks. Didn't realize yoke O-rings were such an issue. This changes my mind on my valve choice.
>>>> Appreciate reviewing this topic.
>>>>
>>>> Steve
>>>>
>>>> On Thu, Feb 20, 2020 at 2:23 PM T Novak via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>>
>>>>> Just a case in point about DIN versus yoke, during the Flathead Lake expedition we blew two yoke O-rings on the Gama scuba tanks. It goes without saying that spare O-rings are a necessary inventory item to have on hand during sub ops.
>>>>>
>>>>> Tim
>>>>>
>>>>> From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of Cliff Redus via Personal_Submersibles
>>>>> Sent: Thursday, February 20, 2020 10:25 AM
>>>>> To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
>>>>> Subject: Re: [PSUBS-MAILIST] Scuba Tank Purchase Questions
>>>>>
>>>>> Mine are aluminum for primary and I have a composite tank internal as a backup HP source.
>>>>>
>>>>> With a name like yours, you could not find a better boat name.
>>>>>
>>>>> Cliff
>>>>>
>>>>> Sent from my iPhone
>>>>>
>>>>>> On Feb 20, 2020, at 10:57 AM, Steve McQueen via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>>>
>>>>>> 
>>>>>>
>>>>>> Cliff, thanks. Good to hear about actual field issues. I will reconsider my thoughts a.ccordingly.  I have completed my contribution for Pisces VI and have refocused on finishing my project. Having your own compressor is a nice advantage. Are your MBT HP tanks aluminum or steel?
>>>>>>
>>>>>>  My K-250 is named "The Great Escape" (get it?).
>>>>>>
>>>>>> Steve
>>>>>>
>>>>>> On Thu, Feb 20, 2020 at 11:36 AM Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>>>>
>>>>>>> Steve, if it were me, I would go with DIN fitting on scuba tanks.  About 2 years after I built my boat I had an O-ring blow while I was on the boat ramp ready to launch. If this would have happened during a dive, I would not have been unable to blow my MBTs by myself.  I would have had to have divers to manually inflate my MBT with open vent ports.  My experience is that most scuba shops can fill scuba tanks with DIN connections.  After the incident, I switched my MBT HP air supply to DIN values and have never had any trouble since then.  Also, last year I purchased a portable scuba compressor that came with an adapter to let you fill Yoke or DIN valves.  Also this compressor is capable of filling a steel HP tank if I want to.  To me, the real benefit of steel tanks with DIN connections is the ability to fill to a higher pressure.  If you don't need the higher pressure, then aluminum are lower cost.
>>>>>>>
>>>>>>> We are all looking forward to your sea trials for your lime green K250.  I love the paint job on your boat.  Has she got a name yet?  I am surprised you have had any time to work on your boat with the PLC work you been doing for Scott on his Pieces 6.
>>>>>>>
>>>>>>> Looking forward to catching up with you this year at one of the psub events.
>>>>>>>
>>>>>>> Best
>>>>>>>
>>>>>>> On Thursday, February 20, 2020, 09:54:59 AM CST, Steve McQueen via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>>>>>
>>>>>>> All, getting ready to buy 2 scuba tanks for my K250. Just wanted to see if anyone had an opinion of my thoughts?
>>>>>>>
>>>>>>> 1) Choosing steel vs. aluminum (prefer its weight/buoyancy characteristics)
>>>>>>>
>>>>>>> 2) While I was wanting as much air volume as possible I decided against a HP version as I have heard most places won't (can't?) fill to that capacity anyway
>>>>>>>
>>>>>>> 3) Deciding on standard pressure steel 80s with K-valve (yoke fitting)
>>>>>>>
>>>>>>> I've been watching for a while (including Black Friday) but it seems there isn't much mark up and these tanks don't appear to go on sale.
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>> Steve
>>>>>>>
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