Twin manifold plugs

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I guess for the record I should disclaim and state - Despite my comments in this thread - Retailers have specifically recommended that DIN sealing plugs should NOT be used on high F02 cylinders. See Twin manifold plugs

I got curious and looked around a bit ... DGX makes almost the exact same statement for their (equivalent? - same?) plug (DGX HP Sealing DIN Plug | Dive Gear Express®), but interestingly not on their push-button plug (DGX HP Sealing DIN Plug w/Pressure Release | Dive Gear Express®) - by intent or omission, I don't know, but the push button one is only listed as Nitrox ready.

- Of merit, DGX provides a much more thorough explanation of the issues of releasing pressure with a pressurized, plugged valve. Worth checking out. -

Serious question for others out there - Is this "standard" received wisdom, something from the manufacturer's lawyers as a CYA, or from the folks that deal with high FO2 as hands on experts.

I am dubious about the relative risk of the impact claim as both the burst plug and valve mechanism are also vulnerable to impacts and exposed to the gas at full pressure, all the time.
Obviously, it is much easier to keep the internals of the cylinder and valve clean, than the DIN socket and plug. So in that regard, yes, the risk is relatively higher, but also applies when a reg is on there and pressurized too.

As for the venting/friction the same sorts of mechanical processes are also present during cylinder filling with whipping/boosting and venting. Again, hopefully in a meticulously clean environment.

I think it really comes down the relative risk of being seriously O2 clean and plugged vs The risk O2 jetting out into a confined, potentially fuel rich environment.

Maybe I am very wrong in my thinking about the relative risks ...

Ok starting from the top...

A non-venting SS DIN plug used in a high fO2 environment is not a great idea. The plug actually damages the threads in the DIN fitting because there is a ****load of friction if there is pressure behind it - hence needing a big wrench to undo it. Is that risk more or less than venting an AL40 of O2 into your car? Hard to say, neither happens often enough to develop a risk profile.

The venting plug is not "o2 cleaned" and DGX doesn't want to vouch for those convoluted passages being "o2 safe" BUT they mostly mitigate the high pressure O2 locking the plug into the valve if the knob gets bumped. You may still need a wrench and light force to remove it because the oring gets wedged into the sealing surface. But no massive friction forces involved.

DIN fill whips are fully vented prior to removing, and the DIN fitting itself provides enough leverage to remove it (moreso than the plug) hence you never need a wrench to remove these unless that valve is really corroded.

The mass of O2 behind a DIN plug is quite small and there has never been a publicized DIN plug O2 fire. There have been fires from accidentally turning on O2 tanks abruptly. Also fires from trying to remove a valve from an O2 tank while pressurized. Make of that what you will.

PS the Delrin and plastic plugs are awful. Yes they have a vent hole "in theory". They can and have shattered when pressurized sending grenade like plastic fragments into a diver's hand more than once because the hole is too small or the material too weak or the pressure is too high or all of the above. Either use a SS plug (venting or not as you see fit) or don't use a plug at all.
 
I’ve been told of divers whose hands have been badly damaged from exploding fragments of the plastic/delrin plugs. Metal only has been strongly recommended.

Got beaten
 
Look, these are all cases of weighing relatively remote risks. It's hard to get real numbers.

But the reason why you aren't supposed to use a sealing plug with no pressure release mechanism with 100% O2 is that you might have to use brute force to rotate a tightly fitted screw thread in a 100% O2 environment at 3000 PSI. That doesn't happen with cylinder filling, whipping or boosting. Those DIN threads are screwed and unscrewed at ambient pressure.

Ok starting from the top...

A non-venting SS DIN plug used in a high fO2 environment is not a great idea. The plug actually damages the threads in the DIN fitting because there is a ****load of friction if there is pressure behind it - hence needing a big wrench to undo it. Is that risk more or less than venting an AL40 of O2 into your car? Hard to say, neither happens often enough to develop a risk profile.

The venting plug is not "o2 cleaned" and DGX doesn't want to vouch for those convoluted passages being "o2 safe" BUT they mostly mitigate the high pressure O2 locking the plug into the valve if the knob gets bumped. You may still need a wrench and light force to remove it because the oring gets wedged into the sealing surface. But no massive friction forces involved.

DIN fill whips are fully vented prior to removing, and the DIN fitting itself provides enough leverage to remove it (moreso than the plug) hence you never need a wrench to remove these unless that valve is really corroded.

The mass of O2 behind a DIN plug is quite small and there has never been a publicized DIN plug O2 fire. There have been fires from accidentally turning on O2 tanks abruptly. Also fires from trying to remove a valve from an O2 tank while pressurized. Make of that what you will.

PS the Delrin and plastic plugs are awful. Yes they have a vent hole "in theory". They can and have shattered when pressurized sending grenade like plastic fragments into a diver's hand more than once because the hole is too small or the material too weak or the pressure is too high or all of the above. Either use a SS plug (venting or not as you see fit) or don't use a plug at all.

I’ve been told of divers whose hands have been badly damaged from exploding fragments of the plastic/delrin plugs. Metal only has been strongly recommended.

@doctormike, to your point, the threads are actually not exposed to pressurized O2, at first. But, (and I didn't fully consider the likely pressure profile due to the M-F thread "tightness") once you crack it yes, the threads become flooded with O2 at essentially full pressure. If you continue to crank it out past the just-cracked point continued friction + HP O2 = could be bad.

@rjack321 Great point about the thread damage and mitigation of the push button plugs. I agree on the the low mass of O2, of course maybe the lack of known incidents is more about few O2 tanks being plugged ...

I'm think some empirical testing is in order - maybe this summer around the 4th, in case I get some positive results. :cool:

@rjack321 & @Marie13 Now you have me thinking about just getting a pile of these and chucking my non-metal plugs altogether. (I knew they existed but haven't seen them available to buy before) Dust Cap for DIN Valve, Black Vinyl | Dive Gear Express®
dx-70139_1.jpg
 
@doctormike, to your point, the threads are actually not exposed to pressurized O2, at first. But, (and I didn't fully consider the likely pressure profile due to the M-F thread "tightness") once you crack it yes, the threads become flooded with O2 at essentially full pressure. If you continue to crank it out past the just-cracked point continued friction + HP O2 = could be bad.

It's not that complicated, and it's the reason why more than one retailer strongly recommends NOT using sealing DIN plugs with 100% O2.

If you have a sealing DIN plug in place on an O2 tank, and you open the valve, you have now created a space (1) filled with 100% O2, (2) at tank service pressure, and (3) that can only be opened by brute force involving heavy metal on metal shearing with friction.

If you didn't believe the first page I quoted, here is another one, from Divegear Express.

"We do NOT recommend the use of any type of HP sealing DIN Plug with oxygen rich gas mixtures, as impact or the friction of loosening the plug against high pressure oxygen could cause ignition, fire, and explosion leading to injury or death.

A dangerous condition exists if the plug has been pressurized by inadvertently opening the valve. No amount of force by hand will move it. First you MUST tightly close the valve, and only then you MUST loosen the plug with a wrench VERY SLOWLY and stand clear of the plug as you turn the plug in the valve. Make sure the plug is "aimed" at something able to withstand the force of ejection and no part of your body is in the path the plug might take if it is forcefully ejected. Back the plug out of the valve one full turn, but no more, this is enough to break the O-ring seal. Gas will gradually leak out around the threads until eventually the plug is loose enough to turn by hand, however even then we recommend continuing to use the wrench to turn the plug. If you do it slowly enough, you will hear a "hiss" and then a soft "pop" as the plug is ejected and falls to the floor.

If you find the plug and valve pressurized for no apparent reason and the valve is not found to be opened, it's very possible the valve has been leaking and the leak has been stopped by the plug. In this case, there is no quick way to remove the plug without extreme hazard because you are unable to determine the magnitude of the valve leak while the plug is in place. We recommend you take the cylinder to a cylinder hydrostatic testing facility for assistance removing the plug."
 
...
If you didn't believe the first page I quoted, here is another one, from Divegear Express.
...

Yep,
...
I got curious and looked around a bit ... DGX makes almost the exact same statement for their (equivalent? - same?) plug (DGX HP Sealing DIN Plug | Dive Gear Express®), but interestingly not on their push-button plug (DGX HP Sealing DIN Plug w/Pressure Release | Dive Gear Express®) - by intent or omission, I don't know, but the push button one is only listed as Nitrox ready.

- Of merit, DGX provides a much more thorough explanation of the issues of releasing pressure with a pressurized, plugged valve. Worth checking out. -
...
 
I bought this setup from my local dive shop and it will be here in a week. I was wondering for people who have also bought this exact setup. Does it come with plugs for the valves so I can use them in a single tank setup? Or do I have to buy plugs separately. I want to get them on order now so I have them if I need to buy them. I looked everywhere and can’t find anything saying if this comes with them or not. If you look at just the manifold itself in the xs scuba catalog it shows them coming with plugs, but I can’t find anywhere saying this double setup comes with them.

HP Faber Hot Dip Galvanized Doubles Package

This here is the OP he wants to make his double into singles by removing the center and using plugs. What have you all been posting about?
 
This here is the OP he wants to make his double into singles by removing the center and using plugs. What have you all been posting about?

Don’t look at me. I got it right. :D
 
For big trip I stack a ton of cylinders in my truck. In my CCR O2 & deco bottles I put in my venting plugs (I have a couple) or I loosely install a nonventing plug. It is not that hard to wack a DIN opening out of round and then the whole valve is useless. SS plugs keep the opening intact. I never use DIN plugs to keep DIN threads clean. Those threads are all corroded anyway. I also don't O2 clean DIN plugs, although I did soak mine in phosphoric acid last fall to get the rust off them - mine are all 15+ yrs old and 304 stainless actually does rust.
 

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