EAN40 Tank Valve Thread Lube

[Tracy]

Happy...again after sifting through your post...agree "to each their own"....check this out, Catalina recommendations...https://www.youtube.com/watch?v=jIRc3Joa0Ak&t=331s&ab_channel=AlecPeirceScuba...

Not saying that lube is the only way to go, but over many years it has worked for me...personal choice.

Free advice [worthless in fact]....don't start drinking, stick to your chemicals ...

Googled as you suggested...nothing on tank valve threads that I could find....no big deal and not consequential.

That bulletin is close to 30 years old. They haven't recommended that since Nitrox came to market.

 

[Wallowa]

I am not trying to refute or correct how anyone decides to install the valve into the tank......https://www.divegearexpress.com/library/tek-tips/valve-lube.....describes the reason for lube was galvanic corrosion and they say that now [higher oxygen% use] that use of lube on threads is "debatable"...with high oxygen percentages became the popular norm use of the 'wrong lube' could result in bad things happening if above EAN40....galvanic corrosion/galling of threads in aluminum tanks is real and I am guessing this corrosion would be accelerated in the presence of higher oxygen %.....be that as it may why not use a correct lube on the valve dependent on the oxygen %? Established that up to EAN40 no special lube is needed...in passing, speaking of lubes, my understanding was and is that lube is not used on static o-rings but a slight amount is used on dynamic o-rings. Use lube on a static o-ring and chance it being extruded under pressure.

Again, I am not trying to influence how anyone handles their dive gear. It is your gear, you make the choices. Only would like to exchange points of view. I appreciate divergent views.

 

[Tanks A Lot]

The lubrication debate is an old one in the SCUBA industry. I want to be clear that both lubricating threads and not doing so have advantages. The advantages of not lubricating outweigh the advantages of lubricating them for me. I do not lubricate threads and have advised students not to do so either.

Advantages of lubricating:​

Protects the chrome and aluminium to some degree.​

Especially aluminium is a pain with galling under high axial loads. Unfortunately, lubricating nearly doubles the axial load at the same torque value, so this advantage is minimal at best.

It can counteract galvanic corrosion.​

This point is nearly universally misunderstood by the diving community. Galvanic corrosion heavily depends on the relative sizes of the cathode (cylinder) and anode (valve) in contact with the electrolyte (water). The little dab of grease people put on the leading threads completely misses the mark. While this might help to some degree, coating the base of the valve and the dip tube are equally important. Catalina or Luxfer, I can't remember which one, acknowledges this in their manual. There was an interesting study back in 1978 that confirms this. Using plastic dip tubes or coating the base and dip tube in grease is key, not just coating the threads. It's one of those things I see nearly every single technician get wrong.
If you do some back-of-the-hand calculations, which I admit may be off by a good amount, the axial load of 95Nm and the force of the cylinder pressure will squeeze the grease to a thin film, probably 0.001mm. At this thickness, Molykote 111 would provide protection of 15V, which is still impressive! However, I suspect that at those thin films, the roughness of the threads themselves plays a major role, and the grease might be confined to valleys. It will surely provide some benefit, but I'm unsure how much there really is left.

​

Disadvantages of lubricating:​

Torque gets distorted to a high degree.​

At 95Nm torque, the axial load on an M25x2 valve will be roughly 1100Kgf. In a lubricated state, the axial load will jump to nearly 2000Kgf. This is a significant increase. While grease might counteract some corrosion, it doesn't prevent it. The deposits that develop now develop between threads at twice the axial load. Greased threads on cylinders that have gotten wet have, without exception, been more of a pain for me to loosen than unlubricated ones. The reason is the resulting higher axial load and the grease's slight loss in "greasing ability" once grit develops.

Grease attracts rubbish.​

Cleaning out grease from threads is hard, really hard... To get them clean, you have to sit there with some alcohol and a brush soaked in it and really get into it. No shop I ever visited does so, even though most are well aware of it. And not cleaning out grease attracts rubbish, which gets caught in it. If you are unlucky, the threads pick up enough debris on the way into the cylinder that, instead of preventing galling, you kickstart it in a snowball effect. Unlubricated threads are way, way easier to keep clean.

Lubricating can promote corrosion.​

I know I said earlier that it might prevent corrosion, but before you get the pitchforks out, hear me out. When you apply a small dab of grease to the lower threads of the valve, there is virtually no grease left whatsoever on the lower threads once you finish screwing it in. In the picture below, I smeared a few, for me at least, humongous dabs of grease, yet there isn't anything left to see, especially where the "opening" of the thread is, which leads into the upper threads.

This presents a particular problem because moisture can and will sometimes enter the lower threads. For some reasons that I must admit I don't fully understand, moisture does get trapped sometimes. I believe it has to do with little air circulation in this area, but I must admit I'm not sure. This concentration of moisture in one particular spot leads to the formation of deep pits. The rejection criteria for pits in the threads are far more stringent than general corrosion. While unlubricated valves do suffer corrosion in the lower threads, they do so evenly. Lubricated threads, on the other hand, show deep pits forming.
I was in the lucky situation of being able to test this with customer tanks (Thank god for some that I can count on skimping on compressor service and that were guaranteed to pump wet...). The lubricated threads almost always have done worse than the unlubricated ones. The only exception I ever encountered to this was a batch of cylinders that ingested copious amounts of saltwater.

The right grease is not always used:​

I know this might not be a fair point, but it seems relevant enough to me, as I encountered it more than I would like. If you use something like Molykote 111, I know it has some advantages as outlined earlier, despite its disadvantages. But unfortunately, people see others use grease and, if they have nothing else on hand, use the next best thing. I have had customers grease their threads with marine outboard grease (Great in a breathing apparatus, I assume!) to Vaseline, which dried out and had me huffing and puffing upon valve removal. This point is not entirely fair, but somewhat relevant.

Grease has no place in an oxygen environment whatsever:​

While greases like Krytox or Christolube are more resistant to high O2 levels and pressures, they are far from immune to ignition. The absence of grease is just harder to ignite than a dab of Krytox because nothing just doesn't ignite - ever. Oxygen-resistant greases, on the other hand, can and do ignite if other factors compound.


If you grease your threads, I suggest you not only grease the threads but pay particular attention to the dip tube and base of the valve. Better yet, swap the brass tube for a plastic tube. Also, mind your torque values, as grease will increase axial load by nearly twice as much. Upon valve removal and insertion, you should also be diligent in removing any traces of old grease, as they will trap debris.
If you adhere to these things, greasing may make sense in that it protects from galling and potentially galvanic corrosion. On the flip side, you may trap moisture in the lower threads, promoting pit formation.

Personally, I feel like there is no winning to be had. Both sides have advantages and disadvantages over the other. But due to how things are implemented in the industry, I feel like not using grease is the lesser of the two evils.

---

With regards to O-ring greasing, the debate is equally an old one. What I want to leave you with is that even the static O-rings are not truly static.

Take an M25x2 valve, for example; the O-ring will overfill the gland by 0.23mm to 0.93mm, depending on the manufacturing tolerances. What this means is that the last bit when you insert the valve, you compress the O-ring. But you are not just compressing it; you are also turning the valve. This, in turn, will result in different torsional forces upon the O-ring. Without lubrication, you risk abrading the top and/or bottom of the O-ring.

And the O-ring is still not done moving. Upon pressurization, it moves from that compressed state against the outer walls of the gland.
Uncompressed:

Compressed:

While I must admit I have drawn this over-dramatic, the O-ring will always move a tiny bit with pressure changes, even a static one. Leave alone the even more hilarious myth of using spit as a lubricant. Sure, it's better than no grease at all, I concede that... Folks that propagate the spit myth seem to want to have their cake and eat it too. Spit has either the disadvantage that it dries out, which I believe to be true, providing no ongoing lubrication, or it does not dry out, in which case it would introduce a source of corrosion, as it mainly consists of water.

The myth that grease promotes O-ring extrusion is unfounded. O-ring extrusion depends heavily on the durometer of the O-ring, as well as the tensile modulus of the elastomer in use. The tensile modulus of NBR, for example, would be in the region of 2.0 to 15.0 MPa. What this means is that it takes this amount of MPa to stretch the material to twice its original length. The higher the tensile modulus, the more resistant to extrusion the material will be, as it recovers better from localized forces.
In short, a high durometer correlates to a high tensile modulus, which correlates to higher extrusion resistance.

People often say that "feathered" O-rings are the culprit of lubrication. This is equally untrue. Feathering of O-rings is almost always due to an extreme overfill condition of the gland.

The SCUBA industry is unique with its myth of no lubrication of static O-rings; this is not practiced in a single other industry I can think of. Lubrication is extremely important in dynamic seals and very important in static seals during installation and somewhat relevant to final seating of the static O-ring.

Both of these topics are some of the most often debated and misunderstood topics when I talk to dive centers or teach students. I believe looking objectively at the facts can help to put one's own preconceived ideas aside. Especially the O-ring lubrication topic really is clear-cut, at least in every other major industry....

 

[Wallowa]

T.A.L. thanks for the information and taking the time to post it. Do appreciate you voicing your views. I have a few observations, they are only based on my experience and not as counter points. No challenges here, just me offering my opinions and what I have seen.

Not doubting your comments but threads on valve once screwed in should not be exposed to any moisture. SCUBA air is specified to be "dry" and yes that can be overcomed if compressor is in fact pumping in water vapor or if tank pressure is drained and valve is opened to outside air or water. Moisture does hasten galvanic metal transfer and oxidation. That is why we do VIPs.

Galvanic galling will occur with or without axial loading you mentioned; when dissimilar metals are placed together, tightening that contact also increases the galvanic transfer. Why you found threads with lube would corrode more that bare threads mystifies me.

O-ring extrusion does occur, especially when they are lubricated. I have seen o-rings extrude and get damaged as the valve it screwed into the tank even before the bottle was pressurized; add the deformation under high tank pressures and chance of extrusion jumps up. On older style Nikonos cameras o-ring could bulge/extrude if over lubed leading to leaks [lens and body]. In yoke style regulator connectors the captured o-ring if lubed will extrude, leak air and possible damage the 0-ring. Over lubricating leads to slippery o-rings on most of the extruded ones but any lube lowers the coefficient of friction.

I know nothing of 'tensile modulus of NBR' but have observed galling on straight threaded tank valves in aluminum tanks and extruded static o-rings. Both in my view could have been avoided.

Again my question: Why not put a correct [based on % oxygen] lube on tank valve threads to preclude the possibility of galling and for easy removal for VIPs/hydros? No need to lube base of valve or snorkel; galvanic corrosion requires metal to metal contact as with valve threads to tank threads.

As for lube "attracting" dirt/grit and contaminants; when used in a clean environment I have never found this to be an issue. I have found that cleaning off Dow 111 from threads of valve or tank easy.

Reviewing the literature the caveats against the use of lube in high pressure applications is for high oxygen % gases; most specifically with 100% oxygen. Use a lube that could combust in 100% at the tank pressures and ignition can happen . Normal compressed 21% air bottles and up to the rather arbitrary limit of EAN40 and contamination of a breathing gas is the issue, not combustion when lubes are in contact with the gas. As Nitrox proliferated undoubtedly so did the insurance costs for companies handling compressed gases or selling gear for divers. Lot of CYA happened. The threat of combustion is real but only when incorrect lubes are used with high % oxygen compressed gases.

In other applications the use of 'lubes' between dissimilar metals is call "Anti-Seize"; I view Dow 111 for use on my less than EAN40 bottle valves as just that, an anti-seize.

But hey, I could be wrong and each should make their own informed decisions....

 

[Tanks A Lot]

Part 1:​

Those are excellent points and the usual concerns voiced when I teach the subject. I try to address a few points:

[...]
SCUBA air is specified to be "dry" and yes that can be overcomed if compressor is in fact pumping in water vapor or if tank pressure is drained and valve is opened to outside air or water. Moisture does hasten galvanic metal transfer and oxidation. That is why we do VIPs.

I may have been unclear above, so I’ll try to clarify this a bit.

The only apparent advantage of using lubricant would be if the compressor pumps wet air. If only dry air is introduced, grease would provide no benefit at all, except perhaps preventing galling to some extent. This can easily be counteracted by using a lower torque value, say 40Nm to 50Nm, instead of the high 95Nm called for by ISO13341. Incidentally, the very same document explicitly states not to use any lubrication on the threads at all.

In stark contrast, the CGA, until recently, called for lubrication and a much higher torque of nearly 135 Nm. It now defers to the manufacturers.

Galvanic galling will occur with or without axial loading you mentioned; when dissimilar metals are placed together, tightening that contact also increases the galvanic transfer. Why you found threads with lube would corrode more that bare threads mystifies me.

The axial load does not influence the rate of galvanic corrosion. The rate is dependent on the standard electrode potential of the metals involved, as well as the surface areas of the anode and cathode in contact with the electrolyte. This is also the reason why it would be crucial to cover the base and dip tube. Catalina specifically emphasizes this point:

Apply a small amount of lubricant, Dow Corning Compound 111, to the end of the valve and the leading 2 to 3 threads of the valve.

I apologize if I made it sound like corrosion occurs more with lubrication than without. I may have worded this poorly. Let me try to rephrase it.

What often happens in shops that pump wet air is the following:

1. The compressor is in good condition and pumps dry air.
2. Service and/or filter changes are neglected, and it starts to pump wet air.
3. The wet air is noticed, and the problem is rectified, resulting in dry fills again. Jump back to step 1, and the cycle repeats.

I’ve often had customers who pump dry, then wet, then dry, then wet, and so on, over the span of several months. Crucially, there are often periods of dry, clean air followed by periods of wet, contaminated air.

Unlubricated threads allow moisture to enter freely. However, they also allow moisture to drain freely when dry fills are reintroduced. Unlubricated threads almost always develop gentle corrosion in threads 10 and lower. While not ideal, I can be more lenient with this kind of damage, as it sits low on the threads and often doesn’t interfere with the minimum required threads, which is usually 8 to 9 threads on aluminum cylinders.

On the other hand, lubricated threads mostly prevent moisture from entering the threads, that’s the whole point of lubrication. However, it doesn’t always fully prevent it, and when moisture does enter, it can get trapped due to the lubricant. This leads to isolated pits forming, and unfortunately, this is a kind of damage that is far more strictly scrutinized during visual inspections in the thread area. Once a pit spans two complete threads, the cylinder must be rejected. Trapped moisture can lead to this result, whereas I have never observed pits forming on unlubricated threads.

O-ring extrusion does occur, especially when they are lubricated. I have seen o-rings extrude and get damaged as the valve it screwed into the tank even before the bottle was pressurized; add the deformation under high tank pressures and chance of extrusion jumps up.

This is something I often hear, but only ever in the context of SCUBA, never in any other industry. I think you’re on the right track, but you’re blaming the wrong thing (lubrication) for the extrusion. Extrusion is always due to two reasons:

Excessive gap clearance​

O-rings are often modeled as a highly viscous fluid with very high surface tension. This viscous fluid (the O-ring) gets pushed by the pressure against the gland of the O-ring. Its high viscosity and surface tension prevent it from flowing through the gap clearance between the two workpieces. This gap clearance must be kept as low as possible to prevent extrusion, especially in high-pressure or dynamic applications.
Proper gap clearance:

But if the gap is too large, the viscous O-ring will start to flow through the gap and the O-ring fails by extrusion.
Excessive gap clearance:

Wrong elastomer​

The wrong elastomer means an elastomer that models as a less viscous fluid with lower surface tension. Ultimately, this is what tensile modulus represents. The tensile modulus depends on both the elastomer type and the chosen hardness. As a single factor, it is probably the best overall indicator of an elastomer's toughness. As an overview:

Material	Tensile modulus at 100% (MPa)
NBR (Buna-N)	2.0 - 15.0
EPDM	0.7 - 20.7
FKM (Viton)	1.4 - 13.8
EU (Polyurethane)	0.2 - 34.5
VMQ (Silicone)	~6.0

The wrong elastomer goes hand in hand with gap clearance. If you choose a high gap clearance, you must pair it with an elastomer that has a high tensile modulus. Conversely, tight gap clearances allow for the use of elastomers with very low tensile moduli. In high-pressure applications, it is routine to use backup rings, such as Parbak rings, which essentially reduce the gap clearance.

The damage you observed during installation is most likely due to one of the following:

1. Absence of Lubricant: Without lubricant, the O-ring is not able to glide smoothly into its resting place.
2. Extrusion During Installation: This is almost guaranteed to be due to an overfill condition of the gland, meaning the O-ring is too large for the gland.

 

[Tanks A Lot]

Part 2:​

On older style Nikonos cameras o-ring could bulge/extrude if over lubed leading to leaks [lens and body].

I'm not familiar with the Nikonos in particular, so take this with a grain of salt. What I would wager happened here is that the O-ring is made from VMQ (Vinyl Methyl Silicone), often simply called silicone in the SCUBA industry.

VMQ was chosen by many underwater housing manufacturers for two reasons. First, it is highly resistant to weathering and ozone, something NBR (Nitrile) is notoriously poor at. Second, it has an excellent compression set, meaning it can withstand being compressed for prolonged periods without losing its shape. People often leave housings tightly closed during storage, which can last for months. An elastomer with a poor compression set, such as EU (Polyurethane), was a no-go. VMQ ticks both of these boxes. In fact, it has one of the best compression sets of any elastomer used in the SCUBA industry (disregarding its other, less favorable characteristics...).

However, VMQ has one peculiarity that is highly relevant in the SCUBA industry, though it’s not exclusive to VMQ. Silicone grease is typically made up of silicone oil and thickening agents. Because the structure of silicone oil is very similar to the structure of the VMQ elastomer, it can diffuse into the elastomer, causing swelling. Simply put, the silicone O-ring absorbs some of the silicone oil from the grease and expands. But it doesn’t just get bigger, the swelling causes significant changes in the tensile modulus, lowering it. This makes the O-ring very prone to extrusion over time.

This swelling issue isn’t confined to VMQ O-rings. For example, EPDM performs exceptionally poorly with fuels and oils. I’ve seen cases where people used Vaseline as a substitute lubricant, causing EPDM to swell significantly and lose much of its tensile modulus. Similarly, FKM struggles in polar environments, such as acetone.

However, the SCUBA industry generally focuses on the lubrication properties of greases and pays little attention to chemical compatibility. The reason is that nearly all elastomers used in SCUBA tolerate silicone grease well, except for VMQ (silicone). This is why camera housing manufacturers sell their "special" grease. It’s simply a grease compatible with the specific elastomer they use.

In yoke style regulator connectors the captured o-ring if lubed will extrude, leak air and possible damage the 0-ring.

This is a common misconception. The yoke O-ring functions as a face seal, meaning it gets compressed between two surfaces, one of which has a groove cut into it. A face seal is highly dependent on an even force applied to the O-ring. Any eccentric forces will quickly cause leaks. A high tensile modulus is especially beneficial for this type of seal, as the O-ring isn’t fully captured, unlike, for example, the O-ring on a DIN barrel (even though that is also a face seal).

Incidentally, this is exactly why ScubaPro chose an EU (Polyether-urethane, often simply called Polyurethane in the SCUBA industry) O-ring for this application. EU has a very high tensile modulus and is exceptionally resistant to weathering and ozone. Its poor compression set is of no concern in this application.

Over lubricating leads to slippery o-rings on most of the extruded ones but any lube lowers the coefficient of friction.

It is a common misconception that lubrication lowers friction and therefore promotes extrusion. However, as shown in the pictures above, only gap clearance and the tensile modulus of the elastomer play a role in this process. When modeling the O-ring as a highly viscous fluid with high surface tension, it becomes clear that friction becomes largely irrelevant.

I concede that there is a small point to be made here regarding friction playing some role. One study I’ve seen on the topic was conducted in 2019. While the study concludes that friction plays a role, if you examine the details, the authors concede that friction is directly affected by gap clearance, which makes sense when you think about it.

Again my question: Why not put a correct [based on % oxygen] lube on tank valve threads to preclude the possibility of galling and for easy removal for VIPs/hydros?

Even Krytox and Christolube are contaminants. They are far more resistant to ignition than hydrocarbon greases, but crucially, they are not immune to it. For example, Krytox has an autoignition temperature of just over 427°C in 10.3bar of 100% oxygen, and once it burns, it releases a heat of combustion between 3768J/g and 4187J/g. These are incredibly impressive values, but again, they do not mean "doesn’t burn". The absence of grease is inherently safer than its presence. Any grease will burn if pushed far enough, even oxygen-compatible grease.

No need to lube base of valve or snorkel; galvanic corrosion requires metal to metal contact as with valve threads to tank threads.

As I mentioned earlier, this is incorrect. The key factors are the surface areas of the cathode and anode in contact with the electrolyte. Having only metal-to-metal contact with no electrolyte present would actually be an advantage, as no electrons could flow from the anode to the cathode. Galvanic corrosion depends on the presence of free ions in an electrolyte, such as water. In a real SCUBA tank, things like carbonic acid would will act as even better electrolytes than plain water. Saltwater works much better as an electrolyte than freshwater, due to the many more free ions contained in it.
Be that as it may, galvanic corrosion does not take place without an electrolyte.

As for lube "attracting" dirt/grit and contaminants; when used in a clean environment I have never found this to be an issue.

I absolutely agree with you here, but this is an idealized scenario. The SCUBA industry is unlike most other industries, which have tight control over their processes. Our equipment spans from highly organized shops in the Western world to poor fishermen in developing countries and everything in between. Even in wealthier Western countries, more shops pump wet air than I would like to see.

 

[Tanks A Lot]

Part 3:​

I have found that cleaning off Dow 111 from threads of valve or tank easy.

I agree to disagree on this. I’ve found that thoroughly cleaning out old grease is a cumbersome task. While unlubricated threads can be easily cleaned with a spiral brush, lubricated threads require more attention. Short of using something like isopropyl alcohol and a brush, I haven’t found anything that genuinely cleans out old grease. A tissue or spiral brush alone certainly doesn’t cut it.

[...]the rather arbitrary limit of EAN40[...]

Even worse, some parts of the world and industries have adopted an "everything over 21.5% O2" approach. This was based on, in my view, a flawed study that shifted the goalposts considerably to make its point.

Lubricating the threads can have some advantages in ideal scenarios. However, the reality of the SCUBA industry and the potential adverse effects outweigh these benefits. There’s a reason why the recommendation to lubricate was removed from the ISO documents, and I presume it aligns closely with the reasons I outlined above.

Lubricating O-rings, on the other hand, is cut and dry (no pun intended!). A static O-ring needs lubrication for installation and for those final tiny movements to reach its seating position. I’m honestly not quite sure where the myth in the SCUBA industry that static O-rings shouldn’t be lubricated originates from. I’ve tried to track this down for quite a while without much success. However, looking at any other major industry, especially the elastomer industry itself, the answer is readily available and obvious: grease all O-rings, whether static or dynamic. Dynamic O-rings might require a bit more grease, but that’s a different story.

Extrusion boils down to the gap clearance and the tensile modulus of the elastomer.

With regards to the gap clearance:

• A higher gap clearance promotes extrusion.
• An uneven or eccentric gap clearance promotes extrusion.
• Sharp edges on the gland can cut into the material, promoting extrusion. For good reason, the square profiles you see on aluminum cylinders are not truly square but have a 5° taper cut into the groove. This prolongs O-ring life.
• Tangentially related to gap clearance is the use of O-rings that are too large, causing overfilling of the gland. However, I’ve seen studies suggesting this may not be as significant a factor as once thought, so I’m cautious about this point.

With regards to the tensile modulus:

• A low tensile modulus allows the O-ring to squeeze more easily through the gap clearance.
• Tensile modulus is directly correlated to the durometer, the harder the elastomer, the higher the tensile modulus.
• Temperature can lower the tensile modulus by altering the structure of the elastomer, though this is not a concern in SCUBA applications.
• Chemicals can change the structure of the elastomer, so proper lubrication selection is key.

If you’re interested in the topic, I’d suggest Parker’s O-Ring Handbook, which is an excellent read and has been an industry benchmark for decades. Other sources, such as those from Eriks or EPM Inc., are no less informative.

 

[Wallowa]

T.A.L......Appreciate not just the dialogue and information but the civility in which you offer that information.

I am a great believer in 'scientific method' but also equally believe in experiential truthing. Like you say the SCUBA industry used lube as a lubricant. Lubricants reduce friction and can reduce metal to metal contact which as you pointed out in the such contact in the presence of an electrolyte can lead to the migration of one metal into the other [anode/cathode] which causes galling between threaded surfaces.

Electrolyte between the threads of the valve and tank must come from water moisture in the gas going into the tank or water entering the valve into the tank. Both of these events happen within SCUBA tanks; both are preventable but even "dry" air will contain some water vapor. So what are the options to lessen or prevent damage to the threads, any of the threads, by galling? 100% dry air all the time, not happening. Never empty a tank and allow moisture into it, this will happen. Put a lube on bottom threads of tank valve which when threaded into tank will move that lube up the valve threads and tank threads. This lube puts a barrier between dissimilar metals of valve and tank to lessen or prevent galling and to ease removal of the valve. As you point out lube also blocks entry of electrolyte between the threads.

As for making any torque settings inaccurate which can happen [some torque valves assume the use of a lube, some are only for dry settings], I would venture to say that 90+% of tank valves here are threaded in hand tight and then perhaps bumped an 1/8 of a turn with a rubber mallet. I have never seen, not that it does not happen, a torque wrench used to install a tank valve. In our currently increasingly litigious society perhaps torque wrenches will be mandated. Hope not.

Electrolyte migrating under the lube would have to occur on both surfaces and be sufficient to facilitate the transfer of current/galvanic exchange. Bare threads would not have anything between the two threads to inhibit this migration of electrolyte and transfer of metal. Entry of electrolyte and draining of electrolyte from between these threads is a mystery to me, but once in galling starts.

Again, must have metal to metal contact, so bottom flat surface of valve and metal of snorkel do not have metal to metal contact with another metal surface. Galling is not an oxidation process.

Jump to high pressure 100% oxygen use. Undoubtedly anything can combust given enough heat, oxygen and pressure; but CGA and others do approve the lubes you mentioned for use with 100% oxygen.

Correct that a properly seated o-ring of the correct size and material for the contact area should never extrude. The necessity of any lube on a "static" o-ring seems to be negated if the o-ring properties allow the correct deformation to seal between the surfaces. While dynamic o-ring use profits from reduction in friction due to presence of a lube. Lubrication does reduce friction. The o-rings between the tank valve and the tank neck that I have seen extrude were caused by lubing and the extrusion occurs on initial tightening.

Lubricating any surface does take finesse as too much of a good thing is bad. Over-lubing is most often the problem with o-rings that results in gas leaks and/or cut/pinch damage to the o-ring.

Enough from me....bottom line, back to experiential learning, is I have seen a lot of o-rings on reg yokes leak due to cuts and pinches when the were extruded and like wise I have never had galling on the thousands of tank valves or tank threads I have serviced over the years [25] while using Dow 111. Lucky? Perhaps. But just for me I will stick with observed results while using the correct lubing of threads between dissimilar metals. I am not an expert but only experienced.

Again; do value and appreciate the information you have presented. We can agree to disagree on some of that, but it has been a good dialogue for me. Thanks I have learned from the exchange.

Out Here.

 

[Tanks A Lot]

I likewise enjoy a civilized conversation!

Like I said before, lubricating can have certain advantages, but the real world disadvantages it introduces outweigh these for me. I know I said it before, but this is a situation if you are damned if you do and damned if you don't.

With regards to galvanic corrosion, I think a lot of the misunderstanding stems from the fact how you picture it.
Galvanic corrosion specifically does not involve metal to metal contact along the whole surface area, but rather just requires the two metals to provide a path for electrons to flow. This is always given, as it is all but impossible to isolate the valve and cylinder from each other in real world scenarios.

1. If we look at the picture above it starts with the water self ionizing:
H₂O → OH^- + H⁺

2. Now the iron on our anode oxidizes:
Fe → Fe²⁺ + 2e^-

3. Those two Fe²⁺ molecules now react with two OH^- molecules from the ionized water which completes the :
Fe²⁺ + OH^- → Fe(OH)₂

4. Going to the copper side cathode, virtually the same happens. This is suspiciously the same as step 2:
Cu → Cu²⁺ + 2e^-

5. Now comes the crucial difference. The Cu²⁺ ions get reduced (gain electrons) from the anode and the electrolyte. This is because the standard electrode potential of copper is higher than that of iron:
Cu²⁺ + 2e^- → Cu

What happened is in essence is that the cathode side continuously steals electrons from the anode side, no direct contact needed.

To complete the reaction, there would also be hydrogen gas forming, which I will omit here. I have chosen iron and copper because of the ease of the reactions, but the same holds true for other alloys. From the picture and the formulas it should become clear that the relative surface areas exposed to the electrolyte are of utmost importance! The higher the exposed surface areas, the faster the oxidization on the anode side as more iron will oxidize due to the larger surface area reacting with the electrolyte.

This is exactly why it would be so important to lubricate the base and/or dip tube of the valve. Like I said before, this is nearly universally misunderstood by technicians working on SCUBA gear. Most even demonize the plastic dip tubes when in reality they are a clever way to combat galvanic corrosion. I had this discussing with one engineer working on valves. He admitted that he doesn't know if some manufacturers do it to lower costs, or if they truly understood why a plastic dip tube makes sense.

Lubricating the threads to prevent galvanic corrosion is sound in as far as it reduces the surface areas exposed to the electrolyte. And here the dip tube and base are a universally overlooked piece of the valve exposed to the electrolyte.

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If I have given the impression that galling has anything to do with oxidization I apologize for my poor wording. On clean threads, the threshold for galling is significantly lowered by lubrication, there is no argument here. This is one of its main advantages.
But the moment that lubrication picks up any debris it is a different story. And from my experience, lubricants pick up debris like magnets and are notoriously hard to properly clean out of threads. Not many shop technicians I have observed go through the painstaking method of using a brush and isopropyl alcohol. And given this scenario, the grease will eventually, unintentionally, promote galling by accumulating lose debris.

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You may find the attached, admittedly dated, study interesting. It specifically mentions the dip tubes and the importance of reducing their surface areas. It also suggest to lubricate the threads liberally. I admit that I pick and choose a little here, but I have laid the reasons out for it earlier and still think they are sound. On a side-note, the way the study mentions ingestion of saltwater is hilarious to me, so I guess it is somewhat fair that I read all of it with suspicious eyes.

I think we are mostly on the same page, but you are more optimistic about things. You start your reasoning from ideal starting points, while I assume adverse scenarios. Maybe this has to do with the different regions we worked in.

I appreciate the dialogue, it is always interesting to read differing views coherently presented, thank you! This is the only way we can truly expand our horizon.

 

[Wallowa]

Very cool and thanks yet again.....I have that NOAA Sea Grant report and knew John....expected results for the abused cylinders ...conclusions did mention thread lube and included snorkel...good study.

I was incorrect in indicating that metal to metal contact was necessary for any galvanic current and corrosion.. only need the metals simultaneously in contact with an electrolyte or in contact with each other in the presence of an electrolyte ....such ionic transfer in batteries or the thread to thread corrosion I was fixated on the tank valve and tank threads.

Take care and appreciate the information and perspectives...had to laugh though, I am anything but an optimist ["but you are more optimistic about things"] and I am very much a "trust with verification" guy!

See you list "Germany"....Ask me how much I loved the Augustiner Keller beer garden in Munich.....no equivocating about that!