Use of silicone grease on reg port screws?

[Couv]

To lube or not to lube, that is the question. Some engineers and some manufactures deem it unnecessary to lubricate static o-rings because in their view it may actually lead to o-ring extrusion. Others instruct that static and dynamic o-rings should be lubricated in order to get a better seal. I just checked the SP MK 20/25 manual and it clearly states to lube the port plug o-rings. The AL Legend manual states the same.

I lube the o-ring and threads because if there is a leak, it will be minor and can easily be detected and corrected. At any rate, not lubricating regulator static o-rings is no big deal either for the same reason.

Couv

 

[herman]

Couple of thoughts here.
Thinking about it for a minute I can think of no truly static Orings in any scuba reg I can think of. The closest thing I can come up with is the diaphragm in a second stage that uses clamps to hold the 2 halves together. Not exactly an Oring but a truly static seal. Granted there are plenty of Orings that are static while in service, i.e. the mating surfaces don't move during operation - hose Orings for example- however every one that I can think of are in fact dynamic during installation. To be truly static the 2 mating surfaces have to be pressed together with no motion, other than compression, between the Oring and both mating surfaces- 2 pipe flanges that are bolted together with an Oring in between would be an example of a true static installation. The Orings in a reg that are static in service still have to be installed in a dynamic fashion...the oring slides past a mating surface on the reg body until it reaches it final position and therefore should be lubed. I lightly lube them all.

On camera housing Orings, some are static (Ikelites) and some are dynamic and in the case of my OLY PT-15 it has one of each. I lube them both lightly. The dynamic one because it needs lubrication and the static one because it installs easier with a little lube.......guess it is in fact dynamic during installation.

 

[keyshunter]

Herman,
How about the o-ring in the face of the din connector as a candidate for being truly static. Lubing this one causes it to fall out even more easily than normal.

 

[herman]

I don't use DIN and never paid any attention to them so I can't say but now that you bring it up, the o-ring in a yoke type tank valve is a good example of a static seal. Next time I get a chance I will look just for my own curiosity.

 

[Luis H]

Herman

That is a very good post and a good description of the difference between static and dynamic O-rings.

The yoke and DIN fitting both seal with the same type of static O-rings, also known as face seals. As a matter of fact old yoke valves use the exact same O-ring as a DIN.

Most camera housing that I am familiar with (Ikelite, etc), do not use a truly face seal, they are actually more like a gland seal. An example of true face seal is as you mentioned the pipe flanges. As far as I recall in most housings the sealing surface does slide a bit past the O-ring.



Added:
The idea of trying to reduce the chance of extruding an O-ring by having more friction (with no lubrication) is a poor and very unreliable concept. An O-ring extrusion is avoided by properly designed and manufacturing mating surfaces with appropriately designed small gaps. The small or non-existing gap is what will reliably contain the O-ring in its proper sealing place/ groove.

In Scuba gear, must of the O-ring that become static in service (such as the tank neck O-ring or the first stage hose O-rings), if they are properly installed and the parts are mating correctly, should have basically no gap for the O-ring to extrude. There should be some metal to metal contact if it is properly seated.

The mating parts that are sealed with dynamic O-rings will have a gap to allow the relative motion of the parts. The gap is carefully design for the application and working pressure to reduce the chance of an O-ring extrusion.

 

[Couv]

Luis and Herman,

Thank you, I have never hear it explained that way. I always considered "static or dynamic" as it related to an installed seal in use and pressurized. That brings to mind another thread http://www.scubaboard.com/forums/tanks-valves-bands/272569-lubricating-new-tank-valves.html where we discussed tank neck o-rings and lubrication. So as not to hijack this thread, could I get your input there?

Thank you,

Couv

 

[redacted]

Luis and Herman,

Thank you, I have never hear it explained that way. I always considered "static or dynamic" as it related to an installed seal in use and pressurized. That brings to mind another thread http://www.scubaboard.com/forums/tanks-valves-bands/272569-lubricating-new-tank-valves.html where we discussed tank neck o-rings and lubrication. So as not to hijack this thread, could I get your input there?

Thank you,

Couv

I lubricate port plug/ hose and tank neck o-rings, even if it is just some O2 compatible spit, so the threading action slides over the o-ring and will not bind. Only tank valve o-ring, din and yoke, stay dry as they are truly static and lube will just attract and attach dirt.

 

[halocline]

I would not confuse the difference between static and dynamic o-rings by bringing installation into the conversation. There's a fundamental difference between the way static and dynamic o-rings function in use. All o-rings and seals must be installed, and all of them must be moved, stretched, slid, compressed, or otherwise manipulated during installation.

The significant, practical difference between the two as it relates to scuba is that dynamic o-rings will be exposed to mechanical action that can cause wear while in use, and static ones will not. If you want to lubricate static o-rings (I do) to protect them during installation, fine, but that does not make them dynamic.

Another possibly (I don't know but I'm taking a guess) useful distinction between o-ring applications in scuba has to do with the pressure gradient that the o-ring is subjected to.

 

[knotical]

Luis and Herman,

Thank you, I have never hear it explained that way. I always considered "static or dynamic" as it related to an installed seal in use and pressurized. That brings to mind another thread http://www.scubaboard.com/forums/tanks-valves-bands/272569-lubricating-new-tank-valves.html where we discussed tank neck o-rings and lubrication. So as not to hijack this thread, could I get your input there?

Thank you,

Couv

Couv,
The thread was hijacked early on. The OP asked about lubricating threads, but most of us responded about o-rings. Responses about lubricating threads would not be hijacking, but would be quite appropriate in this, ah, thread.
k

 

[Couv]

Hi Matt,

I agree that to us mortals it is best not to confuse terms like static and dynamic when most of us have a simple and basic understanding of what they mean. However, in the engineering and manufacturing world there might be a reason not to apply the same terms as we understand them. Back in December '08 there was an interesting thread that explained the difference between "gauge pressure" and "sealed pressure". Again, it really has no effect on how I'll check my IP, but as it applied to the crux of that thread, knowing the difference could prevent one from making an error in the test being discussed. Similarly, when one hears a statement like "do not lubricate static o-rings" which may have originated from the design engineer who used the term in the way Herman and Luis explained. Most of us DIY guys don't simply blindly follow that sort of advice and lube "static" o-rings anyway. But, what about the every day user or even the dive shop technician? He sees a statement like that from an "authority" and to him it becomes gospel.

(figure eight) Knotical,

He, he, thanks for the dispensation.

Now if one of those sharpies can explain why most manufactures (not all) suggest NOT to lubricate the tank neck o-ring (valve to neck interface). "Lube only the bottom threads of the valve, not the o-ring" was the way I was taught as a shop monkey-and still blindly follow. Additionally, in the thread that I linked to earlier that seem to be the general consensus. But this discussion makes me question why.

Couv....always learning and forgetting.