Use of silicone grease on reg port screws?

[Luis H]

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.

Hi Matt

Technically speaking, you are absolutely correct on the most accepted definition of a dynamic O-ring versus static O-ring. The issue is (like most things in real life) is that there is a large grey area... some could say it is black and white, but would not totally agree with that.

I will try to explain.
The O-rings that we think of dynamic in a Scuba regulator are really almost static for most of their life. At 10 breath per minute (the total normal range could be from 6 bpm to maybe 14 bpm working hard) and a normal operating time of a few hours a week (heck, even a theoretical commercial diver with a 40 hour per week) you can see that there are not very many cycles on a regulator.

The wear you see on all regulator O-ring is not really normally wear (there are always some exceptions if the surface is rough, no lubrication at all, etc.), in reality it is just compression set from spending most of its life in a compressed state.

So yes dynamic O-rings are definitely dynamic, since they do slide under service, but not by much, since they don't really slide much.

The point was that some of the static O-ring also has to slide some during installation... and if you see how I sometimes reconfigure my LP hoses in a weekly basis, you could almost say that some of my static O-ring get more sliding cycles than some dynamic O-rings.

One big distinction should also be face seal, versus gland seal, versus crushed corner seal.
Examples:
Face seal:

• Tank to regulator O-ring, DIN or yoke

Gland seal:

• Piston O-rings, dynamic
• Second stage hose swivel O-ring, dynamic
• Modern double tank manifold O-ring, static

Corner crushed O-ring:

• Tank neck O-ring, mostly static
• First stage hose O-ring, mostly static again.
• Some camera housings, for the most part static.

A big difference between the O-ring geometries specified, is that the gland seals require a well design and manufactured gap for assembly and some times to allow operating motion.

Most dynamic O-rings are in a gland seal configuration, but I have seen some very unique face seals that do rotate and even translate.

 

[Daiika]

Luis and Herman thank you for the fine detailed information. But for an average diver it would be hard to remember which is a face seal gland seal or crush seal. Is it safe to say to lightly lube all o-rings except the tank to regulator o-ring?

 

[halocline]

Luis and Herman thank you for the fine detailed information. But for an average diver it would be hard to remember which is a face seal gland seal or crush seal. Is it safe to say to lightly lube all o-rings except the tank to regulator o-ring?

I guess that depends on whether the average diver is taking apart his regulator and removing his tank valve. If not, then what o-rings are you referring to? No problem lubing the regulator hose and/or port plug o-rings if you have occasion to remove 2nd stages, LP hose, or SPG from the 1st stage. I can't think of any others unless you get into servicing.