To lube or not to lube O-rings?

[johndiver999]

My favorite oring discussion.
It's true static oring don't need lube, trouble is there is a big misunderstanding of the definition of what a static oring is.
Most believe that once it's in place and does not move (or the parts around it) while in place it's static, the rub here, if you forgive the pun, is to meet the definition of static, the oring can never move against it's mating surfaces. During installation , hose orings move in a spiral rotation while being installed, at that time they are in fact dynamic and need lube. You have to dig deep in the Parker manual but this is discussed (or at least it was years ago). Many will argue that they have not lubed hose orings for years and it worked. No doubt this is true but odds are there was still some remaining lube, it only takes a little, or they got lucky.
Then there is the movement the oring does as it transitions from it's non-sealed state to it's sealed state.. This is discussed in the thread referenced above, you will see the how the oring moves in it's groove while being pressurized, this movement also needs to have some lubricant to prevent binding.
The only true dynamic oring in scuba that I can think of is the tank to valve interface. The oring is pressed into a groove then pressed straight on to the flat surface in the tank., or vise versa depending if it's DIN or yoke.

I don't understand the bolded comment. Why isn't that o-ring subject to torsional forces as it is screwed down? Why is it materially different than a port plug on a first stage? I always lube that one. I think it may help with corrosion as well.

 

[GJC]

I don't understand the bolded comment. Why isn't that o-ring subject to torsional forces as it is screwed down? Why is it materially different than a port plug on a first stage? I always lube that one. I think it may help with corrosion as well.

While being compressed, there is no rotation of the mating surfaces as the yoke screw is tightened.

 

[happy-diver]

but the grease helps the oring jump out more

 

[johndiver999]

While being compressed, there is no rotation of the mating surfaces as the yoke screw is tightened.

Read the bolded comment again. Perhaps it is a typo

 

[broncobowsher]

Here is one for you. Kubi dry glove. Once on there is no pressure delta across the O-ring nor does it rotate. The friction of the O-ring is what holds the glove on.

Do you lube?

I do, slightly. Learned to put a smear of zipper wax on. Buff into the rubber so it has a little shine to it. Test fit. Too tight, need more lube. Too loose, buff more lube off. You can fine tune the friction fit with the application of lube.

I have heard stories about the Kubi needing 2 spoons to pry them off. That is just neglect of maintenance. Get your little lube in place and they will be fine. I have had them get a little stiff, that is just my cue to lube them. Not to continue to ignore and complain about how hard they are to get off due to the lack of maintenance.

 

[Oldbear]

Read the service manual...not all o-rings should be lubricated.

 

[OTF]

Read the service manual...not all o-rings should be lubricated.

When SHOULDN'T an o-ring be lubricated? Would be interested in examples.

 

[Akimbo]

When SHOULDN'T an o-ring be lubricated? Would be interested in examples.

O-rings used to add resistance in a mechanism instead of sealing would qualify for never lubricating. Also, certain applications when leakage is non-critical and the environment is contaminated with fine abrasive particles that would collect on the lubricant meet the "shouldn't" designation. Low pressure air quick disconnect fittings in industrial some plants for example.

Consider a wood shop where you frequently switch between an air nozzle and pneumatic nailers for example. Wood particles would abrade the O-ring faster than using the dry O-ring and leakage is of no real consequence. Of course most industrial LP air systems include a lubricator to add an oil mist to the air stream to lubricate pneumatic tools.

 

[davehicks]

When SHOULDN'T an o-ring be lubricated? Would be interested in examples.

Back of a camera housing.

These are compression orings that are completely static. They are exposed to sand, grit, hair, and lint constantly. Lubing them accomplishes two things. 1) They pick up more grit. 2) Some people lube these long pliable orings like a Stretch Armstong toys to the point they don't fit in the grove properly resulting in a flood of the housing.

 

[Akimbo]

Back of a camera housing.

These are compression orings that are completely static. They are exposed to sand, grit, hair, and lint constantly. Lubing them accomplishes two things. 1) They pick up more grit. 2) Some people lube these long pliable orings like a Stretch Armstong toys to the point they don't fit in the grove properly resulting in a flood of the housing.

Camera housing manufacturers disagree. Properly lubricating these O-rings includes a very light coating and the process of lubricating it includes inspecting and cleaning any debris that accumulates. Your point is well taken in that debris can contaminate in the sealing surfaces. This is independent of whether the the O-ring is lubricated or not. Lightly lubricating O-rings not only allows the O-ring to move to the pressure-seating position in the groove, it facilitates installing it in irregular grooves. It is much harder for non-lubricated O-rings that stretch during installation to evenly equalize the stretch in the groove.

All O-rings move in the groove unless the pressure is very low, like less than half an atmosphere. See the illustrations in O-rings for Divers.

I avoided the term static because it has a particular meaning in O-ring engineering. Static O-rings mean that the seating surfaces are intended not to move relative to each other in operation. It does NOT mean that the O-ring does not move in the groove.