The truth about gasket grease

[jseyfert3]

Right, my mistake. However, does the presence or absence of fumed silica make any difference here? We are just lubricating O-rings. We are not even greasing moving parts to reduce traction; we only keep the water out. I used the plumbing silicone with 2 housings, never had any problems.

I have no idea, except I imagine that a straight oil wouldn't be as good as a grease.

 

[tarponchik]

I have no idea, except I imagine that a straight oil wouldn't be as good as a grease.

Because rubber can swell from "straight oil". But not from silicone. Same reason why plumbers use it.

 

[JamesBon92007]

Actually I don't know the truth, I am seeking it.

I have a Recsea camera housing and Sea & Sea strobes. Each of these companies sells tiny tubes of silicon (I guess it is silicon) gasket sealant (grease) at outrageous prices. A salesman told me regarding the Recsea housing if you used another type of grease, the gasket would expand and be ruined, so I have dutifully used the official grease.

I looked at the Recsea manual and it says to use a silicon grease, no specific brand, with one caveat, don't use a spray grease. I don't think there is anything really wrong with the spray grease except that it would be messy and get grease where you don't want it.

Is it true that I must use each company's grease, or can I just go to a local auto parts store and buy a tube of silicon grease and use it on all of my gaskets?

I have been using food quality silicone grease on O-Rings and gaskets for decades without a problem. Currently I'm using Trident Pure Silicon Grease with satisfactory results. I would be very, very cautious about silicone sprays as some of them are not compatible with plastics.

If you were to use a petroleum-based grease then I can believe that some gaskets/O-Rings might expand.

 

[bvanant]

From Wikipedia:


Basically exactly what he said it was, when he said:

(except he said PDMS "grease" when it appears PDMS is an oil)

PDMS is polydimethyl siloxane. It can have a wide variety of physical properties depending on its molecular weight and its polydispersity (the distribution of molecular weights) . It can be a non-viscous oil or a rubbery solid depending. When I said grease I should have said oil, most folks (I think) believe a grease is a semi-solid lubricant. In any case, avoid the Home Depot stuff and get some of the Tribo/Christo/Krytox lubes and lets go diving.
Bill

 

[tarponchik]

PDMS is polydimethyl siloxane. It can have a wide variety of physical properties depending on its molecular weight and its polydispersity (the distribution of molecular weights) . It can be a non-viscous oil or a rubbery solid depending. When I said grease I should have said oil, most folks (I think) believe a grease is a semi-solid lubricant. In any case, avoid the Home Depot stuff and get some of the Tribo/Christo/Krytox lubes and lets go diving.
Bill

Those two greases originate from the same big tank somewhere in Dow or DuPont, most likely. Some is loaded into fancy little tubes and is sold to Canon, some goes to Home Depot in not-so-fancy jars, and both make some profit. Since no high vacuum ever gets nearby, everyone is happy.

 

[bvanant]

Unless your o-ring swells and you get a leak, then you probably are not happy. You are right that there are only a few suppliers for PDMS, at least at the less commodity levels. I would guess that most PDMS nowadays comes from China.

Bill

 

[tarponchik]

Unless your o-ring swells and you get a leak, then you probably are not happy. You are right that there are only a few suppliers for PDMS, at least at the less commodity levels. I would guess that most PDMS nowadays comes from China.

Bill

So far so good. I won't be surprised if they still make silicone here, then send it in bulk to China for vialing.

 

[Rred]

Silicon: That's the stuff of sand and grit, it chews up O-rings.
Silicone, with an "e". That's the stuff to use when rubber is not good enough. And, the lubricant to use with rubbers, because all rubbers (and a lot of plastics including lexan and plexi) are actually rotted or crazed by petrochemicals.

The details do count with this stuff. But only within limits.

Bear in mind that the FTC took the US auto industry to court in the 60's, and said you can't force people to use your brand of motor oil, you have to publish specifications and they can use anything that meets those specs and still have their warranty. If any company tells you to use "our lube only" and won't say what the specs are...call the FTC. If Papa gets bored, Papa may spank.(G)

About Krytox being PTFE/Teflon filled? I'd be surprised. Teflon is applied (liquid cured to solid) at a temperatire of 400-something Fahrenheit. Krytox is inert to over 700F, at which point Teflon would be toast.

We grease O-rings so they can slither around and not chafe or stick in their channels. And to keep corrosive oxygen and other chemicals off them. (Chlorinated water, etc.) And also, we grease them so the sharp little bits of siliCON can get stuck in the siliconE grease and cut the O-rings apart.(G)

 

[bvanant]

This is from DuPont
All standard grades of grease are thickened with polytetrafluuoroethylene (PTFE/Teflon), whose formula is (CF2-CF2)n. This special high efficiency thickener has a melting point of 325 °C (617 °F) and has low molecular weight and sub-micron (0.2 m) particle size for higher performance in bearings.
The Krytox you buy for scuba are indeed thickened with Teflon particles.

As for PDMS manufacturing it seems that today (2017) about 62% of all silicones are made in China although some of that is with US and European partners (Dow and Wacker)
Bill (who thinks we have exhausted this and should go diving)

 

[Rred]

I don't doubt you, BIll. Does make me curious what "standard grades" and "Krytox for SCUBA" mean, in the overall context of Krytox. I'm not sure which one I've used for gas pistons dealing with high temperature combustion gasses, but there must be differences. PTFE wouldn't survive in that use. Of course I may just be spoiled, Krytox used to come in "oil" and "grease" without all the newfangled variations.(G)

Its the stuff (any stuff) that only says "Shenzhen Best Export Quality" made by "Two Guys in Fine Basement" that I refuse to use.