O-rings???

[Mr Carcharodon]

How long will spare o-rings last befoe replacing them.

If they are sealed from the air, and keep in a cool place I would not be too concerned about using a 5 year old o-ring. And for applications that are not safety critical 10 years would probably be OK. I know I have used o-rings at least that old. They will form a surface oxide layer (or at least Buna does), but that can be cleanded off. If the rubber is stored in a warm place, and exposed to air the lifetime will be less, maybe less than a year. I would stick to less than 4 years if the loss of that particular o-ring would put you in danger.

A.

 

[kevink]

70 vs 90 durometer may not make a huge diference for a tank valve to tank seal. The lower the durometer the squishier it will be. Lower durometer o-rings will seal better, but will also tend to have a shorter life (as they may not be abrasion tolerant). Silicone tank valve rings are nice since they rarely leak, but they are pricey, and have a shorter life. Middle of the road is Buna-N which is stock at 70 durometer. At the higher end Viton o-rings have great environmental and abrasion resistance, but they are harder and pricey again.

If you want more information about o-rings than you care to know, read the first 10 pages of Apple Rubber's catalog, along with the troubleshooting section in the back of the book. You can download the catalog, or request a hardcopy from them, if they are nice enough to send it.

Not only heat and moisture, but exposure to UV is a killer for o-rings. Be mindful of what you lubricate them with, not that I think anyone uses pertroleum based lubes anymore. Even when something says silicone lube, read the label to make sure it is not a suspension of anything else.

 

[Mr Carcharodon]

PSI sells tank O-rings on there site for tank necks. They are 90 durometer and McMaster seems to only sell 70. Which one is best for tanks the 70 or 90?

Harder rubbers are less prone to extrude from a groove. In the back of the Parker Seals catalog the have a chart that shows recommended pressures for different hardness rubbers. They do not recommend 70 durometer above 3000 psi. 90 durometer is OK for low clearance grooves up to 10,000 psi. But acceptable pressues depend on both the rubber hardness and the geometry of the groove. On the other hand softer rubbers will tend to seal better against surface imperfections.

I have used 70 durometer in a DIN connection at 3500 psi, so I suspect Parker is being a bit conservative. Still they are probably right for best reliability stick to 90 durometer for applications above 3000 psi.

I would use 70 durometer viton for any application <3000 psi since they work well in my experience, and the higher up front cost is offset my longer periods between replacements. But Buna Nitrile is more readily available.

A.

 

[contengo]

I like using polyurethane. It seems 90 is better than 70 under pressure. I have bought from Mcmaster-Carr before. Until I saw this. http://www.oringsusa.com/html/oem_resellers.html If you look carefully, you can see Mcmaster-carr logo there. They sell every kind of oring under the sun, but it seems you have to buy a bag of 1,000 pieces. That's a lot of diving.

 

[BuoyantC]

Has anyone out there compiled a cross reference list of commonly used o-rings to their as-586b numbers and corresponding hardness? Just something I'd toss in my reference file if I had it.

Dennis

 

[Tiny Bubbles]

Has anyone out there compiled a cross reference list of commonly used o-rings to their as-586b numbers and corresponding hardness? Just something I'd toss in my reference file if I had it.

Dennis

I've been compiling a list of sizes for a while...

http://69.47.246.17/diving/o-rings.xls (click my avatar and 'surf' to it if this link ever stops working)

There's also some very old threads on this board on the subject.

I've found air-oil.com to be a good source for buying o-rings.

-Tiny-B.

 

[1_T_Submariner]

I use a lot of O-rings in Hyd apps that require Viton. We buy them at Zatkoff.

http://www.zatkoff.com/