O Ring Duro Enlightenment

[kissdom]

Hello All,

I have a question regarding O-ring Duro. This is one of the O-ring chart I found online, however at some other charts, series 10,11,13,14 used duro 90 for the V series.

I know its the difference between hardness of the O-ring, but how should I decide on which Duro O-rings to use?



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[TD="class: TextObject, width: 187, colspan: 3"]-003 HP Hose/ SPG Swivel
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[TD="class: TextObject, width: 187, colspan: 3"]-010 LP Hose / 2nd Stage
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[TD="class: TextObject, width: 187, colspan: 3"]-011 Standard 3/8" LP Port
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[TD="class: TextObject, width: 210, colspan: 8"]-012 7/16" HP Port/ Hose Manifold
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[TD="class: TextObject, width: 187, colspan: 3"]-013 1/2" LP Large Port
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[TD="class: TextObject, width: 206, colspan: 6"]-014 Std Yoke Regulator/ K-valve
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[TD="class: TextObject, width: 187, colspan: 3"]-111 Small DIN Regulator/Valve
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[TD="class: TextObject, width: 208, colspan: 7"]-112 Standard DIN Regulator Valve
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[TD="class: TextObject, width: 187, colspan: 3"]-116 1/2" Tank Neck (small)
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[kwinter]

In general I use 70 for any low pressure application and 90 for high pressure. So that means I have some sizes in both duro.

 

[herman]

The harder the rubber, the more pressure differential it can stand and conversely, the lower the differential pressure, softer rubbers work better. So, use 70-75 in LP/IP applications and 85-90 in HP ones. The Nitrile vs Viton is somewhat BS and IMO the cost of viton is not usually worth it. Viton is more resistant to oxygen and will tolerate exposure to it longer than nitrile but it takes a good bit of time before the difference starts to show up, rebuilds are usually done way before it would start to make a difference. Now IF you are using high O2 mixes then viton is a good idea but for the normal 30-36 % O2 I don't see the need.

 

[kwinter]

I take a slightly different view than Herman. The things cost only pennies when bought in bulk. I don't see any reason to have a mix of Buna and Viton. I only buy Viton so they are good for any application, whether needed or not. That way I don't have to think about the application or keep them separate. The only downside of Viton is the cost. For a size 010, they are 6 cents each instead of 3 cents. My peace of mind is worth it.

 

[redacted]

I take a slightly different view than Herman. The things cost only pennies when bought in bulk. I don't see any reason to have a mix of Buna and Viton. I only buy Viton so they are good for any application, whether needed or not. That way I don't have to think about the application or keep them separate. The only downside of Viton is the cost. For a size 010, they are 6 cents each instead of 3 cents. My peace of mind is worth it.

For the life of me, I'm just not sure why o-ring material is a "peace of mind" consideration in a scuba regulator. Maybe in a space craft....

Buna is really not a bad material for scuba application, even with recreational nitrox (except in a valve used for PP blending). But there are characteristics other than cost that are worth considering. A big one is availability; and buna is often the most readily available material. It's not that I see anything wrong with viton but the cost differential can be much more than a factor of 2 and the added benefits are just not that great. EPDM (may take some shopping to find) is another good alternative with similar characteristic to viton and cost closer to buna. Urethane (also hard to find) tends to be more expensive than viton but it has more favorable dynamic characteristics and resistance to extrusion. When a 10V90 (really hard to find EPDM in duro 90) HP piston o-ring gives me problems, I usually resort to urethane.

I also use duro 70/75 o-rings in many HP applications unless I am having an extrusion problem. HP port plugs and hose connections for example. They are easier to install (especially that 003) and rarely a problem. A port plug extrusion problem gets a different port plug rather than a different o-ring.

If the potential of an o-ring failure affected my peace of mind, I would not be scuba diving.

 

[kwinter]

Not sure where you are that you say they are hard to find. Oringsusa.com, theoringstore.com, and others make it very easy to get Buna, Viton, urethane or EPDM cheap and easy.


iPhone. iTypo. iApologize.

 

[redacted]

Not sure where you are that you say they are hard to find. Oringsusa.com, theoringstore.com, and others make it very easy to get Buna, Viton, urethane or EPDM cheap and easy.


iPhone. iTypo. iApologize.

I did not see any EPDM 90 at either of those locations.

 

[kissdom]

thank everyone for sharing!!

what happens if we use 90 duro hardness o ring on LP applications?

The harder the rubber, the more pressure differential it can stand and conversely, the lower the differential pressure, softer rubbers work better. So, use 70-75 in LP/IP applications and 85-90 in HP ones. The Nitrile vs Viton is somewhat BS and IMO the cost of viton is not usually worth it. Viton is more resistant to oxygen and will tolerate exposure to it longer than nitrile but it takes a good bit of time before the difference starts to show up, rebuilds are usually done way before it would start to make a difference. Now IF you are using high O2 mixes then viton is a good idea but for the normal 30-36 % O2 I don't see the need.

 

[kwinter]

Harder means less flexible, which means less likely to give a good seal without the extra pressure.


iPhone. iTypo. iApologize.

 

[herman]

That is about it. In contrast, using a 70 in place of a 90 might allow it to extrude out and eventually blow out. If it does or not depends on a lot of factors, esp the pressure differential and the tolerences of the metal parts around the seal.
If you have an interest in learning more than you ever wanted to know about orings, download the Parker Oring manual.