I would like to make this an easy task. Is there a perticular o-ring material that is best for pcp guns. Im thinking about making a stash of all from my gun o-rings and would like to keep is simple.
N/A O-rings
- Thread starter imtrigerhapy
- Start date
I made a stash. Bought captain oring kits where I could, they send some high end compositions where needed. I have kits for my really good shooters, some have multiple kits. It's a pain to store and I should vacuum pack them in a glass jar for longevity.
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I just buy the big kits of different sizes. Then when I need an oring I play musical boxes to find the one that fits. Actually I usually stick the calipers on them and grab the right size.
I also buy the kits with same sizes different material.
I go through a lot of orings playing around with my guns and my latest stupid idea.
The problem with my method is that there are a few sizes that are used a lot so you have a huge oring set missing two orings and one of the missing is why you have that set.
I also buy the kits with same sizes different material.
I go through a lot of orings playing around with my guns and my latest stupid idea.
The problem with my method is that there are a few sizes that are used a lot so you have a huge oring set missing two orings and one of the missing is why you have that set.
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The simple answer: Buna-N in 70 durometer
The longer answer...
Static and dynamic O-rings carry different considerations and tradeoffs.
Static O-rings
For static O-rings (air tube, valve, etc.), Buna-N is the de facto material of choice. Long life, good resistance to compression set and tearing, and low permeability. Inexpensive and widely available in both standard (AS568) and metric sizes, and in both 70 and 90 durometer.
FKM (Viton) in my experience also works fine for static seals, with the caveat that it swells. This behavior is a nuisance more so than a problem, meaning if you need to disassemble, you will have to either replace it or wait for it to outgas and return to its original size before you can reassemble. Viton also has improved high temperature resistance, making it a good choice for O-rings on the high-pressure end of a regulator.
In terms of durometer (hardness), 70 is usually good for up to 3000psi and somewhat beyond. Step up to 90 durometer for higher pressures to reduce the risk of extrusion failure. Just depends on part tolerances. If the gap between the mating surfaces is abnormally large and the elastomer is soft (low durometer), the material will extrude into the gap like playdough and damage the O-ring and begin leaking. If it happens, you’ll know it when you see it because the O-ring will develop little wispy wings.
Dynamic O-rings
For dynamic O-rings (e.g. bolt or breech O-ring), go with either polyurethane or Buna-N. On paper, polyurethane is the better of the two in terms of abrasion resistance but in practice I can’t say I notice a difference. And bear in mind polyurethane has the lowest shelf life of all the common elastomers (5-10 years) so you probably don’t want to load up with a bunch of spares on the shelf just to have them age out before you can use them.
Higher durometer improves abrasion resistance as well so go with 90 durometer if you can. You’ll have to use some judgment because a hard O-ring is simultaneously at greater risk of getting a bite taken out if it sees any sharp edges during installation or in daily use.
Lubrication
For static O-rings, a viscous silicone grease like automotive dielectric grease or diver’s grease is helpful as an assembly aid. It also reduces gas permeability which in turn is beneficial to the longevity of most materials.
For dynamic O-rings, a less viscous silicone oil is good. Something like 20 – 30W silicone oil sold as RC shock oil.
The longer answer...
Static and dynamic O-rings carry different considerations and tradeoffs.
Static O-rings
For static O-rings (air tube, valve, etc.), Buna-N is the de facto material of choice. Long life, good resistance to compression set and tearing, and low permeability. Inexpensive and widely available in both standard (AS568) and metric sizes, and in both 70 and 90 durometer.
FKM (Viton) in my experience also works fine for static seals, with the caveat that it swells. This behavior is a nuisance more so than a problem, meaning if you need to disassemble, you will have to either replace it or wait for it to outgas and return to its original size before you can reassemble. Viton also has improved high temperature resistance, making it a good choice for O-rings on the high-pressure end of a regulator.
In terms of durometer (hardness), 70 is usually good for up to 3000psi and somewhat beyond. Step up to 90 durometer for higher pressures to reduce the risk of extrusion failure. Just depends on part tolerances. If the gap between the mating surfaces is abnormally large and the elastomer is soft (low durometer), the material will extrude into the gap like playdough and damage the O-ring and begin leaking. If it happens, you’ll know it when you see it because the O-ring will develop little wispy wings.
Dynamic O-rings
For dynamic O-rings (e.g. bolt or breech O-ring), go with either polyurethane or Buna-N. On paper, polyurethane is the better of the two in terms of abrasion resistance but in practice I can’t say I notice a difference. And bear in mind polyurethane has the lowest shelf life of all the common elastomers (5-10 years) so you probably don’t want to load up with a bunch of spares on the shelf just to have them age out before you can use them.
Higher durometer improves abrasion resistance as well so go with 90 durometer if you can. You’ll have to use some judgment because a hard O-ring is simultaneously at greater risk of getting a bite taken out if it sees any sharp edges during installation or in daily use.
Lubrication
For static O-rings, a viscous silicone grease like automotive dielectric grease or diver’s grease is helpful as an assembly aid. It also reduces gas permeability which in turn is beneficial to the longevity of most materials.
For dynamic O-rings, a less viscous silicone oil is good. Something like 20 – 30W silicone oil sold as RC shock oil.
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Wow thays alot of great info thank you very much i appreciate the time it took you for that
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What gun are you working on? Most manufacturers will release a schematic and if your lucky a parts listing of sizing and hardness specifications for the O-rings. I have put together several kits of the needed O-rings to rebuild my air rifles. Yeah, it is a pain getting the kits together and at times you will be lucky enough to find a kit from Captain O-ring, vendors or the manufacturer.
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Im sure ive seen kits for both but it seems if i do the looking i could assembe multiple kits for about the same price and have several of the spares for common ones
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