$8.39 for ONE O ring!? (O ring questions) [MOSTLY SOLVED]

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Bernie7

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Oct 19, 2022
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Hello AGN! I’ve become much more interested in the engineering and maintenance of Airguns. I have some questions about o rings and hopefully I can tap into the wealth of knowledge here.

(Skip to tldr near bottom if you’re in a hurry)

The context is I was taking apart my PCP and looked up O rings and a kit for my rifle which brought up this criminal operation
https://www.ebay.com/itm/144686987987

And then a more reasonably priced listing (given they’ve already figured out the full set for you) seen here https://www.ebay.com/itm/275171603689

However, further Googling brings up options like this 250 Piece BN70 O-Ring Assortment we’re now down to $0.10/piece.

My questions are:
(I searched some previous threads and tried to fill in some answers myself, hopefully maybe get some more specifics)

  • Where do people source O rings?
    • The O Ring Store
    • O rings and More
    • …?
  • Are Nitrile Butadiene appropriate, or should I be looking for a different material
    • Fluoroelastomer - seems to have “better aging properties” (maybe ideal for air tank seal?)
    • Neoprene - “outstanding physical toughness” (or this one ideal for air tank seal?)
    • Polyurethane- “popular choice in wear applications where abrasives, high pressure, and movement are present” (specifically mention QD fittings for this one, and Airguns, likely the winner at least for breech seals)
  • Are the ones in the 250 count box likely to work or do Airguns use odd sizes separate from other industries?
    • Too many different sizes exist to have any good chance of fitting.
    • Use the sources listed above and a caliper to figure this out
  • Based on the answer above have we found certain manufacturers (Evanix) use specific sizes of O rings across models? Does anyone have schematics/blueprints? Where is this information compiled?
    • ?

TLDR- (EDIT, backfilled with info in replies)​

  • What materials should the o rings be, and for which uses?
    • For static below 3k psi use Buna-N in 70 durometer
    • For static above 3k psi (maybe) use Buna-N in 90 durometer
    • For bolt & breech seals, valve stems, and QD fittings use polyurethane.
    • Non pressurized & static areas can be poly or Buna-N
    • NOTE- dynamic seals should use silicone OIL (30 weight, search for silicone shock oil to not get ripped off, it’s the same active material but marketed to RC car hobby), static should use GREASE. Light application is preferred. Alternatively poly o rings can use PFPE/PTFE lubricant such as Krytox GPL-205.
  • Where do people source o rings
    • The O Ring Store
    • O rings and More
    • Mcmaster-Carr
    • Captain O Rings (their naming convention seems to be atypical so buyers should pay attention when placing orders, they use IDxODxThickness)
  • Do we have schematics compiled for Evanix models/where to find?
  • The guy charging $8.39 (+$5 s&h) for 1 o ring is a c**t
Thank you for your time!

Hope you all have an amazing weekend and hope you enjoyed the quasi click bait title :)
 
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For 95% of uses in PCPs, Buna-N in 70 durometer is a great choice. For static O-rings in particular (O-ring stays in one place to hold pressure). When dealing with pressures above 3000psi, it may be necessary to step up to 90 durometer. Same can be true at lower pressures if the parts have loose tolerances (extrusion gap between parts is large).

For dynamic O-rings—those that are subject to abrasion—polyurethane is a better choice. For the most part we are talking about bolt or breech O-rings. Granted, Buna-N will also last a long time in the vast majority of cases so don’t hesitate to go with it across the board. If the longevity of a bolt or breech O-ring actually proves to be a problem, it seldom can be laid at the feet of the material. More likely that the parts are rough and need to be smoothed, or there is a burr or other sharp edge that needs to be removed, or a misalignment that is putting undue stress on the O-ring.

When I need to purchase small quantities of several different sizes, I tend to use https://www.theoringstore.com/store/

For larger quantities (100/pk), I typically lean on McMaster or Amazon.
 
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Upvote 1
Gerry52 said:
Mcmaster-Carr is where I get mine, for years. All o-rings, metric & standard, all materials. If you have a caliper & can get the size I'm sure they'll have it. My last $10 order from them got me 50 o-rings. None of that $8 per ring BS. I hear Captain O-rings is another good source.
Click to expand...
Thanks!
nervoustrig said:
For 95% of uses in PCPs, Buna-N in 70 durometer is a great choice. For static O-rings in particular (O-ring stays in one place to hold pressure). When dealing with pressures above 3000psi, it may be necessary to step up to 90 durometer. Same can be true at lower pressures is the parts have loose tolerances (extrusion gap between parts is large).

For dynamic O-rings—those that are subject to abrasion—polyurethane is a better choice. For the most part we are talking about bolt or breech O-rings. Granted, Buna-N will also last a long time in the vast majority of cases so don’t hesitate to go with it across the board. If the longevity of a bolt or breech O-ring actually proves to be a problem, it seldom can be laid at the feet of the material. More likely that the parts are rough and need to be smoothed, or a there is a burr or other sharp edge that needs to be removed, or a misalignment that is putting undue stress on the O-ring.

When I need to purchase small quantities of several different sizes, I tend to use https://www.theoringstore.com/store/

For larger quantities (100/pk), I typically lean on McMaster or Amazon.
Click to expand...

God damn! Thank you for all this info, this is great!
 
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I've ordered from all three, The Oring Store, Orings and More, and off eBay with Captain Oring. Some orings and types of oring material is more expensive, but not $8.00 expensive for the sizes we commonly use.

As far as types of material and hardness of said orings, the common buna 70 oring will work in most applications. However, some airguns need harder oring materials in high pressure area and on moving parts such as with valve stem seals and the like. On valve stems I use polyurethane orings there, with special lube as well. Doing a search of what other's forum members use in that instance is best because your particular model may not "require" special application of orings or of lube (done for for higher performance usually).
 
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Airgun-hobbyist said:
I've ordered from all three, The Oring Store, Orings and More, and off eBay with Captain Oring. Some orings and types of oring material is more expensive, but not $8.00 expensive for the sizes we commonly use.

As far as types of material and hardness of said orings, the common buna 70 oring will work in most applications. However, some airguns need harder oring materials in high pressure area and on moving parts such as with valve stem seals and the like. On valve stems I use polyurethane orings there, with special lube as well. Doing a search of what other's forum members use in that instance is best because your particular model may not "require" special application of orings or of lube (done for for higher performance usually).
Click to expand...
What’s this specialized lubricant you use on poly o rings?
 
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i would again reiterate the suggestion to measure them, theyre almost all metric these days .. then ebay can be searched for the size and typically a bag of 5-10 can be scored for a couple bucks shipped .. captain oring haha, yeah they see ya comin, convenient maybe, but onc eyou got it you got it ... the format theyre listed as is IDxODxThickness .. the only ones that generally arnt clear are the tiny ones and those typically stretch lol, anything close ... but others, do the math if it seems unclear, 2 times the thickness + the id equals the od to double check ...
 
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No problem, I hope we can get you pointed in the right direction.

Regarding lubrication...and this isn't a response to your question about a special lubricant, but what applies for the other 98% of the time.

Use pure silicone anywhere O-rings slide on something. Silicone oil for dynamic O-rings...those that slide like a bolt or breech O-ring, fill probe O-rings, etc.. Silicone grease for static O-rings to aid with assembly and improve longevity.

Silicone oil is sold inexpensively as "silicone shock oil" for RC cars (sold in many viscosities...30 weight is a good choice for airgun use). Silicone grease is sold inexpensively as automotive dielectric grease.

Not only is silicone an excellent lubricant for O-rings, it is also non-combustible.

However do NOT use silicone where metal touches metal. It is a terrible lubricant for metal on metal.
 
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dizzums said:
theyre almost all metric these days
Click to expand...
For Evanix, of South Korean manufacture, yes. In some cases, a close match "dash" (aka standard or AS568) O-ring will work. Seeing quite a bit of that in searching Evanix O-ring sizes, e.g.:

Evanix parts and custom Help please.

I have seen a guy named Boris who has done some work on Evanix i have owned in the past,but do not know how to contact him. Any help would be greatly appreciated.
www.airgunnation.com www.airgunnation.com

dizzums said:
the format theyre listed as is IDxODxThickness
Click to expand...

Which can be confusing because the industry-standard way of calling out a metric O-ring is thickness x ID. So for example an M2 x 8 is 2mm thick with an 8mm inside diameter (and thus 12mm outside diameter).
 
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dizzums said:
i would again reiterate the suggestion to measure them, theyre almost all metric these days .. then ebay can be searched for the size and typically a bag of 5-10 can be scored for a couple bucks shipped .. captain oring haha, yeah they see ya comin, convenient maybe, but onc eyou got it you got it ... the format theyre listed as is IDxODxThickness .. the only ones that generally arnt clear are the tiny ones and those typically stretch lol, anything close ... but others, do the math if it seems unclear, 2 times the thickness + the id equals the od to double check ...
Click to expand...
My friend lent me his super fancy caliper so I’m good there 👍
nervoustrig said:
No problem, I hope we can get you pointed in the right direction.

Regarding lubrication...and this isn't a response to your question about a special lubricant, but what applies for the other 98% of the time.

Use pure silicone anywhere O-rings slide on something. Silicone oil for dynamic O-rings...those that slide like a bolt or breech O-ring, fill probe O-rings, etc.. Silicone grease for static O-rings to aid with assembly and improve longevity.

Silicone oil is sold inexpensively as "silicone shock oil" for RC cars (sold in many viscosities...30 weight is a good choice for airgun use). Silicone grease is sold inexpensively as automotive dielectric grease.

Not only is silicone an excellent lubricant for O-rings, it is also non-combustible.

However do NOT use silicone where metal touches metal. It is a terrible lubricant for metal on metal.
Click to expand...
Interesting, I wasn’t familiar with the difference between silicone oil and silicone grease. I got some super lube silicone grease with PTFE, I guess I’ll be purchasing some oil now as well. I have moly paste for the metal to metal, seemed to have superior characteristics to graphite.
 
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nervoustrig said:
For Evanix, of South Korean manufacture, yes. In some cases, a close match "dash" (aka standard or AS568) O-ring will work. Seeing quite a bit of that in searching Evanix O-ring sizes, e.g.:

Evanix parts and custom Help please.

I have seen a guy named Boris who has done some work on Evanix i have owned in the past,but do not know how to contact him. Any help would be greatly appreciated.
www.airgunnation.com www.airgunnation.com



Which can be confusing because the industry-standard way of calling out a metric O-ring is thickness x ID. So for example an M2 x 8 is 2mm thick with an 8mm inside diameter (and thus 12mm outside diameter).
Click to expand...
Yeah! I’d looked at that thread as well while researching writing this one. Thank you for clarifying the naming conventions for o rings
 
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Bernie7 said:
I got some super lube silicone grease with PTFE
Click to expand...
Please check that what you have is in fact silicone. The most popular Super Lube product sold in many stores marked as having PTFE is not silicone-based...yet is odorless and has a consistency and appearance very much like silicone, and therefore is often incorrectly believed to be silicone.

One example:
torch test - annotated.jpg
 
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I’d like to know what the numbers represent. I’ve been trying to source o-rings for a few guns and the o-rings sizes seem to be written differently. Some sites seem to write the cross section first and others the inner diameter first.

How am I to know if I’m ordering the correct size according to a parts list? Then I’ve viewed o-rings on sites that seem to have the sizes leading up to a size I’m seeking only mysteriously skip over a size that I need. Then I see many o-rings are less than a penny each and some cost exponentially more. Then there are o-rings with irregular sizes and weird hardnesses like 75 and 80. I know I’m tired of looking and only able to find two or three sizes from the same source. Any suggestions?
 
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A friend told me about this website today: https://www.o-ring-stocks.eu/
No idea if they ship outside the EU, problem is you need to buy many o-rings at once. Prices are good but you have to buy like 250pieces at once.
I have no idea on quality as I've never used them as today is the first time I've heard about them.
So do you want 1 o-ring for $8 or 250 for the same price?
336624200_653146096644928_5124056952101835526_n.jpg
 
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