O-ring size/reference chart to scale, info needed for resealing anything

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JamesD.

JamesD.

Member
Dec 9, 2015
2,560
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NE PA, United States
Standard SAE
https://catalog.precisionassoc.com/asset/PAI%20Standard%20O-Ring%20Dimensions%20&%20Illustrations.pdf

Metric & specialty

https://catalog.precisionassoc.com/category/precision-associates-inc-o-rings?remote_addr=108.162.245.30&x_forwarded_for=157.55.39.167&remote_addr=108.162.245.212&x_forwarded_for=207.46.13.62

McMaster-Carr: What O-ring materials are best for my needs?

https://www.mcmaster.com/viton-fluoroelastomer/

The O-ring store: What's the difference of Static & Dynamic?

https://www.theoringstore.com/store/index.php?main_page=page&id=38&chapter=

!!WARNING ⛔️: Do not try to fix/alter/modify anything that voids warranty, you're not qualified, or 100% sure of when it comes to PCP's or Springers while under HPA (High Pressure Air) or preload tension of main piston spring. 
Author of this post is not accountable for any mishaps, damage to property, injuries, or deaths, whatsoever, should anyone take it on their own to utilize this information!!

Remember this; Professional tuners/Airgun Smiths are praised & recommended by the experienced members of the airgun community for good reasons. Utilize this forum and ask before you do anything that you aren't sure of or comfortable with as there's no shame in admitting that we don't know. Rule #1: Be smart, be safe.


I gave more examples for folks in a reply below but this top post is the technical info. A few things I didn't cover, and know will be asked.

A schematic of your airgun in need of repair should be acquired via the manufacturer or sought out on the forum. 


You could spend $7.99-$18.26 on bottled leak detector but all you really need is a few drops of dish or hand soap and a small clean paintbrush. A leak will reveal itself once the soapy water is applied to the areas in question.
Some top tuners have large blueing tanks so action can be submerged in water while under MSWP (Manufactures Safe Working Pressure) and observed very closely for a given period of time, as very slow leaks are harder to detect. 

In fact, if it's a slow (leaks from say 3K down to 2700 over a week or longer) leak in an older airgun that's had no recent maintenance that may have caused damage to a O-ring (slight knick or debris) then I suggest that 1 drop of https://www.pyramydair.com/s/a/Crosman_Silicone_Chamber_Oil/311

be introduced at the fill nipple and blown through the sintered filter & check valve during the fill. Shoot it down, refill, repeat. Fill to MSWP & let sit in stable environment and compare the previous air loss to time. If less air is leaking but still leaking, try another drop in the fill nipple and blown throughout. If this process doesn't fix the possibly dry, shrunken ring, it's time for a replacement. A drop to say 4 at most is not going to hurt a non regulated airgun. But it's a simple fix for some that have just sat too long unused. 
The Crosman Silicone Chamber Oil should not be confused with the Pelgun Oil they offer.

https://www.pyramydair.com/blog/2007/10/b-b-was-wrong-the-story-of-crosman-pellgunoil/

I'll be updating this post for more useful information as I have time. PM me or other known helpful members if you aren't getting answers to your posts. 








 
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Reactions: Chuck-in-Ohio, L.Leon, B and 1 other person
 Remember this though fellas. This chart is useful in say a resealing kit scenario. Where some of the O-rings are listed, while others maybe left out of the schematic leaving us with that "what in the world" look on our faces. 


Also consider that when we remove an O-ring, it's been deformed by set pressure, friction/ temp change wear. These circumstances can make knowing the correct size indeterminable between close variance of SAE, Metric, British, or others not common to AG's. If a company doesn't provide a schematic with parts inventory, we must at least know the standards used.

I experienced this recently with the 2 Condor breech O-rings. I took mine out after seeing extreme wear and gap between barrel and thought closest thing I might have is 7.9mm x 1.9mm. Wrong. It's a SAE #011 05/16" x 7/16" x 1/16" Buna Nitrile 70 Durometer for OEM breech. Aftermarket parts? I have no idea if parts came from PCP World, EBay, Alibaba, etc. and I didn't buy this item new, hence the misconception of Metric over the correct SAE. 

Also, 70 Durometer is most often the near perfect hardness we need for them to seal. 90 Durometer is used in some cases. 
https://www.theoringstore.com/store/index.php?main_page=page&id=38&chapter=6



https://www.sspseals.com/blog/what-is-the-difference-between-static-and-dynamic-orings

You're better off reading up on the many different materials O-rings are made of, and why. Then just buy a basic SAE or Metric kit of the material you desire. Most affordable common kits are 70 Durometer Buna Nitrile. 

While most Airguns do use good O-rings, they aren't always the absolute best for the application.
They're far from Aerospace Grade ones meant to never fail. In all fairness, no assembly line cut glands are going to be cut to Aerospace Grade tolerance, so no need for Mil-Spec.

When I mention Aerospace Grade, like NASA, Mil-Spec O-rings. It can and has been done in the AG application. Only person I'm aware of is Chip Smith. You noobs may not recognize that name but he's the guy that built The Sumo AG. A Rapid on steroids so to speak, and Chip's work was simply as good as it could possibly be done. He's moved on to bigger things but I would love to own one. When a guy has the ability to machine with in 1 micron, that's when Mil-Spec O-rings would be worth utilizing.
https://pimpmyairgun.com/viewtopic.php?t=857


This is just an example on O-rings and why they fail. Most common comparisons I can explain for educational purposes. 


Consider any factory springer piston seal. Or Jim Maccari aftermarket PTFE piston seals or variants that can take 3x's the heat of some factory types. That's an example of an O-ring/seal dealing with friction and sealing. 

Hand pumps. If you buy a Hill hand pump I can guarantee you will only ever have to replace 3-4 O-rings that are subjected to both high pressure and an extreme amount of friction. We solve this by using 100% pure silicone grease in the right amount, in the correct places. When you service any hand pump you will see that the pure clear silicone grease has turned black. It's from the wearing of those 70 Durometer Buna Nitrile rings. The little green PTFE on main piston seal is a higher quality O-ring as the mechanism places the high pressure output and heat on that part. 





 
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Hello all,

I just wanted to add this gentleman's work. All credit goes out to Phil on the following extensive lists. Invaluable information.

Notice how the 3 stage pump uses standard, metric, Japanese Imperial on what I would think is all metric. I'm only posting on the topic because O-ring maintenance is absolutely crucial to any airgun or fill system working reliably. Not sure if a link can be put here per the rules so please just copy & search:

A Airgun O-ring Database Credit to Phil

https://www.airgunnation.com/topic/oring-database-what-im-doing/

Credit to Dirte


Maybe one day this stuff will be easy to find.
 
Upvote 0
To add to JameD.’s post. To get a reference as to what size o-ring is required for a specific o-ring groove, you can use the S.A.E. chart as an example. American o-ring sizes have the required compression or squash built in to there size. For example: 1-014 o-ring, 1/2 by 5/8 with 1/16 (.0625”) cross-section. These are the sizes, 1/2 & 5/8, that the o-ring is to seal between. Then there is the actual o-ring cross-section of .070”, which gives you a compression / squash of .0075” per side for a total of .015” to give the o-ring it’s initial static seal. Note: Metric o-rings are actual size listed, so you need to calculate the amount of compression. The compression amount, (cross-section difference), on S.A.E. O-rings increases with cross-section size.
Probably as clear as Mud, but just trying to shed some light.

Keith
 
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