Tuning All PCP owners need one of these

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Humdinger

Humdinger

Member
Jun 3, 2015
1,154
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Charlotte, NC, United States
One of the most common questions posted on airgun forums is "what size o-ring do I need for this"? Many of the PCP manufacturers don't publish schematics or parts lists with o-ring sizes because they either want the income from parts and service sales or they just don't want people to work on their own PCPs.

A digital caliper is a must have tool for all PCP, compressor, and tank owners. A caliper and an o-ring size chart allow anyone to size an o-ring and then reference it to find the replacement size they need. All metric o-rings are sized by their thickness and inner diameter. Many common metric sizes even cross reference to USA standard sizes which have an A prefix. For instance, a 1.5 x 5 metric o-ring has a 1.5mm thickness and an inner diameter of 5mm and an outer diameter of 8mm. The outer diameter will be the inner diameter plus double the thickness of the o-ring. 5 inner diameter plus 1.5 thickness x 2 = 8mm. There are many commonly sized o-rings that are found in USA standard and metric o-ring kits. Most o-rings found in PCPs are 70 durometer buna, with a few that are 90 durometer. The higher durometer number refers to the hardness for higher wear such as on pellet probes or barrel breach seals.

caliper.1631640508.jpg


All of this may sound confusing at first, but with a little research and willingness to learn, an owner can save themselves lots of time and expense by resealing their own PCPs, fittings, and tanks. I use a digital caliper to find the exact size of many parts and accessories in and outside of airgunning.

Here is an o-ring chart I have used many times. A caliper can cost as little as $10. It is a must have tool if you want to be independent and service your own equipment.

https://www.marcorubber.com/o-ring-size-chart-as568.htm




 
True . However once you have the size you probably will not be able to source the needed “O” ring from any supplier locally. The O ring store is about the best place once you have determined what you need. I have yet to see a manufacturer provide the information. Perhaps some do . I have purchase several “kits” containing standard and metric o rings only to find nothing that works. Charlie Frear provides O rings with his guns. He’s the only one I’m familiar with who does. BUT. The o ring store will get then to you pretty fast.
 
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True . However once you have the size you probably will not be able to source the needed “O” ring from any supplier locally. The O ring store is about the best place once you have determined what you need. I have yet to see a manufacturer provide the information. Perhaps some do . I have purchase several “kits” containing standard and metric o rings only to find nothing that works. Charlie Frear provides O rings with his guns. He’s the only one I’m familiar with who does. BUT. The o ring store will get then to you pretty fast.
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Agreed. Most o-rings need to be ordered online but there are many online o-ring suppliers. Many of the metric airgun manufacturer sourced o-rings have to be shipped from overseas. If you can size your own you can order more than a single o-ring without paying for an entire rebuild kit and shipping cost from overseas. However, if someone sizes their own o-rings they can buy a pack of them for less than a factory kit with singles. Over the years I've accumulated quite a few o-ring sizes. Additionally, Ebay is also a good source to get several odd sizes in larger than single numbers that a rebuild kit would supply. I recently rebuilt a Huma regulator and got packs of 5 metric sized o-rings that Huma would only supply one per rebuild kit.
 
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The other thing I've found valuable is the Harbor Freight O-Ring selection box. It's $8 for nearly 400 O-Rings in common sizes. Often enough, they don't fit, but once in a while one in the kit does fit and saves my bacon. Yes, I received a 74CF tank from PA, and the w-ring between the valve and tank blew. Sure enough, there was a 212 o-ring in the kit that saved the day. That one alone was well worth the $8

The other one is my Ninja fill station. It takes #6 O-rings. Worked like a charm.

Best thing is you can take the old o-ring and compare sized. They don't always match, but you can get a good idea what you are working with.
 
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..."Here is an o-ring chart I have used many times. A caliper can cost as little as $10. It is a must have tool if you want to be independent and service your own equipment.

https://www.marcorubber.com/o-ring-size-chart-as568.htm"...



Thanks for the link; it would have been helpful in past adventures. I expect it will be in the future.

I have become one of those who lives by a (paraphrased) maxum: "Why pay someone else $10 to fix something I can destroy myself after spending $20 for parts". Now I know exactly what sized o-rings I need so the thing can be trashed with functional o rings. No need to guess.

I keep a similar digital caliper always at hand and use it all the time. A tip - To convert metric to inch (or inch to metric) for whatever purpose, dial the value in on the caliper, and switch scales with a simple button push. Instant conversion.



JE, reporting from the Cascadia Subduction Zone
 
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