EVOL Foster fitting leak

[Dairyboy]

I've heard people have issues with the foster fitting check valve sticking open, myself included. A quick drop of silicone oil in the foster fitting and a fill was a nice bandaid fix that did last me quite some time. I tore my gun down last night to remove any silicone oil/grease and lube with Ultimox on Tom's recommendation as I did a reseal a couple months back but used silicone grease. Well this morning I noticed my gun leaked from 3500psi to 1000psi over night. Alittle soapy water and it was the foster check valve. Well these are quite easy to change. Just need a 1/8 allen wrench, a -004 90 duro poly oring, and a 1.5x7mm 70 buna.
Simple though you just need to degas via loosening your burst disk, some under the chassis if newer, mines on the side. Then simply remove the foster fitting and will come out like this.

Remove the check valve

Hard to see but mine was full of cracks and when removed it was brittle and crumbling.

Getting the new one on was difficult. Just the initial getting it started was hard but once it was slid on easy. While there I also replaced the oring that sealed the foster fitting to the gun. Simple and straight forward to do. Lightly lubed both with ultimox and now good to go.

I'd recommend everybody buy the assortment of orings for the Evol in case something does come up that you don't need to wait as you'll be prepared. There's not very many orings in the gun and I bought I think 10-20 of each from the oring store for maybe $50? Do it for all my guns the last few years. Doesn't hurt to have them on hand! And those that have had an issue with the check valve, I'd get some of those orings as yours might be brittle and starting to crack like mine.

 

[Bladebum]

Great write up. I really like how this forum has become basically the hub for information on the Evol and AAA guns. When I bought mine there was such little info out and now we are building a plethora of posts from repairs and quirks of the gun to improvements, upgrades and strong points. Makes my favorite gun and brand that much more my favorite!

 

[Pnwairgunner]

Is there a complete o ring list size already posted for it? Seems like I saw one but can’t recall where.
I try to keep extra o ring kits for everything I own and I like to put them in small ziplock baggies with a drop of silicone oil to keep them from deteriorating over time. (Yes I’ve also bought Ultimox lube to use to lube the Evol.) And I write on the outside of the ziplock what airgun it is for.
I need to get my butt in gear and buy some spares for the Evol and for my Notos for sure.

 

[Dairyboy]

Great write up. I really like how this forum has become basically the hub for information on the Evol and AAA guns. When I bought mine there was such little info out and now we are building a plethora of posts from repairs and quirks of the gun to improvements, upgrades and strong points. Makes my favorite gun and brand that much more my favorite!

Yes that my hope that if anyone needs anything Evol just come here and you should find your answer!

 

[Dairyboy]

Is there a complete o ring list size already posted for it? Seems like I saw one but can’t recall where.
I try to keep extra o ring kits for everything I own and I like to put them in small ziplock baggies with a drop of silicone oil to keep them from deteriorating over time. And I write on the outside of the ziplock what airgun it is for.
I need to get my butt in gear and buy some spares for the Evol and for my Notos for sure.

Here's the oring list

https://americanairarms.com/wp-content/uploads/2022/11/EVOL-O-ring-chart.pdf

I need to get some for my Notos also lol. Only 2 PCPs I own but I don't have them for that yet.

 

[Pnwairgunner]

Awesome… yep as soon as I saw the attachment I realized I’ve got it saved in my files already. Thank you much. If you find a list for the Notos I need it as well … haven’t seen it anywhere yet.

 

[Pumacarl]

Actually, I believe the single most informative thread for the Evol was started by Ezana4CE over on Airgun Nation. Here's the link:

American Air Arms - All Things EVOL - Master Thread

This thread is dedicated the the American Air Arms Evol. A while back someone posted asking for a thread like this. I thought that it seemed fitting to compile Evol threads, information, videos, photos, and questions in a single thread for easier reference. This will take some time to do. I am...

www.airgunnation.com

It is good to have this info at more than one forum. I really like back-ups, one is none, two is one.

 

[Pumacarl]

Dairyboy, thanks for posting this information! Since mine already stuck open on me twice already, I will be changing my o-rings out when I eventually get the 42cc plenum. I was going to wait until it failed, but not after seeing your picture of the o-ring being dry and cracked. A picture does say a thousand words.

 

[One-Shot]

I've heard people have issues with the foster fitting check valve sticking open, myself included. A quick drop of silicone oil in the foster fitting and a fill was a nice bandaid fix that did last me quite some time. I tore my gun down last night to remove any silicone oil/grease and lube with Ultimox on Tom's recommendation as I did a reseal a couple months back but used silicone grease. Well this morning I noticed my gun leaked from 3500psi to 1000psi over night. Alittle soapy water and it was the foster check valve. Well these are quite easy to change. Just need a 1/8 allen wrench, a -004 90 duro poly oring, and a 1.5x7mm 70 buna. View attachment 1969View attachment 1970
Simple though you just need to degas via loosening your burst disk, some under the chassis if newer, mines on the side. Then simply remove the foster fitting and will come out like this.
View attachment 1973
Remove the check valve
View attachment 1972
Hard to see but mine was full of cracks and when removed it was brittle and crumbling.
View attachment 1971
Getting the new one on was difficult. Just the initial getting it started was hard but once it was slid on easy. While there I also replaced the oring that sealed the foster fitting to the gun. Simple and straight forward to do. Lightly lubed both with ultimox and now good to go.

I'd recommend everybody buy the assortment of orings for the Evol in case something does come up that you don't need to wait as you'll be prepared. There's not very many orings in the gun and I bought I think 10-20 of each from the oring store for maybe $50? Do it for all my guns the last few years. Doesn't hurt to have them on hand! And those that have had an issue with the check valve, I'd get some of those orings as yours might be brittle and starting to crack like mine.

To get the oring on, I used a socket from a socket set. Used one with just enough clearance for the valve stem to enter, but with a small enough diameter to allow the oring to sit on the lip. Just pressed the valve stem through the oring and it was done in 2 seconds. Took me 20 minutes to find what I needed though

 

[Dairyboy]

Awesome… yep as soon as I saw the attachment I realized I’ve got it saved in my files already. Thank you much. If you find a list for the Notos I need it as well … haven’t seen it anywhere yet.

I haven't either. I should look around....

 

[Dairyboy]

Actually, I believe the single most informative thread for the Evol was started by Ezana4CE over on Airgun Nation. Here's the link:

American Air Arms - All Things EVOL - Master Thread

This thread is dedicated the the American Air Arms Evol. A while back someone posted asking for a thread like this. I thought that it seemed fitting to compile Evol threads, information, videos, photos, and questions in a single thread for easier reference. This will take some time to do. I am...

www.airgunnation.com

It is good to have this info at more than one forum. I really like back-ups, one is none, two is one.

That is a very good thread also. Lots of info there. Hard to get through it all though. But like said 2 places very valuable!

Dairyboy, thanks for posting this information! Since mine already stuck open on me twice already, I will be changing my o-rings out when I eventually get the 42cc plenum. I was going to wait until it failed, but not after seeing your picture of the o-ring being dry and cracked. A picture does say a thousand words.

Yeah I was surprised to find it cracked and dry. But yeah if your going in you might as well do it

 

[Dairyboy]

To get the oring on, I used a socket from a socket set. Used one with just enough clearance for the valve stem to enter, but with a small enough diameter to allow the oring to sit on the lip. Just pressed the valve stem through the oring and it was done in 2 seconds. Took me 20 minutes to find what I needed though

That's very smart lol wish I would have thought of that. Had a bunch of sockets literally within reach when I did it on my work bench.

 

[One-Shot]

That's very smart lol wish I would have thought of that. Had a bunch of sockets literally within reach when I did it on my work bench.

I’m going to 3D print a tool to do it. Essentially just a pusher tube that I can put in my tool kit.

 

[Ezana4CE]

@Dairyboy Although I have no idea where my leak is coming from, your post has given me a little more courage to attempt to reseal mine. I just hope that I have the necessary o-rings. There were a couple that I didn’t get when I ordered spares iirc.

 

[Bladebum]

@Dairyboy Although I have no idea where my leak is coming from, you’re post has given me a little more courage to attempt to reseal mine. I just hope that I have the necessary o-rings. There were a couple that I didn’t get when I ordered spares iirc.

The Evol is seriously easy to work on and diagnose leaks. The main culprits being the front block with the foster, gauge and main tube seal, and on the other end is the reg gauge seals and the two on the regulator. You can degass, tear the gun down, replace all those seals and air back up in 20 mins. RARELY is it ever valve or regulator internals leaking, atleast I never hear about it or experience those leaking myself.

 

[BanjomanMI76]

To get the oring on, I used a socket from a socket set. Used one with just enough clearance for the valve stem to enter, but with a small enough diameter to allow the oring to sit on the lip. Just pressed the valve stem through the oring and it was done in 2 seconds. Took me 20 minutes to find what I needed though

Wouldn't you like to know how they get them on at the factory???

 

[One-Shot]

Wouldn't you like to know how they get them on at the factory???

Do you have that information by any chance?

 

[Madeintheuk]

I put them in boiling water for a few mins to supple them up, and they pop straight on.

 

[One-Shot]

I put them in boiling water for a few mins to supple them up, and they pop straight on.

Only issue with that, is that they don’t necessarily return to net memory, so it may be necessary to drop the part and o-ring once assembled, back into the hot water to allow the rubber to now shrink back to net memory upon extraction and cooling. Common cause and effect.

 

[Madeintheuk]

Only issue with that, is that they don’t necessarily return to net memory, so it may be necessary to drop the part and o-ring once assembled, back into the hot water to allow the rubber to now shrink back to net memory upon extraction and cooling. Common cause and effect.

Never had that problem. Good info.