Strange Automag Issue

[Toestr]

I recently rebuilt an automag and I was using an old CO2 tank to check for leaks (no air at the moment). I was filling a remote line with CO2, then closing the valve on the tank to avoid draining it in case of leaks. I aired it up with just the CO2 in the remote line, and it initially leaked out the front 'OIL' hole in the bottom of the valve, but after turning the velocity adjuster in it was fine. I then opened the tank valve and it immediately started venting out the overpressure valve. I tried this a few times and each had the same result.

I think I have a pretty good setup to keep liquid out (tank oriented vertically, remote line, expansion chamber). Obviously mags and CO2 aren't best friends, but it is doable. Any suggestions?

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[superman]

My guess is the velocity is either turned up too high or your reg piston is toast.

[punkncat]

Many people don't realize that there is a piston inside the back, under the spring pack. I agree with Jake.

[Toestr]

My guess is the velocity is either turned up too high or your reg piston is toast.

Reg piston oring was just replaced and was regreased along with the springpack. Do you mean the overpressure vent?

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[superman]

The entire reg piston assembly, not just the oring on the piston.
Inside the piston is a urethane seal which overtime goes bad and will leak. They are not user serviceable as they are set to a specific blow off pressure.

[Jordan]

Reg piston oring was just replaced and was regreased along with the springpack. Do you mean the overpressure vent?

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The vent is part of the piston... it's not advisable to take them apart as there are no service parts inside, but if you were to take it apart and flip the disc inside, purely for testing purposes, I see no harm in it.

They are available from AGD as an assembly.

[Toestr]

Ok, so I put both the piston and entire on/off assembly in from my other automag, which was confirmed working as of 2-3 weeks ago. I'm not getting it venting from the overpressure valve, but it is still leaking out of the holes for mounting a backbottle ASA. Same deal, leak gets better when screwing in the velocity adjuster to a point, then gets worse.

Edit: also changed out the reg seat, no difference.
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[Jordan]

If it's leaking here...



Then to me, it has to be either the piston oring, or an irregularity inside the reg back that's preventing a proper seal.

OR, the oring between the valve halves is leaking.

[Toestr]

If it's leaking here...



Then to me, it has to be either the piston oring, or an irregularity inside the reg back that's preventing a proper seal.

OR, the oring between the valve halves is leaking.

Yep, looks like the piston oring is getting sliced on insertion. Odd because it doesn't feel like I'm scraping the wall particularly hard or anything. Any recommendations for cleaning up the reg ID? Emery cloth?

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[Jordan]

Yep, looks like the piston oring is getting sliced on insertion. Odd because it doesn't feel like I'm scraping the wall particularly hard or anything. Any recommendations for cleaning up the reg ID? Emery cloth?

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Is there a burr somewhere that you can see?

[Grendel]

and make sure you grease it up liberally.

[Toestr]

Is there a burr somewhere that you can see?

No, the threads around the rear OIL hole might be a bit raised, but that's a might. It's definitely the piston orings though. I tried 3 factory spec orings and I'm 3 for 3 on cutting them.

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[Jordan]

Like Grendel mentioned, a liberal dose of grease should help. I'd be leary of honing it out too much and creating other issues.

You could try a softer buna oring, sometimes the harder durometer seals have a hard time "giving" over an interrupted surface like that. It's virtually a static seal, so you should be ok.

[MrBarraclough]

I second the buna suggestion.

[Alexndl]

I have a ans Phase II reg back for really cheap if you are interested to try to change the part

[Toestr]

Update:

I disassembled the reg and tried putting the piston with oring in in a specific orientation to determine which part of the body was cutting the oring. No cuts on the oring at all. Did this on a few times, still no cuts.

I got some HPA and filled the remote line and then closed the tank. Air up the gun form the remote, no leaks. I open the tank with the remote still attached, and it immediately leaks from the oil holes. Again I tried airing it up with just air in the remote, no issues. I try with the tank open, leaks.

What would make it leak only at full tank pressure?

Below are some pictures of where the orings have broken in the gun. They look like scalloped cuts around the outer diameter. They are good quality new orings from the oring store, which I've also used in my other mag without issue.
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[Toestr]

It was the Seat! The guy I got if from said he put a fresh seat in, but that doesn't work when it's the wrong one. The opening is bigger on it (right) than a proper mag seat. I'm guessing this one is for an ANS or AA reg.

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[MrBarraclough]

So what exactly was the mechanism by which this improper reg seat was causing the reg piston o-ring to get chewed? I'm guessing that it was allowing air to bypass the reg seat and thereby subjecting the piston o-ring to full tank pressure, pushing it against the internal threads of the reg body. Is that it?

[Jordan]

It might even be a Cocker cocking rod bumper... they're about the same OD.

When you said rebuild i figured you included a fresh reg seat. Glad you got to the bottom of it, though.