Air Venturi Regulator creep

[Aslap]

Avenge X in 25 cal. The rifle 3 months old and has about 500 pellets through it. I had noticed that the regulator seemed to be creeping a lot more than it should. Using the analog gauge, I had the setting at about 160 bar. Overnite the Reg would creep up to around 200 bar.

Putting on a digital gauge showed that to be the case. Reg was actually at 165 bar. Overnite it rose to 205 bar. if I fired a shot, the reg would come to a kind of stable point at the 165 number but it would be creeping upwards constantly at a rate of roughly 1 bar/10 seconds.

I pulled the regulator looking for any issues. As far as I could see, the plenum seat and the piston seal looked ok. The o ring on the piston looked a bit dry so I lubed that. I also cleaned off the seat and the seal.

Pumping back up and setting the reg again to 165 it appeared that the creep was reduced. Leaving it overnite , the reg creeped to 183 bar. When I fired it, the reg seemed to settle at 155 bar.

Does this seem normal? Maybe the piston seal is janky somehow? Perhaps this regulator set up just works like this? If I was shooting the rifle, I would certainly be sending the pellets out at pretty much the same pressure unless I waited a really long time before shooting. It should be said that my last shooting, I was getting the 25 grain JSB’s at 920 FPS with a SD of 4.5. That seemed pretty good so maybe that’s all I should be worried about.

Tony

 

[nervoustrig]

Pumping back up and setting the reg again to 165 it appeared that the creep was reduced. Leaving it overnite , the reg creeped to 183 bar. When I fired it, the reg seemed to settle at 155 bar.

That works out to about 18% pressure creep. I prefer to see something in the ballpark of 10% or less. The overwhelming majority of PCPs with a conventional knock-open valve (like the Avenge-X) will produce a very stable velocity if the hammer strike is adjusted to deliver about 97% of maximum velocity. For more reading on this topic, see this thread about Setting hammer spring tension on a regulated PCP or search the term velocity knee.

Ultimately, what matters is that you are getting a sufficiently low extreme spread for the type of shooting you do, meaning:

1. targets vs. plinking vs. hunting/pest control
2. maximum distance you're shooting (i.e. vertical dispersion you can accept at that distance)

So for example if you're not using it for hunting, you can always fire a clearing shot to reset the regulator and can therefore tolerate a bit of pressure creep. It's more of a nuisance than a problem. But if you've waited 3 hours in a hide to take a shot at a hog at 60 yards, it's a real problem.

As far as I could see, the plenum seat and the piston seal looked ok.

If you want to improve it further, that's the area to focus on.

Regulator creep, contributing factors, and how to deal with it

 

[Aslap]

Nervous,

Thanks! I don’t hunt and the rifle is destined for an easy life shooting at my home 25 yard range at clay pigeons and then the pieces of the clays and the pieces of those pieces……….until only dust is left. I may try to get it out to the real range at 50 yards when the weather breaks.

I feel better about this situation now. I may try and sweet talk AV into sending me a new piston seal just to try that out. The plenum seat is going to stay as is. I don’t want to try getting in there with any kind of spinning abrasive And have something go horribly wrong.

I‘ll read the links. I tuned it up by just setting the reg pressure and gradually adjusting the HS tension until the velocity topped out, then backed off the HS about 1/4 turn. The velocity come in at the 920 number and that seems to be the kind of velocity that I see giving good results with the JSB 25 grainers. At 25 yards I’m getting pretty good groups - .2 to .3’s shooting off a very shaky rest set up.

As an aside, I bought a Nate chrony and I am very impressed with that! So much easier to set up than my 40 year old F1 Shooting Chrony! Has not missed a shot and the web based app is a breeze to use. I need to learn how to get the shot string out of it and into Excel. Probably fairly easy.

Tony