How to purge your gun, BEFORE or AFTER the regulator?

Jump to latest Follow Reply
SkeeterHawk

SkeeterHawk

Member
Oct 23, 2021
646
589
Florissant, Colorado, United States
Hello everyone!

I asked this question as a part of Nirinium's thread "How to de-gas a FX Carbon Fiber Bottle/Tank?", but I am afraid that it got buried. I spent some time searching the forums for this information and didn't come up with anything, which was surprising.

So, my question is, should you purge the air from your gun by releasing it BEFORE the regulator or AFTER the regulator? My experience has shown that you should purge after the regulator, even though one of my PCP kits has a plug for purging on the reservoir.

My evidence to back up this claim is that I am rebuilding my regulators much less often by purging through loosening the regulator gauge rather than using the purge-plug. In the thread above, I pose my theory that the regulators are designed for there to be a pressure drop AFTER the regulator by firing the gun, and the regulator will bring the pressure back up to the set-point. If you purge the bottle, the plenum will still have the working pressure until the differential gets so great that you will force air backward through the regulator (Tearing the heck out of the o-rings in the process).

Again, I have "official" real-world anecdotal experience with this, so I am interested to see if I am the only one that has come to this conclusion.

Jonathan

PS - My Avenger requires that you purge the gun before you reduce the reg pressure (As not to do damage), so this seems to support my theory.
 
Thanks for the feedback, Nervoustrig!

Maybe my guns are the "rare edge case". Most of the guns that I shoot most often are PCP upgrades to a 2240 platform, and my regulators and valves (so far) are from China. Perhaps if I went with a 90 durometer o-ring in the regulator instead of the 70 durometer, it may hold up better. When I first started messing with these kits, I didn't know any better, so I didn't dry fire the gun while purging the cylinder since it had a purge plug. Now that I understand the fundamentals better, I certainly would be dry firing it as it evacuated to equalize pressure across the regulator. That said, it is easier to purge it after the regulator slowly and just let it go.

Again, I am glad to get some confirmation of my theory. Since I am not always purging the tank instead of just topping it off, this doesn't come up a lot, but I definitely seemed to be getting a lot more shots in between repairs when purging after the regulator. Does anyone else have any evidence for or against this theory?

Thanks again for all of your input!
 
Upvote 0
My Avenger requires that you purge the gun before you reduce the reg pressure (As not to do damage), so this seems to support my theory.
Click to expand...

Oops, I also meant to comment on this caution from your Avenger manual. It is to prevent damage to the regulator's valve seat. When the system is pressurized, the two faces of the valve seat are pressed together. If at this time you dial the adjustment for a lower pressure, you are attempting to bring the surfaces closer to each other...except they can't get any closer without grinding them together and gouging the plastic seal. If damaged in this way, the regulator will usually develop a creeping symptom where the output pressure will slowly climb for minutes or hours after the last shot was fired, leading to a "cold" shot (first shot of the day) being off and generally wreaking havoc with the velocity spread.

But just as notably, it will NOT cause O-ring damage or leaks.
 
  • Like
Reactions: Jmac
Upvote 0
What you say makes sense. That is the same way that the Chinese regulators operate (as if there is a difference?). You turn it counter-clockwise (away from the regulator seat) to increase the regulator pressure, but you have to take the bottle off to adjust the regulator, so by default, there is no way to do what you said. Since the Avenger is externally adjustable, you could cause this problem of mashing the adjustment against a solidly seated valve. Thanks for the tip!

So, in my regulators, the o-rings are shredded when they give up. I'm assuming that this may be a durometer rating thing, then.
 
Upvote 0
So, in my regulators, the o-rings are shredded when they give up. I'm assuming that this may be a durometer rating thing, then.
Click to expand...

If they've developed little wings...wispy bits of material hanging off of them, that is the material extruding. In that case, yes a higher durometer will resist it better.

Here's an example...O-rings much larger than you'd generally find in a regulator but illustrates the extrusion wings:


 
Upvote 0
Now THIS is informative! That looks like a manufacturing defect, but in reality the o-ring is "extruding" into the gap that it is supposed to be sealing. Here are a couple pictures showing the damage:
20211112_124016.1640996930.jpg
20211129_174712.1640996931.jpg


You can see that the o-ring seems to "peel" back. This Green one does the same thing as the 70duro black ones, but these are the only pictures that I could find easily. Another thing to note is that the peeling isn't happening during my disassembly because numerous times there would be a piece of the o-ring down around the Belleville washers.

What I am seeing may still be the extrusion that you are talking about nervoustrig, but just a really severe case such that it is letting the rubber extrude all the way into the regulator. One more observation is that the extrusion is happening going toward the high pressure side, giving an indication that I may be seeing damage from the high pressure from the plenum going back through the regulator to the (now) lower pressure bottle side...or something similar.
 
Upvote 0
Yes sir, that damage looks like classic extrusion failure. In the second picture, we see the material being pushed toward the Belleville washer stack, which is at atmospheric pressure. High pressure air is on either side of that chamber so that dictates where the material will be pushed.

Definitely should try 90 durometer and see how that fares. With typical part tolerances, 70 durometer works fine for 3000psi operating pressure but sometimes the fit is a little sloppy and you have to step up to 90.
 
  • Like
Reactions: SkeeterHawk
Upvote 0
I really love The O'Ring Store! That place is great! It was right after this discussion that I ordered a WHOLE BUNCH of o-rings in different sizes and durometer ratings that are really close to the o-ring size for my regulator and valve. The FedEx dude got here with them about 6PM this evening, so they even got here a day early! Nice! To put the icing on the cake, they always put a piece of candy in with the order. I believe that this is my third order with these guys, but they have a customer for life if they keep this level of customer service up.

These o-rings got here just in time. It seems like my regular shooter is going to need an o-ring replacement soon as the regulator is starting to creep up really slowly over the last couple days. It has gained a couple hundred PSI since I did the Monthly Shooting Challenge on the 4th. I guess I will need to start taking better notes on what o-rings I am putting into these things and how long they last. As I said, my observations on how often that I am rebuilding them is rather anecdotal, but rebuilding them is a pain in the butt because it takes a while to get them tuned again afterward.

Since I have adopted this airgun hobby, I have acquired a TON of o-rings and compression springs. I have a whole tackle box full of them now that probably weighs 20 pounds. I can't be the only one with this "parts purchasing affliction".
 
Upvote 0
I hear you. My wife thinks I'm starting an O-ring distribution warehouse. When it comes to springs, I only have 2 storage boxes and 3 Cool Whip containers.

BTW if the regulator pressure is creeping up over a period of minutes or hours, don't pin it on the O-rings. Creep is all about the surface quality of the valve seat. If it has become dimpled and/or roughed up when viewed under magnification, dress it smooth and flat. Wet sand with progressively finer grits out to at least 2000 grit, using a suitably flat surface to back the sandpaper (granite countertop, thick piece of glass, etc.). Or if you have the option to knock out the plastic insert and replace it, you can go that route. For example, the Ninja brand paintball regulators have a little 4mm plastic ball that you can replace. The OEM one is nylon and wears relatively quickly...I made a habit of replacing them with Delrin:

https://www.mcmaster.com/9614K73

Many of the generic China-made regulators use something slightly more long-lived than chewing gum. They can be made to perform much better if you can machine a replacement...which quickly erases any potential cost savings over a quality regulator but if you have the skills and the time, it's an option.
 
Upvote 0
I hear you. My wife thinks I'm starting an O-ring distribution warehouse. When it comes to springs, I only have 2 storage boxes and 3 Cool Whip containers.
Click to expand...

LOL!! I've been rating all my springs for poundage of pull lately. The diameter of wire, coil density, etc., are meaningless to how hard it is to pull. I'd love to know more about how that is possible. For example, I've got a bunch of 0.042" diameter wire springs that vary from <1# to over 8# of pull. They don't look that much different, but "boy howdy" are they different on the hammer! You can't just roll into Ace Hardware and pick a spring and think it will "do it for you". This should be it's own topic.

What you suggested for cleaning up the seals for the o-ring is spectacular! Thank you! I will definitely keep that one in my pocket for this series of 2240 heartache and going forward. I think (so far) that the problem that I have is from your previous comment about the tolerances not allowing the 70 durometer to seal without blowing out. Every time I take the regulator apart, the o-ring is absolutely shredded. Perhaps polishing it will help once I use the denser o-rings, but for now I don't want to remove any more material and make the tolerances worse. I'll be buying a Huma soon for my regulator 22cal shooter. The main reason is that the Chinese regulators that I have just can't regulate consistently above about 130bar (1900 PSI). That is fine for my 0.177, but the 0.22 really needs a little more "horsepower under the hood".

The regulating seal on these regulators feels like Teflon. I have been really easy on them, and so far they are holding up without any marring or anything. It is just the rubber seals around them that are buckling. Hopefully the new plethora of higher durometer rating o-rings that I received in tonight will let me nip this problem off. I am still rebuilding my guns (anecdotally) about every 3 months, or around 2500ish rounds right now. This isn't terrible, but it would be nice to make that less often, and I hope that the higher duromer o-rings is the silver bullet.
 
Upvote 0
nervoustrig said:
Oops, I also meant to comment on this caution from your Avenger manual. It is to prevent damage to the regulator's valve seat. When the system is pressurized, the two faces of the valve seat are pressed together. If at this time you dial the adjustment for a lower pressure, you are attempting to bring the surfaces closer to each other...except they can't get any closer without grinding them together and gouging the plastic seal. If damaged in this way, the regulator will usually develop a creeping symptom where the output pressure will slowly climb for minutes or hours after the last shot was fired, leading to a "cold" shot (first shot of the day) being off and generally wreaking havoc with the velocity spread.

But just as notably, it will NOT cause O-ring damage or leaks.
Click to expand...
Good Call!, Spin, - Retired machinist and valve mechanic (it may be possible to lap in damaged seats and get full shutoff again) I haven't tried it but it seems
very doable. Just about all high end critical service valves using plug and seat ring are lapped in.
 
Upvote 0
it may be possible to lap in damaged seats and get full shutoff again
Click to expand...

Yes sir, many of us have fixed creeping regulators by dressing the seat smooth and flat. FWIW, I don't usually lap the parts together because the seat geometry of most regulators produces a stress concentration that will pretty quickly iron a good mating surface into the plastic part after it has been cycled a modest number of times and left idle. Otherwise yes lapping them together will speed along the break-in period.
 
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu