Question from a new PCP user

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Weevil,

I found that hole and all is clear there.

Another tip off here - I just put the regulator back together with the spring stack popped into place. Prior to this it was really, really hard for me to get the ASA open/close valve to open the bottle all the way. I just wrote this off to pressure. Wrong. With the re-installed spring stack, the open/close action is as smooth as silk! I'm hoping this is it.

The reg is the standard one that comes on all of the 13 ci bottles. I got mine from Tippman but they all look the same to me. I watched You Tube from a guy who showed how to bump the reg pressure from the standard 850 to a higher pressure using Belleville washers and shims. When I opened my reg , I was surprised to see the Belleville stack already in there. So you can just used shims to take the reg to where you want it. on mine, a 0.020" shim got 1500 psig.

Tony
 
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Weevil,

I had to try it! Here's what it looks like. I think this is better. Maybe I'm overthinking this. This is a basically a Crosman being pushed with air. This is 40 shots with a drop of 3.2%. Maybe that's the best this rig is going to do. Next step will be to get the regulator pressure up some more to see what happens. There may be some kind of sweet spot here vis-a-vis pressure and hammer hit and valve spring. I still would expect. though, to see some sort of flat area and not this consistent drop in velocity.

Tony

Velocity v shots 14 gr rebuilt regulator.JPG
 
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Weevil,

I did add another shim and saw the velocity go up. However this graph tells the tale. I shot the bottle down to around 1500 and then refilled the bottle back to 3000 psig. The velocity went right back up and started dropping immediately. I think this proves there is no regulation taking place. I'm going to contact Tippman and send them some data to see what they have to say. These regulators are really simple devices and I'm at a complete loss as to what might be happening.

Weevil - what would you expect to happen if I mess with the reg hole?

Tony

Velocity v shots with tank refill.JPG
 
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Tony,

If you discount the first couple shots, it’s really not that bad. After all, these are not the worlds finest regulators.

Take a look at this article, particularly the graph “examples of various tunes…” and the paragraph below it.

hardairmagazine.com

Tuning Regulated PCP Airguns - Hard Air Magazine

The first thing you need to understand when tuning regulated PCP airguns is that for any PCP there is a maximum velocity for a given pellet,
hardairmagazine.com hardairmagazine.com

What you have is consistent with a tune at the plateau (blue line), right?

As I recall, it’s difficult for you to change the hammer, but if you push the reg up a little by shimming (say 100psi) you should drop below the plateau and hopefully get more of a flat line.
 
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Weevil,

I did bump the reg pressure but had the same results. When you get to his graphs with the shot strings, he definitely has good regulation going on. My results show direct correlation between bottle pressure and pellet velocity. That should not be the case.

I found a good video on how these simple regulators work. It seems like the piston does not move back against the seat after a shot is taken. There is some kind of restriction in the valve so that what is delivered to the SafePak is not the full bottle pressure but the pressure to the SafePak is varying along with the head pressure. I could try bumping the regulator pressure higher but it looks like that makes the problem worse. That first test at the 1500 reg setting shows beginning to end velocity variations of 10%. The lower reg pressures are dropping around 3%.
 
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This is more like it! Got a new bottle today. Left the reg where it is supposed to be set at 800. Filled to 2000. This is what I expected to see. Movement above and below some center point with minimal deviations until I fall off the reg and then things start to drop nicely. Tippman hasn't gotten back to me yet so I'm hoping that they get me a new bottle under warranty. I figure I was dropping off the reg starting about shot 21. At the very end, the gauge was showing under 500. I don't put much faith in that number though. Although, that SafePak has a 30 cc volume from what the maker told me. That may be acting as some sort of super buffer ahead of the valve. Perhaps 2 more shots would have dumped everything. I'll have to do that at some point.

As soon as I got this new bottle, I opened up the reg and got a look at the valve seat. This one is very nice and smooth all the way around the edge. The sealing material on this one appears to be some sort of softer polymer as opposed to the hard nylon on the Tippman tank. I found a great video that explains how these simple, single stage regulators work. After watching that, it became apparent that either the piston assembly was stuck somehow of the piston assembly was not sealing all the way.

Weevil - thanks for the help and the tips! I'll start to adjust the reg pressure upward from here. My goal is to get the 18 grain pellets at that 880-900 fps range. Any good tips on how I can calculate how much air I'm blowing on each shot? That would seem to be another kind of nice to know thing.

Tony

083123 new bottle.JPG
 
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Regulator with 0.01" shim and a start fill of 2000. If this regulator is anything like the other one (and I'm betting it is) then the reg pressure should have been around 1000, The velocity starts to fall right at the time the bottle reg got to 1000 at shot 16. This is also showing a lot less deviation while on the reg at this higher reg pressure. This is all done still using the 14 grain pellets. I'll add a 0.005" shim that should get the reg pressure to around 1200. Man, I'm learning a lot here fooling around with this! Still a complete neophyte but I'm starting to see how the various parameters are affecting each other.

Tony

0.01 shim 2000 start.JPG
 
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Glad to see that it’s working better. The efficiency is usually determined as fpe per cubic inch air used, but if you’re just comparing tunes on one platform then it makes sense to compare fpe obtained from your fill pressure to some set point before dropping off the reg. I assume you’re want to do this in order to find out when you’re reaching the limit in terms of fpe, at which point the efficiency will plummet. You’ll know when you’re pushing into that area because things will get noticeably louder!
 
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It's always something!

I added another shim to the spring stack and got a 60 fps reduction in velocity! What?

Turns out the new regulator (Valken) has a slightly different valve than the Tippman. The Valken spring stack is shorter and uses 8 thinner Bellevilles (0.025" thick) and two thicker Bellevilles (0.037" thick) on the outside of the 8 Belleville stack. This stack will go no higher than 1000 psig. I believe that when I added that last washer, That was just enough to keep the stack from sealing on the valve seat properly. Even with the low velocity, I had that same sort of constant dropping of velocity from shot to shot.

Fortunately, I had on hand some thicker Belleville washers at 0.032" thick. The Tippman stack allowed for 12 of this size washer but the Valken stack would only allow for 10. I installed those and went back to my regulator checker and now had 1300 psig on the reg. Well, it's 1300 psig on the gauge I have on my checker. Here are the results from the test this AM. Total FPE over the 40 regulated shots is 820 FPE. Again staying with the 14 grain pellets for consistency. At this pressure the shot-to-shot variation is getting better. Next step is to change out one of my 0.032" washers for one of the 0.037" jobs to see where that takes the reg. That may give me the 1500 psig I'm looking for. And that softer seal material I thought was in the Valken valve is just as hard as the Tippman material. The valve seat on the Valken cylinder is a lot smoother that the seat in the Tippman. Still not sure why I keep getting fairly high power shots when I'm so far off the reg. The last couple of shots here were at a 500 psig reg indication. I'll have to eventually shoot until there is no air left.

Tony

Velocity v shots big Bellevilles 1300 reg 14 grain.JPG
 
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I managed to to get 11 of the 0.032 Bellevilles in the stack. 1st part of the graph ir 14 gr Crosman premier HP. Where the velocity drop occurs I ran out of those and switched to the Crosman 14 gr Ultra Mag domes. Looks like they weight more than the HP's.

Anyway. the response is worse. I think I may have gone beyond what this valve likes in terms of length with the extra washers. I'm going back to the 10 Belleville stack since that was the most consistent. I'll take the small velocity drop and gain the consistency any day of the week. I also have to begin to track more closely where the regulator us set. The gauge on my checker says X but the gauge on the bottle is X minus some amount. I need to know on the bottle gauge just where the reg pressure is set and don't worry about the absolute value. I'm going to need some sort of better pressure gauge!

Tony

11 big Bellevilles reg at 1600.JPG
 
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Weevil,

There may be but that's someplace I don't want to go right now. I went back to that 1300 psig reg pressure and I found more of the Crosman 14.3 grain HP's so I reran with that and it looks pretty good to me. I can't really get above that 1300 psig mark with this valve. I know that the Tippman setup got me 1500 no problem. If I get a new bottle from Tippman I'll try bringing the pressure up. I'm very happy with this now! I'm not planning on taking my Crosman 2260 conversion to the air rifle international finals so all is A-OK with me. I'll do some accuracy testing over the next few days and run the numbers on the 18 grain pellets. Over the 40 shots that I would consider regulated (probably more like 38) the total FPE was 990. Better than before but I was getting a bit more velocity. I had to rebuild the valve stack again so different washers/arrangement? Maybe. First chart is all shots; second is just what looked like right before falling off the reg.

Tony

10 big BV 0.02 shim 1300 reg 14gr HP.JPG


10 big BV 0.02 shim 1300 reg 14gr HP 40 reg shots.JPG
 
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Shot a few groups today. Not bad for a basement throw together. Kind of windy off a front rest and the shoulder on a shaky picnic table. All at 25 yards.
14,8 gr HP. They are labeled. Looks like the 18 gr pellets have some real potential. Also, the slugs may be good with some more practice. I've seen a couple of mods for the Crosman trigger so that will be next on the hit list. I'd like to see a bit more velocity so I may experiment more with the Valken valve or if I get a new Tippman tank.

Tony

18 gr Crow Magnum number 1.JPG


14 gr HP number 1.JPG


21 gr HN slugs.JPG


14 gr HP number 2.JPG


18 gr Crow magnum number 2.JPG
 
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