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PostPosted: Sat May 04, 2019 4:58 pm 
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Location: Eastern Townships, P.Q.
After some barrel work on my Taichi-X rifle, I re-filled the tank to 20 MPa/2900 psi to test it. When I set my compressor to 3000 psi and fill, after it stops, the rifle's gauge is a hair over 20 MPa, but after cooling down it sets to exactly 20 MPa. I'm mentionning that because I had an issue with the consistency of the shots velocity. Velocity was rather inconsistent, going from too high for an under-500 fps airgun, to the mid-400s, but in an irregular way. First shot was way too high, then about 435 fps, then it rose too high again, and again, then very low, and so on. I'm sure I didn't overfilled it, and it was only the third time I filled the rifle's tank.

I took the rifle apart, first time I removed the tank from the receiver, to have a look at the regulator if possible. It was easy to unscrew the tank, and to have a direct look at the output side of the reg. First thing I noticed was the retaining C-clip (or snap-ring) was almost out of its groove. I also saw that the piston Oring was starting to extrude out of its groove. There was no way to remove the front tank cap (with the gauge) to push the regulator out, so I made a puller tool to extract it from the rear of the tank. There's a threaded hole in the piston (M3 x .5) that you can use to pull the regulator out. So I got it out without troubles, and found out that the front most Oring on the outer body was also starting to extrude out toward the rear. I completely took apart the regulator to have a look at all the components and found another small Oring in sad shape. Well I guess I'll have to rebuild the regulator.

I'd like to slightly lower the output pressure to gain more shots per fill if possible (I don't know what's the current output pressure). The Belleville washers stack is arranged in the following way: (())(())(()) + about 3mm of spacers. If I remove the spacers, will the output pressure go up or down? Would I need to re-arrange the stack a different way, for example like this: ()()()()()(). I understand that if I remove the spacers without changing the washers arrangement, there will be less ''preload''.

As for the Orings, what durometer would be recommended, 70 or 90? Also, what material? While at it, would I be better to get Urethane Orings for the sake of peace of mind? BTW, these are metric sized Orings. And where in Canada to get them?

Last question, would a bigger plenum between the regulator and valve help in shot to shot consistency? The regulator is directly butted against the receiver threaded part, so there's not much room there, I'd say no more than 5 cubic centimeters (I may be wrong though).

I'm very new to PCPs, this is actually my first one, so all infos/advices will be greatly appreciated.

Thanks in advance!


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PostPosted: Sat May 04, 2019 10:44 pm 
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Location: Eastern Townships, P.Q.
OK so I answered some of my questions with a little searching, yes google is my friend. I ordered Orings, Belleville washers and C-clips, so I hope to be able to put the rifle back together and tune it by trial and error in the coming week. Also ordered tungsten disulphide 3 micron powder to test.

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PostPosted: Sun May 05, 2019 8:18 am 
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Location: Caronport, Saskatchewan
You are a wonderfully handy guy, Airmec, but I'm ashamed this has been so much work for you. It may be a good learning experience, but you shouldn't havr to do all that to get your gun shooting acceptably.
I've got an order of the complete sets of orings and regulator parts coming for these guns as well and can send a set to you as well.
Regards,
Wes


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PostPosted: Sun May 05, 2019 9:44 am 
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Location: Eastern Townships, P.Q.
wesb2007 wrote:
You are a wonderfully handy guy, Airmec, but I'm ashamed this has been so much work for you. It may be a good learning experience, but you shouldn't havr to do all that to get your gun shooting acceptably.
I've got an order of the complete sets of orings and regulator parts coming for these guns as well and can send a set to you as well.
Regards,
Wes


Hey thanks for the kind words Wes! PM sent :wink:

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PostPosted: Sun May 05, 2019 11:30 am 
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Location: Coalmont BC
Removing some of the spacers will reduce the output pressure, and it may not take much.... My guess is that the gun is tuned quite a bit below its "plateau" velocity at the setpoint pressure, which makes it very sensitive to hammer strike.... Any slight inconsistency in that will results in larger variations in velocity.... ie shot-to-shot swings.... Lowering the setpoint pressure will help if that is the case....

Bob

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PostPosted: Sun May 05, 2019 2:47 pm 
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Location: Eastern Townships, P.Q.
rsterne wrote:
Removing some of the spacers will reduce the output pressure, and it may not take much.... My guess is that the gun is tuned quite a bit below its "plateau" velocity at the setpoint pressure, which makes it very sensitive to hammer strike.... Any slight inconsistency in that will results in larger variations in velocity.... ie shot-to-shot swings.... Lowering the setpoint pressure will help if that is the case....

Bob


Thank you Bob, very appreciated! I guess I'll have to put quite some hours of tuning time into that rifle, but at least it's rather easy to take apart.

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