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 Post subject: Tuning, re: Regulator
PostPosted: Thu Feb 02, 2017 9:25 am 
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Joined: Fri Dec 04, 2015 4:15 pm
Posts: 313
Location: Montreal, Quebec
I've got a new CZ200S "Green", probably the first and only one in Canada (it was a special order), and I'm trying to see how good a field target gun I can make out of it.

With that in mind, I ordered (and received) a better trigger, air stripper and most importantly an Altaros regulated air cylinder for it. (Getting the full cylinder with regulator, gauge and quick fill already installed was only about $40 more than just getting the parts and trying to install on my cylinder.)

So I'm trying to install everything and get the gun tuned up.

The gun itself has two adjustment points... the hammer spring tension adjustment and the venturi adjustment (not sure what the proper term for that one is). I've measured and backed out the venturi adjustment so that there shouldn't be any air restriction there.

How should the hammer spring tension be adjusted? So that the gun gives the highest velocity? Altaros suggested to me that the adjustment screw for that should be backed out so that it's flush with the housing but I'm getting 800 fps with it turned in about 3mm. I did not try (I have to do this when nobody is around at my office) last night with the screw flush, but within a full turn and a half in either direction from where it is, this position gave me the highest velocity.

Is that what I should be looking at? Velocity? Or something else?

Another thing is that there SHOULD be a set/grub screw on the side that you tighten after adjusting the hammer spring tension screw to keep it from changing. That screw is missing. (Brand new gun!!!!) And other than trying to get one from CZ in Czechoslovakia I have no idea where I might be able to find one in Canada. I've already been to three major hardware stores and could not find a screw small enough.

As far as I can tell, it's an M3 screw, maybe only about 5mm long. The hardware stores only carry M4 as the smallest. Do any of you know where I might be able to get what I need here in Canada? Ideally it would have an allen socket in the end for turning.

Thanks for any help...

Eldor

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AA S510 Xtra FAC Ultimate Sporter *CARBINE* .22
CZ200S "Green" .177
Feinwerkbau 800 Evolution Top
Air Arms S400 MPR FT .177
Steyr EVO 10
Benjamin Sheridan 397P
Stoeger X5 (non-PAL)
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PostPosted: Thu Feb 02, 2017 11:56 am 
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Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8979
Location: Coalmont BC
I tune all my regulated PCPs the same way.... I increase the hammer spring preload until I find the maximum velocity and then back it out until the velocity drops off a bit, maybe 5%.... If that isn't my target velocity, I change the regulator setpoint and repeat the process.... Here is what happens on a typical PCP....

Image

IMO you have done the correct thing by setting the venture adjustment for unrestricted flow.... Notice what happens to the efficiency on the above graph as you reduce the preload.... Going from 2 turns out (from coil bind on the spring) to 4 turns out doesn't change the velocity at all (the plateau), but you use 2/3rds of the air to get the same power.... Over the next turn, the velocity starts to decline slightly (the knee of the curve), and the air usage continues to drop.... After 5 turns out, the velocity declines (the downslope).... Although the efficiency continues to increase, as you proceed to detune the gun you will end up with another issue.... Once the pressure drops below the setpoint of the regulator, the velocity will actually INCREASE before dropping again, something you probably don't want.... A better solution would be to reduce the setpoint pressure, and tune for the knee of the curve at that lower pressure....

One other advantage of tuning to the knee of the curve (ie 4-5 turns out on the above graph).... Effectively you have tuned the gun to have its maximum velocity at just a slightly lower pressure than your setpoint.... When you reach the setpoint, you are on what would be the top of the bell-curve if the gun were unregulated, so you can take a few more shots before the velocity starts to decline noticeably.... It is not unusual to be able to extend your shot string 100-300 psi below the setpoint, gaining more useful shots per fill....

HTHs....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Feb 02, 2017 11:32 pm 
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Joined: Sat Feb 28, 2009 12:28 pm
Posts: 662
Try a hobby shop for the screw..kelly


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