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Author Topic: Tuning a Regulated PCP  (Read 3903 times)

rsterne

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Re: Tuning a Regulated PCP
« Reply #15 on: November 19, 2017, 04:35:06 PM »
As you lower the pressure the plateau velocity will lower as well.... Only if you are below the knee of the curve will the velocity increase with reduced pressure.... If that happens then you can assume you are somewhere on the downslope.... ie more hammer strike would increase velocity....

Bob
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charmin99

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Re: Tuning a Regulated PCP
« Reply #16 on: November 23, 2017, 03:55:26 PM »
Hello Bob,

Last question..

OK, so I have found the knee by trying various preload and dwell settings on the hammer and spring changing (costly..) and some calculation, also opened up the transfer port to optimise available setpoint pressure.

I have plotted it out and as your example it is pretty flat with a 2ft/sec variation with an amazing flat shot string of 80 then quickly falling off below at what would be the setpoint pressure.
Set point 125 bar, cylinder fill 205 bar.

The original un-regulated setup gave quite a power curve with only 38 useable shots and chronoed at 11.6 Ft/lb - 786 Ft/sec with JSB Exact 15.44

Now I have 11.0 Ft/lb 765 Ft/sec with same pellets but 80 string shots flat as a pancake...

The question, as the variation is now very good and more likely due to chrono variation I am quite happy with the result as I shoot HFT I want repeatability, however if I wanted to increase the velocity up, to say 11.6Ft/lb (785Ft/sec) and re-adjust the setpoint up, now the balance between the firing valve, striker and transfer port are set, if I just adjust the setpoint up marginally to the 11.6Ft/lb I guess I will loose a few flat shot, loose  some of the efficiency and sacrifice that for a bit higher power, is that adjustment to the setpoint now going to be a linear adjustment or close to it or would I have to start all again, which I couldnt face to be honest.

Or as you say, "enjoy what you've got.."

Thanks

Malc

  • Portsmouth, UK

rsterne

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Re: Tuning a Regulated PCP
« Reply #17 on: November 23, 2017, 04:56:09 PM »
So is the 765 fps the fastest you can get at your current setpoint, regardless of hammer preload?.... If that is the case, then yes, you need to increase the setpoint slightly to get closer to 12 FPE.... The increase in FPE should, in theory, be proportional to pressure, so if you are at 125 bar now, then 130 bar should give 11.44 FPE and 135 bar about 11.88 FPE.... Yes, you will lose some shots, both because the efficiency will be slightly less (more power) and also you will have less pressure drop from full to setpoint.... Currently you have 205-125 = 80 bar of air usable, with 135 bar you would only have 205-135 = 70 bar.... At best, your shot count should drop to 80 x 70 / 80 = 70 shots.... but probably more like 65 shots at 11.9 FPE, maybe a bit less....

or, as you say, be happy with what you have now....

Bob
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charmin99

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Re: Tuning a Regulated PCP
« Reply #18 on: November 23, 2017, 05:37:49 PM »
Thanks Bob,

Just wanted to check my thinking was correct and yes the 765 fps is the fastest.

I will have a think about it after shooting off a few more pellets (200 so far for just for this..) and see how it behaves, scope and everything set up for current setting now and as you well know this is an iterative job and personally I find you've had enough fiddling after a while... haha.



I can well live with 60 ish shots but as I said the flatness is key for me, just that over here in the UK, wind and rain on a Sunday morning shooting you can do with that last few fps...

If I do it I will let you know how it went, but can I just say many thanks, I have learnt an awful lot, yours is probably the best and most concise, relevant info I have found to date.

Many thanks

Cheers
 
 Malc
  • Portsmouth, UK