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PostPosted: Thu May 11, 2017 11:34 am 
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Joined: Mon Aug 24, 2015 4:56 pm
Posts: 462
Location: Tecumseh, Ontario in South Western Ontario
Can anyone calculate the regulator plenum volume necessary from the data below?

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PostPosted: Thu May 11, 2017 2:21 pm 
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Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8976
Location: Coalmont BC
If the above string is for an unregulated PCP, then the efficiency (FPE/CI) will apply over the whole string, from 2600 psi down to 1800, not the part you need if you are planning on regulating at 1800 - 2000 psi.... The FPE/CI over the lower pressure part of the string will be significantly lower, which means you are using more air per shot....

I try and use a plenum of 1 cc per FPE when feeding from a regulated bottle, where you don't lose bottle volume when you increase the plenum, but if you are using an in-tube regulator, obviously increasing the plenum reduces the HPA reservoir.... In that case, somewhere around 1/2 cc per FPE for the plenum will usually result in the best shot count.... In your case, that would be about 34 cc of plenum, to maintain the same FPE, but you can expect to use a regulator setpoint of about 10% higher to achieve the same FPE....

If you can currently get your 68 FPE at the bottom of your shot string (1800 psi), then a 34 cc plenum in conjunction with a 2000 psi setpoint should put you close....

Bob

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PostPosted: Thu May 11, 2017 5:01 pm 
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Joined: Mon Aug 24, 2015 4:56 pm
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Location: Tecumseh, Ontario in South Western Ontario
Thanks Bob. I tried running the shots between about 2100psi and 1800psi through Lloyds efficiency calculator to get better data on the range I want to regulate at. The efficiency was lower but not by much which must be because I'm estimating the pressure from the small manometer on the air tube :rolleyes: . I like the idea of setting the plenum volume to 34cc not only because it can be combined with a higher reg. pressure to get the higher velocity I may want but it will also work well with lower reg. pressure/velocity if necessary for better accuracy.

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PostPosted: Thu May 11, 2017 11:38 pm 
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Joined: Sat Nov 03, 2007 4:19 pm
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Location: Coalmont BC
34 cc is a decent compromise.... for an in-tube reg....

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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