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Tom West's Custom PC77 PumpMaster Classic Short Rifle

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I strive for 1cc per FPE I want....

June 19 2012 at 7:25 PM
rsterne  (Login rsterne)
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Response to about volume

but that's not strictly the valve volume, but the volume available for the valve to draw from easily.... eg. easier flow into the valve than out.... It's based on the concept that the larger the volume available, the higher the pressure will be at the valve seat DURING the shot cycle.... There are a large number of variables, but here is a graph showing why I use that as a goal....

[IMG][linked image][/IMG]

This graph is based on the average pressure for different sized resevoirs for the valve to draw from between a 2000 psi regulator and the valve seat, for a gun that is generating 1 FPE/CI of air used at 1 bar (ie an efficiency of 16.4 Barcc/FPE).... Cutting the volume in half (from 50 cc to 25) loses about 8% of the average pressure, whereas doubling it to 100 cc only gains about 3%.... Reducing the valve volume to 15 cc would lose about 16% of the average pressure, and if it was just 10 cc, the loss would be about 28%....

While the details of the curve will depend somewhat on the specifications of the gun, the trend should stay more or less intact.... It doesn't mean that you can't get by with a smaller valve.... but what it does mean is that as you reduce the valve (and reservoir) volume you will have to increase the starting pressure to maintain your FPE goal....


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