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All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"

Volume of Air Used

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QVTom:
Thanks for the explanation.  Good stuff!

Wandering of topic a bit.  I don't know much about how the metering valves on PCPs operate.  Looking at the data, it seems as the the pressure drops the valve closure delays. Is this the intended function of the valve design to try to compensate for pressure drop and maintain E or just a byproduct of less pressure to return to the closed position?

-T

 

rsterne:
It is both a result and a design feature.... In a non-Regulated PCP, the highest velocity occurs when the valve opens fully (or nearly so) against the pressure trying to close it, which is a combination of spring pressure (minor) and air pressure (major).... At higher pressures, the air is acting to prevent the valve from opening as much (and/or close it sooner).... reducing the amount of air released and limiting the velocity.... At lower pressures, the valve is still opening the maximum amount but there is less air escaping.... This produces the classic "bell curve" of velocities that we strive for....

It all comes down to a balancing act between air pressure and hammer hit.... More pressure requires more hammer hit to fully open the valve.... If you have a heavier hammer, more hammer travel, or a stronger spring (or any combination of those).... you can use a higher fill pressure.... The result will (usually) be more energy delivered to the pellet.... but fewer shots available....

The transfer port can be used to restrict the airflow and flatten the bell curve, adding more shots by supressing the peak velocity.... Conversely, opening up the porting of the valve, transfer port, and barrel port.... will usually result in more peak power but a more highly curved (and hence shorter) shot string.... Again, it's a balancing act....

Bob

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