by B.B. Pelletier
This final blog of 2008 was inspired by several questions from reader Kevin but also from other readers who are now owners of precharged pneumatic (PCP) airguns. I’ve written these things before, but perhaps never put them in the same order as I will today.
A PCP valve operates best between a certain high and low pressure point. That is to say the valve will open and remain open long enough to pass air from the reservoir to power a pellet to more or less the same velocity. When the reservoir pressure is high, it acts on the valve to close it faster, but the air that passes through the valve when the gun fires is under a lot of pressure. As you continue to shoot and the reservoir pressure drops, it acts with less force and less quickly on the valve to close it, so the valve remains open slightly longer. The air that passes through the valve before it closes is not pressurized as high; but since the valve remains open slightly longer, it delivers similar acceleration to the pellet. The result is that the pellet stays at the same velocity, more or less, throughout a number of shots.