While doing consistency and other fps tests a while back we confirmed the interesting phenomena our engine has. Because the valve closes before the bb reaches the end of the barrel and in essence the fps of the bb is dependent on the valve opening time, it turns out that the valve is "self balancing" under a certain setting. What that means is that if the pressure increases slightly the valve will naturally be opened for a slightly less amount of time and vice versa. Essentially small variations in input pressure don't affect the output velocity.
Below you can see a graph of a string of 40 shots from a fixed volume non-regulated tank. The pressure drop from shot 1 to shot 40 is around 0.2 bar or 3 psi, something that a cheap regulator might produce on the output.
Note that on the graph below the valve opening time defines the fps so that the valve opens for just a fraction of the second and releases a small amount of air which then expands and pushes the bb after the valve is closed. The valve is very fast and can do this with very good precision. Because the air expands in the barrel, the shot is very quiet and the air consumption is very low.
CONCLUSION MISSING - THIS MEANS RAVEN HPA ENGINE IS...