Tell your dad this: Try activating the valve electronically, but keep the valve activated. Blow into the input end. Air will come out the other end, but slowly, and it will be hard to blow into the valve. This is because the human lungs are only capable of about 2 psig of pressure. The valve needs about 3 psig or so difference between the pilot area and the chamber for the diaphragm to lift, so the air can only exit through the bleed hole, which is ordinarily covered by the solenoid. The solenoid bleeds off some of the air to make this difference (At high pressures, the difference is enough). However, the bleed is slow and constricted. The blowgun does the same thing as the solenoid, but it bleeds a lot more air, therefore triggering the diaphragm lift MUCH faster (Around 10x faster!).
The most important part is that once the diaphragm lifts, it has a larger area for air to flow than either the blowgun or the solenoid bleed port. Unless your blowgun has a hole at the end that is about 2 inches wide, (doubtful) a huge portion of the air will take the path of least resistance and flow past the open diaphragm and into the barrel. This is the part that your dad seems to be missing.
Hope I was helpful! My dad also thought my valve would be a total loss, until I fired a demonstration shot!
This was my first modified valve, and I can definitively say that it was well worth the money! If you'd like to know more about this stuff, read up on compressible flow, and fluidics.
