A pilot valve is the valve used to release the air from behind a diaphragm or piston valve (this airmass is called a pilot), causing it to open. It can vary in flow from a schrader valve to a 2" ball valve and above. Small diaphragm and piston valves are also sometimes used as pilot valves for bigger valves.
Blowguns are commonly used as pilot valves since they are easy to open by hand, and many have a trigger grip that fits well into the design of a gun. Ball valves are sometimes used since they have much better flow than blowguns, though they are less ergonomical.
Slide valves and three-way valves are sometimes used as pilot valves for semi-automatic cannons, in one position the chamber is filled through the pilot, in the other the pilot is exhausted and the main valve triggered.
Some problems that indicate the need for a higher flow pilot valve:
- "honking" of the valve. This loud noise indicates that your valve is oscillating open and closed.
- A 'dull' sounding launch. (note that this does not apply in the case of a chamber to barrel ratio near optimum, because there isn't much energy left over to make a loud "crack".)
- GGDT simulation indicates that your performance would be improved with a larger valve.