Major Collins wrote:what exactly do you mean tension, like the spring still wants to move forward after the hammer is resting at the valve stem
He means when the hammer is at rest, the spring is still compressed so that it will hold that valve open. This is a pilot, not a main valve, so you want the valve to stay open in order for the piston to pilot properly.
and why do I want the hammer at rest to hold the valve open ?
wont that mean when I release the hammer when it hit the stem it will hold the valve open and the stem wont be able to reset - in return just dump all the air ?
Once again that is the point here, since this is a pilot and not a main valve.