Which sprinkler valve model to buy?
Not to sound rude or demeaning but anyone who doesn't possess the mechanical aptitude to be inventive enough to figure out how spudgun's work and how to build them, probably shouldn't... If you don't understand the theory behind the mechanics then you are a danger to yourself and anyone else around you while handling your spudgun... Finding a safer hobby to take up might be the best course of action in such a case... Do more than ample research so you know what you're doing rather than simply taking someone else's advice... It's part of the process...