Can the Nylon Valve or solenoid help prevent a siphon?

Yes, the nylon valves will prevent a siphon. They are normally closed valves. When set to the auto position they will only open when powered on. In most cases the Nylon Valve is installed at the entry point or the beginning of a zone. See infographics for setup on the website. https://www.instagram.com/p/COLEZzGhlfS/