In any water/methanol system, there are needs to route where flow goes, regulate how much volume is allowed to pass, and to time its delivery. THREE types of devices exist for these purposes: The simplest are check valves (which are spring-loaded and open passively under pump pressure). -useful for stopping leakage and drips but impossible to control independently.
Whereas, flow control solenoids are electrically actuated. Switch on 12V power to immediately open them 100%. Switch off that power for instant full closure. It's all or nothing, but actuation conditions and criteria are up to the tuner.
The most powerful devices available are USRT's "RACE valves". These are pulsed exactly like fuel injectors and can offer control as precise as EFI. (High-speed or fast acting valves in this class are sometimes abbrevated as "FAV".)