MUSICAL WATER Fountains solenoid valves rather than pneumatic cylinders. The pressure for the expulsion of water is computed beforehand and this value is translated in terms of current and is fed to the solenoid through an electronic circuit from the computer. The current through the solenoid determines the magnitude of the valve opening. This might be thought of being analogous to a graphic equalizer on your music system. The opening and closing of valves ensure the pressure inside the canons and is tremendously rapid. The current is, usually dependent on the frequency of the note being played.