These units feature a 12 volt DC motor that opens or closes a rotary spool valve. Flow rates are controlled by a 12 volt signal that either increases or decreases the extent to which the valve opens.
No power is required for these flow control valves to maintain their flow settings. 12 volt signals are only applied while changing the flow rate, and then shut off to hold flow rates at their desired setting.
The valves will remain at their current flow setting in the event of a power failure or system shut down, until power is restored and a command signal is once again applied.
They are internally protected, and will automatically shut down when either full open or full closed positions are reached.