[jspatz1]

Another way to describe single vs. double solenoid: Single solenoid valves are actuated by the solenoid, but are spring loaded to return to the normal state when the solenoid is off. So they will actuate only while the solenoid is energized, and will return to normal state when power is off. A double solenoid is solenoid-driven in both directions, and has no spring. Either solenoid is energized to actuate the valve into either state. The valve will remain in the last state, even without power, until it is electrically or manually changed.