Single vs double solenoid valve operation
Since the question about operation has come up within a different thread (about wiring them), hopefully the following explains how the valves operate, and the impact on the cylinder....
A single solenoid valve has one solenoid, and shifts when voltage is supplied to that solenoid. When voltage is removed, it shifts back to a "home" position.
This means that a cylinder has a home position when hooked up to a single solenoid valve, and is in that home position when no volatage is supplied. Note that while many think of the home position as being cylinder retracted, if you switch the tubes to the opposite ends of the cylinder, the home position can be extended.
So, at the end of the game when power is cut, if voltage was being supplied to the solenoid, the cylinder will return to it's home position. If no voltage was being supplied when the game ends, the cylinder will stay in the position it was working in. Depending upon what the cylinder was doing, this may or may not be desired.
A double solenoid has two solenoids, and when voltage is supplied to one (and not the other) the valve shifts. Note that if voltage is supplied to both solenoids at the same time, the valve will stay in the position is was in (i.e. it won't shift since the solenoids will be working against each other). This is typically not desired, so make sure you remove voltage from one side when supplying it to the other.
If no voltage is supplied to either solenoid, the result will be the same as if voltage is supplied to both, in that the valve will stay in the position is was in.
What this means is that the cylinder has no home position, so when power is cut, the valve will stay where it was at that time, and the cylinder will continue to do work in the direction is was working in. Again, depending upon what the cylinder was doing, this may or may not be desired.
Hope this helps...