[airnate]

From the FRC 2008 Pneumatics Manual:

http://www.usfirst.org/uploadedFiles...ics_Manual.pdf

SMC has provided two double solenoid valves and a single
solenoid valve. For the double solenoid valves, if you
pulse one of the solenoids to make the cylinder extend, you
must then pulse the opposite solenoid to make it retract.
Either solenoid may be left in the energized state. This is a
great valve to use to maintain position when the power is
turned off at the end of the match.