[GeeTwo]

As far as the hardware, the double solenoid valves in the recent KOPs and most other doubles are designed exactly for this mode of operation. You only need to apply electricity to the solenoid for a fraction of a second (referred to as a strobe in the WPIlib) to force the change of state; air pressure then holds it in that state until you strobe the other side.

If you decide to use single solenoid valves, most of them have a "spring return" or equivalent setup; to keep them in the non-default position, you have to keep the electrons flowing.