[MrForbes]

The SMC solenoid valves seem to have built in diodes, we used them on our Promobot we built over the summer/fall and wired both ends with reversed polarity to one spike, and it switches as it should.

By reversed polarity, I mean that you connect the red wire from valve end A and the black wire from valve end B to one spike output terminal, and the black wire from A and red wire from B to the other spike output terminal.