double solenoid diodes?

In past years, it has been standard procedure to wire two diodes into the double solenoids, thus allowing control of both sides of the solenoid with a single spike relay. I was explaining this to someone recently, and wanted to find the documentation on it, but was unable to find it, at first. After some searching, I was able to find this information in the “Tips and Good Practices” manual…from 2006. It is NOT in the corresponding manual for 2007 or 2008.

Is this procedure still necessary? If not, why not? (Have they changed the solenoids to handle back current?) If it is, why has it been removed from the “Tips and Good Practices” manual?

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.

External diodes haven’t been necessary for several years.
See the Spike guide from 2005:

Here’s what you’re looking for See page 16. I just wired it, and it works perfectly. Why they no longer publish this diagram in the manuals is beyond me.