Hi.
I think this solenoid valve hasn’t a diode, because it’s nothing printed on it that shows is has. Anyway it’s easy and cheap to put one.
The 1N4001 will fit, but I used an 1N4004 of wich I have some.
The way to connect it is on the pict I posted. Here is a closer view:
As you can see, the band of the diode must point the +24v side, in order to virtually nonexist when the RUIDA opens the circuit, and do its job when closes it.
Close view of the 1N4004 and it’s band:
If you want some info about the flyweel diode you can find it here:
among tons of other info googling 