Powering a solenoid valve with a relay and no external power source
A relay is just a switch.  You have to provide power to the solenoid through the relay.

You can wire the solenoid to be powered by the 12V from the relay board.


Connect the red wire from the solenoid to the + pole of the terminal block beside the DC plug.
Connect the black wire from the solenoid to the NO connection of the relay terminal block.
Connect the COM terminal of the same relay terminal block to the - pole of the terminal block by the DC plug.


When you send a signal to the relay board, it will supply power from the DC powersupply to the solenoid through the relay.




No schematic because the site's schematic software doesn't work on phones.
The DC terminal block and the DC plug appear to simply be in parallel.  If they are connected with a diode "OR," then this suggestion won't work.  I don't see any diodes, though, so it should be fine.