I am now starting to built a version 2 solenoid breakout board. While the first one works I have learnt a bit more about controlling the valves.
Added resistors in line with the diodes. The flyback diode may cause the the solenoid to release too slowly. Adding the resistor speeds up the current decay and causes the solenoid to release/close more quickly.
Using 12V 250mA solenoids with TIP121s, the resistor should not exceed 220 ohms.
Added a small bypass capacitor connected between the TIP121 emitters and the solenoid +ve terminals. The capacitor can be connected across the power in lines which is connected to the TIP121 emitters and the solenoid +V.