Mr.Wang
i would suggest that you first isolate the signal(coming from the processor) intended to switch ON the valve via an opto isolator
then hold the collector end of the opto at 24VDC through an appropriate resistor give the collector of the opto to the base resistor of say TIP 121 (this is a darlington transistor) fix your solenoid at the collector of the TIP 121 and ground the emitter also ground the emitter of the opto ,remember to isolate your +5V ground from the +24V ground and you should be able to control the solenoid