I harvested a PCB from a tecan cavro multichannel pump (pdf manual attached). I want to control just the solenoid 3 way valves via arduino. One PCB seems to control all 8 solenoids which are 24VDC (current I'm not so sure). From what I can see two darlington transistors control 4 valves each. My question is, how would I go about working out which of the pins to provide the 24VDC to and which pins I can switch the solenoids with?
I've attached an image of the PCB

I've attached an image of the PCB
