Driving solenoid valve using LM358 as comparator and ULN2003
You can parallel the drivers on a single chip and expect them to share current reasonably well, since they are matched (being all created with the same process). 

Assuming you are using the DIP package, here is what is acceptable: 



It looks like even with 7 outputs in parallel it's a bit marginal at 85°C ,maximum Ta. It would be worse for an SMT package. I suggest using a MOSFET and flyback diode.