Could be either low or high side. Just thinking maybe valve is grounded
such that high side is required. Clearly if power is isolated from valve body
low side easier, and one less error to manage.in the simple current source
shown. Eg, one would use current sink -
View attachment 163800
Obviously diode across valve coil to protect against transients prudent.
Of course MOSFET could be used, but with gate series R to decouple gate C
from OpAmp.
Regards, Dana.