Well, you didn't say what voltage the valve is, so assuming it's 12/24V, the attached circuit should do the trick.
The voltage across R2 is 150-750mV for 4-20mA current. We then add this to 12V/240 (50mV) to give 200-800mV at the positive input of the operational amplifier. The amp turrns on the transistors at its output and current passes through the valve and R3; due to the feedback to the negative input of the amp, the amp will correct the output current until the voltage across R3 is equal to the 200-800mV. As R3 is 1 ohm, this translates to 200-800mA through the valve.
View attachment 37815