It's factory set. Return any tank with a malfunctioning valve. Know the location of the safety relief valve, and wear adequate protection when near it. Don't deactivate the excess flow valve. Inside the tank, the valve is designed to automatically shut off any sudden gas release.
State regulations require one on every anhydrous nurse tank.
When you pick up a tank, be sure the excess flow valve has been tested recently. Always open the nurse tank valve completely to avoid restricting the excess flow valve. Don't modify the equipment by lengthening the filler hose. This increases the odds of excess flow valve failure in an emergency. Always treat applicator tubes as if they contain pressurized anhydrous, especially when unplugging them.