OPD stands for Overfill Prevention Device. To verify your tank is OPD compliant, simply look for the unique triangular-shaped handwheel. Every propane grill tank manufactured in the US since October 1998 is equipped with an approved OPD valve. On April 1, 2002, it became unlawful in most states (including NC) to refill any propane tank having a capacity between 4 and 40 lbs. that is not equipped with an OPD valve.