Section 02.03.03.685 - VACUUM RELIEF VALVE OR COMBINATION AIR AND VACUUM RELIEF VALVE01.Location. Will be located on top of the horizontal irrigation pipeline on the upstream side of the check valve. (3-15-22)02.Orifice Size. Have have a total (individually or combined) orifice size of at least three-fourths (¾) inch diameter for a four (4) inch pipe, a one (1) inch diameter for a five (5) to eight (8) inch pipe, a two (2) inch diameter for a nine (9) to eighteen (18) inch pipe, and a three (3) inch diameter for a nineteen (19) inch and greater pipe. (3-15-22)Idaho Admin. Code r. 02.03.03.685