The 1/2” Brass Orifice Union is designed to be used in the pressure sensing line in the fire pump system. The union has a plate containing a 3/32” hole that provides the necessary pressure drop required by the sensing line without allowing unnecessary pump starts and false flow signals due to major pressure surges. The orifice union can only be used to flow clear water, so that no sediment or debris can block the 3/32” hole