PREMIX® Blower Mixers provide a convenient, flexible method of supply premixture for a variety of industrial burners. Air for combustion is drawn in through the ratio valve where it can be throttled. That same ratio valve includes a gas butterfly valve cross linked to the air valve. A multiple-screw cam design permits fuel flow to be matched to air flow at each firing position. This gives excellent control and allows on-ratio firing through wider operating ranges than venture mixers can provide.