Oil-air ratio regulator is designed to provide the correct fuel/air ratio for oil-fired burners. It is used to proportion fuel flows to modulating oil burners. Combustion airflows produce a proportional pressure signal that is applied to the regulator to set the outlet oil pressure. On initial adjustment the desired oil flow rate is set to match the burner air capacities. The regulator holds this oil to air ratio at all firing rates. It has a unique balanced valve design for inlet oil pressure in the 40 psig to 100 psig range. A constant oil pressure is required at the OAR inlet.