Abstract: A pair of positive displacement pumps are connected in series between a liquid fuel supply tank and a burner nozzle. Mechanically linked, identical variable orifices are interposed within the supply line between the pumps and the nozzle. A first pressure regulator is connected across the supply line between the pumps and a return line leading from the nozzle back to the supply tank. A pressure sensing line for the first pressure regulator is connected to the supply line on the discharge side of the second positive displacement pump to regulate the outlet pressure of the first pump. The discharge line for one of the variable orifices leads to the burner nozzle and forms part of the supply line, while the discharge line for the other variable orifice bears a second pressure regulator and connects to the return line.