Fluid pressure in a variable volume whirl chamber exerts a force that posons a spring biased piston. The positioning of the piston determines the amount of fuel oil supplied to a ship's boiler by an arrangement of ports in a whirl chamber cartridge. The cartridge provides an enclosure for the whirl chamber, a piston and a biasing spring. The fuel is delivered axially along the outside of the cartridge through the ports to the whirl chamber and out an orifice located at the forward end of the whirl chamber.
