This is the simplest and oldest design of burner. Atomisation of the fuel is achieved by forcing the fuel under pressure through an orifice at the end of the burner, the pressure energy in the fuel is converted to velocity. Spin is given to the fuel prior to the orifice imparting centrifugal force on the spray of fuel causing it to atomise. The disadvantage of this burner is its low **Turn-Down** ratio (in the region of 3.5). The advantage is that it does not require any assistance other than supplying the fuel at the correct pressure. Due to this it is still seen even on larger plant were it is used as a first start or emergency burner. Another disadvantage over assisted atomization burners is the lack of cooling from stam or air means the burner must be removed when not in use from lit boilers to prevent carbonizing in the tube.