Glossary
Spill-back atomizer
Definition
Pressure atomizer in which the fuel that is not sprayed returns to the tank through a spill-back line; regulating that return modulates the output.
A spill-back atomizer (also written spillback atomizer, German Rücklaufdüse) is a pressure atomizer with a second fuel line. The pump delivers more fuel than the nozzle actually sprays; the surplus leaves the nozzle through the spill-back connection and returns to the tank. The pressure at the nozzle inlet therefore stays almost constant while the quantity that is atomized is set by the return-flow valve.
Because the spray is produced by the same swirl chamber at a nearly constant pressure, the spray angle and the spray pattern stay stable over the whole modulation band. That is the reason a spill-back atomizer reaches a turn-down of 1:3 – 1:5 where a plain simplex atomizer is limited to roughly 1:2. The price for that is an extra fuel line and a return-flow regulator in the oil train.
Fluid Control Instruments Ltd builds the spill-back atomizer in three sizes — TYPE 9 (8 – 250 kg/h), TYPE 12 (20 – 750 kg/h) and TYPE 32 (60 – 2250 kg/h) — with or without a shut-off needle, and adapts the spray pattern to the character of the combustion head.