Increasing oil pump pressure results in finer atomization of the oil droplets.  This exposes more fuel surface area to combustion air and promotes the combustion process.

To prevent over-firing the burner, the nozzle size has to be reduced using the following chart or the included formula.  Also keep in mind that as pump pressure increases, so will the spray angle of the nozzle.  Consequently, a nozzle with a narrower spray angle may also have to be used.  

To determine fuel outputs not included on the chart, use the following formula:

New output equals (=) Rated nozzle capacity, times the square root of the New pump pressure divided by the rated pump pressure (usually 100 PSI)

For example: A 1.3 GPH fuel oil nozzle with 140 PSI pump pressure.  

New output = 1.3 X Ö140/100

                     = 1.30 X Ö1.4

                     = 1.30 X 1.18

                     = 1.54 GPH