At 1-4 kPa, approx. At 7-70 kPa, approx. Higher mixture pressure burners generally have longer main ports and angled retention ports around the main port to relight the flame. This includes the retention ports and dictates the maximum heat release depending on the mixture pressure, process back pressure and combustion space size. The venturi throat area regulates the primary air.
Secondary air is required to complete combustion.
Possible to elevate gas pressure and eliminate secondary air. The mixture pressure is the resulting pressure of the air and the gas. A premix burner may develop approx. 2 kPa or more allowing high heat inputs. This is the heart of a successful system.