What is the typical pressure on a residential oil burner?

Answer 1

For most units built before 1970 the pump pressure for an oil burner should be set at 100psi, but for more modern flame retention burners pump pressures of 130 to 150 psi at the oil nozzle are commonly specified. Searching for setup instructions for the specific make and model of the furnace or boiler as a "package" will often yield more specific and correctly optimized information than searching for information about the burner.

Anyone interested in this question should know that the oil pump on an oil burner is adjustable: for residential burner pumps generally between 100psi and 200psi. There is usually a 1/8" NPT gauge port suitable for a gauge that reads at least 150 PSI full scale. Pumps usually incorporate a spring-loaded stop valve so that, as the burner shuts off and the motor (that turns the pump and the blower) slows down, the flow of oil to the nozzle is blocked-off when the pump pressure falls below 80psi.

At lower pressures the oil droplets are larger and travelliing slower; at higher pressures they are smaller and travelling faster. All other things being equal, smaller droplets are preferred because the ideal is fully vaporised fuel; but all things aren't equal... A compact high-temperature flame is ideal, but high velocity droplets expand the flame: as the flame begins to separate from the burner head if will pulsate noticably, and the draft regulator may begin to swing rapidly. The modern flame retention burner uses a helically-swirling pattern of air from a higher pressure blower to gain the advantage of a smaller droplet size while keeping the flame compact.

As it is most efficient if the flame size is made optimal for the boiler's or furnace's firebox, so also there is an optimal fire-size and firing rate for a given boiler. However, since there is significant heat-loss up the chimney during the each "off" phase, it follows that, given a particular boiler already in place, seasonal oil consumption is usually minimized by chosing a firing rate that is almost continuous in the coldest weather. To optimize efficiency choose a nozzle and oil pressure so that, when air is correctly adjusted for peak burning efficiency, the fire fills the firebox without actually impinging on the walls.