A liquid fuel nozzle is the smallest component in the burner and decides whether the flame is clean. It forces oil through a swirl chamber at pressure and shears the stream into droplets, so change the geometry of that swirl and you have changed the flame, whatever the pump and air train do.
Angle decides where the flame sits
Spray angle is the included angle of the cone leaving the nozzle, and it exists to match the flame to the chamber. A narrow cone concentrates energy along its axis, suiting a chamber where the flame should reach deep without washing the walls. A wide cone spreads that energy over a larger area, which is what a shallow hearth or low radiant tube needs to avoid a hot spot underneath.
Matching matters more than the nominal figure. A cone too narrow impinges on a wall or refractory face, and the flame root travels along that surface until it stabilises or lights back. A cone too wide leaves the chamber corners cool, so the load sees a lower temperature at the edges than the control sensor reads at the centre. Both present as uneven work, not as a burner fault.
Pattern is a different choice from angle
Angle describes the cone shape; pattern describes what happens inside it. A hollow cone has air at the centre and fuel at the edge, because the swirl pulls the centre into a low-pressure core. A full cone distributes fuel across the section with no central void. A flat pattern is used where the burner fires along a surface rather than into a volume.
The consequence shows up in the air. A hollow cone mixes well with the air it entrains, which is why it suits most chamber work. A full cone carries more velocity forward and needs careful air alignment to avoid a long luminous flame. Where a burner was designed for one pattern, fitting the other without changing the air path produces a flame no amount of ratio adjustment will correct.
Pressure and rating have to agree with the pump
A nozzle rating is a flow figure valid at a stated pressure, and that has to be the pressure the oil pump delivers at that flow. The common error is not a wrong nozzle so much as a right nozzle at the wrong pressure. A rating above what the pump can deliver means the burner never reaches its intended input; a rating below lets it reach temperature on a starved flame, which shows up as carbon monoxide rather than an obvious fault.
Because the two are coupled, a nozzle change is a pump decision as much as a nozzle decision. The viscosity of the fuel moves the pressure the pump must hold to get that flow, so the same nozzle behaves differently on a thinner oil than a heavier one. Record the nozzle rating, pump setting and oil together, or the next person to service the appliance works from one number out of three.
Single or multiple nozzles
A single nozzle has one swirl chamber and one droplet size distribution. Multiple nozzles divide the flow, each smaller and positioned differently, which is how a burner gets a wide flame without widening the chamber. The trade is mechanical: every extra nozzle is another orifice to block and another part to order, and a block reassembled with one nozzle swapped gives a lopsided flame that mimics a chamber problem.
What wear does to a nozzle
Erosion shows up in stages. A nozzle running on dirty fuel or through a failed filter develops a groove in the swirl chamber, weakening the swirl. That lengthens the flame and drops the pressure at which the nozzle holds its rating. The same wear can let the seating face leak, so oil escapes upstream of the orifice and the pump sees flow it cannot account for.
Neither symptom is obvious at the burner. A gradual lengthening of the flame gets written off as a fuel supply variation, and an unexplained pump pressure drop gets chased in the filter. A spare oil nozzle on the shelf is cheap against either investigation, and the test that separates them is to fit a known-good nozzle of the same rating.
Frequently asked questions
What does the spray angle number on a nozzle actually mean?
It is the included angle of the cone leaving the orifice, measured at a stated distance from the tip. It gives you the geometry, not where the flame sits, because the flame also depends on swirl, pressure and air direction. Use it to match to the chamber, then confirm on the appliance.
Can I fit a higher rated nozzle on an existing burner?
Only if the pump can deliver the pressure that rating assumes. A nozzle sized above the pump's capability never reaches its rated flow, and the burner sits below its intended input at any pressure the pump can produce. Where the input has to go up, the oil circuit, pump and often the air side all move with it. That is a burner decision rather than a nozzle swap.
Why does a worn nozzle give a longer flame?
Erosion in the swirl chamber weakens the rotation, so the oil leaves with less tangential velocity and less internal mixing. The result is a less atomised, more elongated stream that behaves partly like a free jet, and the flame grows longer. Fitting a known-good nozzle of the same rating is the quickest way to confirm it.
How often should nozzles be inspected?
The interval is set by the condition of the oil, so sites on heavier or contaminated fuel inspect more often than those on clean light oil. Inspect once the filter downstream of the tank has passed what it was rated to catch, when material likely to erode a swirl chamber is through. Our light oil burner range covers the types where it differs.
Does nozzle size affect the turndown of the burner?
It does, indirectly. The low end of a range is set by how well the flame holds together as fuel flow falls, and a nozzle that atomises well at full flow may produce a poor spray at a fraction of it. That is why two burners of the same size with different nozzle ratings behave differently at low fire. The turndown notes cover how that is established.
What has to be checked after changing a nozzle?
That the replacement is the same rating and pattern as the one removed, and the same angle if the chamber is unchanged. Then re-establish the oil pressure, re-check the ratio and walk the burner across its range, because a nozzle change alters both the spray and the air the flame needs. Our parts cross-reference notes cover keeping that record usable.
Request a quote
Zhongli Weiye supplies nozzles, nozzle blocks and oil circuit components matched to the burner installed, and matches a replacement to the rating and pattern recorded for the appliance. Send the burner model, the nozzle marking if legible and the oil fired, and the recommendation comes back with the parts that fit.
Related products
The parts and product families referenced in this guide:
- oil nozzle spray pattern chart
- oil pump supply pressure check
- oil heating fuel handling
- light oil burner families
- oil burner pump replacement
This guide covers Burner Nozzle Selection: Angle, Pattern and Pressure. For the exact part that fits your duty, send us the model plate photo and we confirm availability, lead time and a matched quotation.