New spray-pattern options arrive every year — fine atomizing mists, variable hollow cones, air-assisted sheets — and yet the plain flat fan nozzles are still the default on most washing, rinsing and coating lines. Not because buyers are lazy. Because when the job is “cover this flat surface evenly,” a flat sheet is the geometry that matches the problem, and the alternatives each solve a different problem.
This guide is for the engineer or buyer who has to defend a nozzle choice, or who is staring at a header drawing and wondering whether to swap the flat fans for something newer. We will look at what “even coverage” really requires, why a flat sheet delivers it, and exactly where the alternatives beat it — so you can pick with reasons, not habit.
Throughout we will use flat fan nozzles as the working example, but the logic applies to any sheet-forming tip in the family.
What “Even Coverage” Actually Means on a Line
Even coverage is not “wet everywhere.” It is “wet to the same film thickness everywhere you care about, with no dry stripes and no double-dosed seams.” A conveyor belt wash, a panel rinse, an adhesive primer coat — all of them fail the same way when coverage is uneven: a pale streak, a thin patch, or a band that flakes later.
The surface in these jobs is flat and moving, and the target is a band of defined width. That is the key phrase: defined width. You are not trying to fill a tank or penetrate a packed bed. You are trying to paint a rectangle of liquid onto a moving plane. The nozzle that does that best is the one whose output is already a rectangle.
Why a Flat Sheet Beats a Cone for a Flat Surface
A flat fan nozzle turns liquid into a thin, flat sheet that opens into a roughly rectangular spray pattern. Fire it at a flat wall and you get a band: dense in the middle, thinning toward the two ends. That band is exactly the shape of the surface you are covering.
A hollow cone throws a round, ring-like pattern built for penetration — good for scrubbing a pipe interior or reaching into a cavity, useless for laying an even film across a belt. A full cone fills a roughly circular volume with droplets, which is what you want when you are cooling a chunk of metal or quenching, not when you are coating a sheet. A spiral nozzle does the same filling job with even more droplet density and reach. None of them produces the clean rectangular band a flat surface wants.
So flat fan nozzles win the even-coverage job not by being newer but by being shaped like the answer.
The Edge Profile Is What Makes the Band Even
The most ignored property in nozzle selection is what the pattern does at its edges. Hold a flat fan against a wall and you see the band thinning toward the ends. How it thins decides whether a row of them reads as one continuous sheet or a set of overlapping stripes.
There are two families. Tapered-edge fans fade gradually to nothing at the ends. Even-edge (sometimes called “full-edge”) fans hold near-constant density across almost the whole width and then stop abruptly. Both are legitimate; they belong in different layouts.
When nozzles sit in a row and their patterns overlap, you want tapered edges. The thin end of one sheet lands in the thick middle of its neighbour, and the two blend into a continuous line. Mount even-edge fans side by side instead and each one stops hard at its boundary, leaving a low-density seam between every pair — the repeating banding stripe operators know well. This distinction matters far more than the brand on the body, and it is the first thing to check when a line will not cover evenly.
Flat fan spray nozzles, flat spray nozzles and the plural variants you see in catalogs all describe this same sheet-forming family. The words overlap in everyday use; what separates a good choice from a bad one is the edge profile and the spray angle, not the label.
How Wide a Flat Fan Actually Covers
Coverage width follows basic geometry. On a flat surface it is:
width = 2 × standoff × tan(angle ÷ 2)
where standoff is the distance from the nozzle to the surface. At a 300 mm standoff the common angles land at roughly:
| Spray angle | Coverage at 300 mm |
|---|---|
| 15° | 80 mm |
| 25° | 130 mm |
| 40° | 220 mm |
| 65° | 380 mm |
| 80° | 500 mm |
| 110° | 860 mm |
| 145° | 1900 mm |
These assume the nozzle fires straight at a flat surface. The practical point is that widening the angle is the only way to cover more width from a fixed distance. Raising pressure does not widen the sheet — it only pushes more liquid and impact through the same angle. A wide angle spray nozzle or a wide spray nozzle earns its place when the standoff is fixed and you need to span a broad belt without adding nozzles.
For coating and rinsing duties a 65° or 80° flat fan nozzle is usually the starting point: it spreads the film wide without throwing liquid past the part. Narrow 15–25° fans concentrate energy into a thin, high-impact line that is right for cutting or descaling, wrong for an even coat.
Flat Fan vs the Alternatives
Here is the honest comparison buyers actually need:
- Hollow cone — round, hollow ring; built for impact and penetration into cavities. Wins when you must reach into a void, loses when you need a uniform band.
- Full cone — round, filled volume of droplets; wins for cooling solids, dust conditioning in a bin, or quenching. Loses on a flat moving surface where you want a sheet, not a splat.
- Spiral — high droplet density, long reach, excellent clog resistance; wins for gas scrubbing and heavy debris washing. Loses on precision film thickness because the pattern is not a clean band.
- Air-atomizing — produces a fine mist for humidification or very light coating; wins where droplet size matters more than area. Loses on simple even-coverage because it is more complex, more expensive and harder to keep uniform.
- Flat fan — the rectangular sheet; wins whenever the target is a defined-width flat band. That is most wash, rinse and coat lines.
A flat jet spray nozzle and a spray nozzle flat fan are just the same sheet-forming idea under different catalog names. Pick the family first, then the angle and edge.
The Trade-Offs You Accept When You Pick Flat Fan
Flat fans are not perfect, and pretending otherwise gets lines into trouble. The trade-offs are real:
- Narrow operating window on height. Move the header and the covered width changes proportionally. A layout proven at 300 mm standoff drifts a stripe at 200 mm.
- Pressure-sensitive flow. Flow through a fixed orifice scales with the square root of pressure, so a pressure swing changes delivered volume and can distort the pattern.
- Clog sensitivity. Small orifices pick up chips or dried coating; one partially clogged tip breaks the symmetry of the whole row.
- Overlap discipline. A flat fan only looks even when the row is spaced correctly. Bad spacing reopens seams no matter how good the tip.
None of these is a reason to avoid flat fans. They are reasons to specify them deliberately instead of by habit.
Getting the Overlap Right
Once you know the real coverage width at your standoff, you space the nozzles so their patterns overlap. For tapered-edge fans the common starting point is 40–50% of the pattern width: a nozzle covering 500 mm gets spaced about 200–250 mm from its neighbour. The thin end of each sheet then lands well inside the thick middle of the next, and the row reads as one band.
Fan spray nozzles and fan nozzles follow the same spacing math. Mixing edge types on one header — common when someone tops up a row with whatever was in the bin — is the classic source of banding, so decide the edge type up front and keep the whole row consistent.
Pressure: What It Changes and What It Doesn’t
Pressure is the lever people reach for first, so be precise about it. Flow through a fixed orifice scales with the square root of pressure. A tip rated 4 L/min at 3 bar delivers about 5.7 L/min at 6 bar, not 8. Impact rises with it, which helps cleaning but does nothing for coverage width. If your problem is a gap at the edge, opening the pump will not close it — that is angle and distance. If your problem is a coat that is too thin, more pressure helps, up to the point the pattern distorts or the pump complains.
When Flat Fan Is the Wrong Call
Be clear about the cases where you should reach for something else:
- Target is a cavity, pipe interior or packed bed → hollow cone or spiral.
- Target is a solid object you cool or quench → full cone.
- Target needs a very fine mist and droplet size is the spec → air-atomizing.
- Target is a broad flat band and you must cover it uniformly → flat fan.
A flat fan air nozzle is a different animal again: it uses flat-jet air for blow-off and drying, not liquid coverage, and it belongs in the drying zone rather than the wash zone.
Picking the Angle for the Job
Narrow angles (15–25°) throw a thin, high-impact line — right for cutting, descaling or spot cleaning, wrong for even coverage. Wide-angle fans (110–145°) lay a broad, gentle curtain that is perfect for low-pressure rinsing and dust knockdown but useless where you need to knock something off the surface. For the even-coverage job, 65–80° is the usual home.
An atlantic directional fan nozzle and similar directional variants simply aim the sheet in a fixed direction for tight spaces; the even-coverage logic is unchanged.
A Quick Selection Shortcut
Before you re-spec a header, run this down:
- Is the target a defined-width flat band? → flat fan family.
- What is the real standoff, and how wide must one nozzle cover? → pick the angle from the width formula.
- Will nozzles overlap in a row? → tapered edge, spaced at 40–50% of width.
- Single zone, no neighbour? → even edge, butt edge to edge.
- Is the fluid viscous or dirty? → upsize free passage and strain ahead of the smallest orifice.
- Only then choose the tip.
Most “the new pattern is better” swaps end up reinstalling flat fans, because the flat sheet is still the shape that matches a flat surface. If you want a second set of eyes on your header geometry, send us your duty conditions — line width, standoff, fluid and target flow are enough for us to sanity-check the angle, edge type and overlap you have specified, and to point you to the right flat fan nozzles for the job.