Flat Fan Nozzles: Angle, Coverage and the Even-Strip Problem

A flat fan nozzle is the most-used spray shape in industry because it makes an even band, a strip of uniform liquid, not a cone, not a cloud. That evenness is what washing, coating, marking and fertilising strips depend on. The whole game is angle (band width), orifice (flow), and header layout (whether the bands overlap into a uniform sheet or stack into a heavy centre).

The Selection Framework: Three Numbers

Every flat-fan duty reduces to three numbers. Write them down before you touch a catalogue:

1. Band width needed: how wide must the strip be at the work distance? This picks the spray angle and the standoff.
2. Flow per unit width: how much liquid per metre of band? This picks the orifice and the pressure.
3. Uniformity requirement: is the coat graded (even across the band) or just wet? This decides whether you need an even-edge tip and how the header is laid out.

A flat fan chosen without these three is a guess with a part number. With them, the selection is arithmetic.

Reference Flow Table (Clean Water)

Our standard flat-fan line, flow quoted at 3 bar:

Model	Spray angle	Flow @ 3 bar	Free passage	Edge type	Connection	Material
BJ-FF15	15°	1.2–4 L/min	0.8 mm	Even	1/8“–1/4“	303 / 316L
BJ-FF25	25°	1.6–8 L/min	1.0 mm	Tapered	1/8“–1/4“	303 / 316L
BJ-FF40	40°	2.4–16 L/min	1.2 mm	Tapered	1/4“–3/8“	316L
BJ-FF65	65°	4–30 L/min	1.6 mm	Tapered	1/4“–1/2“	316L
BJ-FF80	80°	6–45 L/min	2.0 mm	Tapered	3/8“–1/2“	316L / PP
BJ-FF110	110°	8–60 L/min	2.4 mm	Tapered	1/2“–3/4“	316L / PP
BJ-FF145	145°	12–90 L/min	3.0 mm	Even	1/2“–1“	316L / PP
BJ-FFHP	15°–40°	2–20 L/min	1.0 mm	Even	1/4“–1/2“	Hardened SS

Flows are at 3 bar with clean water. Viscous or hot fluid shifts the numbers. Send your duty for a real sizing.

The full flat-fan line is on the flat-fan products page: per-tip angle, flow, edge type and connection.

Spray Angle: The Band Width

The fan angle (15°–150°) sets how wide the band opens at a given distance:

• 15–40°: narrow, high-impact band for cutting, marking, jetting.
• 65–80°: general-purpose, the default for most spraying.
• 110–150°: wide, thin band for flooding a near surface.

At a fixed distance the band width scales with the tangent of half the angle. A 15° tip makes a pencil; a 150° tip makes a wide sheet. The angle is chosen by the surface, the distance by the fan rating.

Flow and the Orifice

Flow at a given pressure is set by the orifice. Flat-fan tips are coded by angle and orifice (e.g. a “TT” series with angle and a flow number). The same angle at a larger orifice flows more; the same orifice at higher pressure flows more (roughly with √pressure). The trap is again total flow: a spray bar of 20 tips at 2 L/min each is 40 L/min, and the pump must hold pressure at that total.

Even Coverage: The Real Problem

A single flat fan is even across its band. But bands from a header must overlap to make a uniform sheet. Two failures:

• Gaps → tips too far apart, bands don’t meet. Dry lanes.
• Heavy centre → tips too close or angled wrong, bands stack. Flooded strip.

The fix is layout, not a different tip: space tips at ~60–80% of the band width at the work distance, alternate their aim if needed, and hold pressure so every band is the same width. A header that sags in pressure gets uneven bands → stripes.

Hydraulic vs Air-Assisted Flat Fan

A plain hydraulic flat fan needs only pressure. When the finish must be uniform on a delicate surface (coating, dosing), an air-assist flat fan adds a low-volume air shroud that flattens and controls the band better. Cost is the air supply; benefit is control hydraulic cannot reach. For most washdown and marking, hydraulic is enough.

Material and Service

• 303 / 316L stainless for water-based and mild chemistry, standard.
• PP / PVDF for acids and oxidisers; PVDF for heat.
• PTFE-lined for broad resistance.
• Ceramic or carbide orifice in abrasive slurries (filled coatings, pigments). The orifice wears first.

For cleaning and marking, 316L; for pigmented or abrasive fluids, ceramic-insert tips.

Troubleshooting

1. Stripes (light/dark bands) → pressure sag or uneven tip spacing. Hold pressure, check spacing.
2. Heavy centre → tips too close or angled in. Widen spacing, aim outward.
3. Clogging → orifice too small for the fluid. Filter the supply (100–200 mesh) or step up the orifice.
4. Wrong angle for the surface → narrow tip on a wide part leaves edges dry. Widen the angle.

How We Compare to the Catalogue Brands

The major spray catalogues (Spraying Systems, Lechler, BETE) publish flat-fan lines with documented angle, flow and band uniformity. Our flat fans track the same coding and physics. A 110° tip at 3 bar flows the same band their equivalents do. What a buyer weighs is spare-tip stock, ceramic option, and lead time, not the angle math. We publish per-tip flow and angle so you lay out the header against the same numbers.

Industry Applications: Where Flat Fans Earn Their Keep

• Washdown and pre-rinse: a 80–110° flat fan on a header floods a conveyor or wall with an even band; no dry lanes, no stripes.
• Coating and glazing: an even-edge tip lays a uniform coat on a web or board; the graded band is the whole product.
• Marking and striping: a narrow 15–25° tip paints a line; the even edge keeps the stripe crisp.
• Cooling: a wide band of water on a hot sheet; even coverage prevents hot spots and distortion.
• Dust suppression: a wide-angle flat fan blankets a transfer point; the band catches dust before it rises.
• Fertiliser and chemical application: a graded flat fan spreads the product evenly across the swath; stripes mean wasted chemical and uneven crop.

Each application is the same three numbers with a different answer set.

Worked Example

You coat a 1 m wide conveyor belt with a 3-tip header, water-based coating, 2 L/min per tip at 3 bar.

1. Angle → 80° tip at 30 cm gives ~0.4 m band. Three tips cover 1 m with overlap.
2. Flow → 3 × 2 = 6 L/min; pump holds 3 bar at that total. Good.
3. Spacing → tips 33 cm apart, band 40 cm → ~80% overlap, uniform.
4. Material → water-based → 316L.

Even coat, no stripes, no flood.

FAQ: Flat Fan Questions We Actually Get

Q: Why is my band heavy in the middle? A: Tips too close together or angled inward. The bands stack. Widen the spacing or aim the tips outward so the bands just overlap.

Q: Why do I see light and dark stripes? A: Pressure sag. The pump can’t hold rated at total flow, so the end tips make narrower bands. Size the pump to aggregate flow, or use a pressure-compensating line.

Q: Even-edge or tapered-edge tip? A: Even edge for a graded coat (coating, marking). Tapered edge for washdown where a little falloff at the edges is fine and the tip is cheaper.

Q: Can I run a flat fan on recycled water? A: Yes, if the free passage exceeds your largest particle and you filter. A 2.4 mm free passage passes more than a 0.8 mm one; match the orifice to the water.

Q: How close should the tip be to the work? A: At the rated standoff. The angle rating is measured at a fixed distance. Wander from it and the band widens or narrows, changing coverage and impact.

Selection Checklist (Print This)

• Band width needed measured at the work distance
• Spray angle chosen: narrow for lines, wide for floods
• Flow per metre summed; pump holds rated pressure at that total
• Edge type chosen: even for graded, tapered for washdown
• Free passage sized above the largest suspended particle
• Tips spaced at ~60–80% of band width for overlap
• Material matched to chemistry + temperature with margin
• Spare tips on the shelf. Flat fans wear at the orifice

The Physics of the Even Band

A flat fan works by shaping a sheet of liquid and letting it break into drops. Three physical facts drive every design:

• The band is thinnest at the centre and thickest at the edges: the liquid volume is spread over a wider arc in the middle. A well-designed tip compensates with an even distribution; a cheap one doesn’t, and you get a heavy centre.
• Impact falls with distance squared: double the standoff, quarter the force at the surface. The angle sets the width, the distance sets the impact, and they fight: hold the distance the tip was rated for.
• The free passage sets the clog ceiling: a 2.4 mm passage passes grit that sieges a 0.8 mm one. The orifice is the choke point; match it to the water, not to the spray.

That is why the same “angle” on two brands can spray differently: the internal distribution, not the angle number, decides the band’s evenness.

Header Design: Making Many Bands One Sheet

A single flat fan covers a strip; a header of tips covers a sheet. The layout is where uniformity is won or lost:

• Spacing: tips at ~60–80% of the band width at the work distance, so the bands overlap into one even sheet.
• Stagger and aim: alternate the tip aim slightly outboard on wide headers to flatten the combined profile.
• Pressure across the header: the last tip must see the same pressure as the first. A loop feed or a properly sized header beats a dead-end line.
• Tip-to-work distance: every tip at the same distance, or the band widths differ and stripes appear.

A perfect tip on a bad header still stripes. The header is as much the system as the nozzle.

Maintenance: What Kills a Flat Fan

• Orifice erosion: the hole enlarges, flow creeps up, the band widens and thins. In abrasive water, check every season; the flow test catches it.
• Deflection-edge fouling: a coated edge sprays lopsided. Clean the edge with a brush or solvent; don’t replace the body.
• Scale and deposits: hard water scales the orifice; the band narrows and distorts. Descale or feed softened water.
• Chemical attack: the wrong material for the fluid pits the body. Match material to chemistry with margin.

A flat fan is a wear part. Replace on inspection. A worn tip costs more in process drift than it does to replace.

Worked Sizing: A 2 m Washdown Header

A 2 m wide conveyor washdown, water-based, needs an even band at 3 bar, pump rated 12 bar at 120 L/min.

1. Band width: 2 m in one pass needs tips that together cover 2 m with overlap. Five BJ-FF65 tips (65°, ~0.5 m band at 40 cm) at 40 cm spacing covers 2 m with ~20% overlap.
2. Flow: BJ-FF65 at ~8 L/min each × 5 = 40 L/min total. The pump holds 120 at 12 bar, huge headroom. Good.
3. Edge: washdown → tapered edge is fine (no grading needed).
4. Material: water-based → 316L.
5. Layout: tips 40 cm apart, 40 cm above the belt, loop-fed so the last tip sees 3 bar.

Answer: 5 × BJ-FF65, 316L, 40 cm spacing, 40 L/min total. Even band, no stripes.

Material Selection Table

Material	Max temp	Chemistry	Best for
303 SS	~300 °C	Mild	General service, cheap
316L SS	~300 °C	Process water, mild corrosives	The default
PP	~80 °C	Acids, alkalis	Light chemical duty
PVDF	~140 °C	Oxidisers, halogens	Aggressive chemistry
PTFE-lined	~200 °C	Broad	Worst-case chemistry
Hardened SS	~300 °C	Abrasives, high wear	Orifice in slurry duty

Match the material to the fluid first, then the temperature with margin. A 316L tip on a bleach line fails; a PP tip on a hot washdown melts.

The Five Mistakes to Avoid

1. Picking angle by eye: measure the band you need, then choose the angle for that width at your standoff.
2. Ignoring total flow: a 20-tip header at 8 L/min each is 160 L/min; the pump must hold rated pressure at that total, not at one tip.
3. Spacing tips too far: bands gap and you get dry lanes. Overlap at 60–80% of band width.
4. Wrong edge type: a tapered tip on a graded coat gives edge falloff. Even edge for grading.
5. Skipping the filter: a 0.8 mm free passage sieges on any grit. Filter the supply.

Every one is a system error. Size the three numbers and the five mistakes disappear.

Air-Assisted Flat Fans: When the Band Needs Help

A plain hydraulic flat fan relies on pressure alone. When the finish must be uniform on a delicate surface, coating, glazing, dosing, an air-assisted flat fan adds a low-volume air shroud:

• The air flattens the band: the shroud controls the fan’s shape and reduces edge curling, giving a crisper, more even strip.
• Finer drops at lower liquid pressure: air does part of the atomisation, so the liquid line can run lower and the drops stay fine.
• The cost is air: a compressor and a regulated feed per tip. For a single tip it is cheap; for a 20-tip header the air bill adds up.

The rule: hydraulic flat fan for washdown and marking (simplicity wins); air-assisted when the band’s uniformity is the product (coating, dosing).

Droplet Size and the Band

Flat fans make drops in a wide band: from fine mist at the edges to larger drops in the core. Two consequences:

• For washing, the droplet size barely matters; coverage and impact do. Don’t pay for fine atomisation you don’t need.
• For coating and marking, the drop must be fine enough to level on the surface without runs. If the finish shows orange peel or runs, the pressure is too low (coarse drops) or the standoff too short.

The flat fan’s droplet distribution is a side effect of its design, not a spec you tune independently. Tune pressure for the finish; choose angle for the width.

What to Send a Supplier for a Quote

1. Band width at a known distance: the strip you must cover and the standoff you can hold.
2. Flow per metre: litres per minute per metre of band, or the total header flow and tip count.
3. Fluid and temperature: chemistry and hot/cold; both change the material and the flow.
4. Uniformity requirement: graded coat (even edge) or washdown (tapered is fine).

With those four, the quote comes back with a model and a header layout. Without them, every supplier picks blind.

The One-Paragraph Summary

A flat fan makes an even band: measure the width you must cover, pick the angle for that width at your standoff, size the orifice for the flow your pump holds, space the tips for overlap, and match the material to the chemistry. Get the three numbers right and the strip is even. Get them wrong and you stripe, flood or miss.

When the Flat Fan Is the Wrong Tool

Sometimes the answer is a different pattern entirely: a solid stream for a jet that must reach (the fan sheds its coherence in a metre or two), a full-cone spiral for dirty water (the fan’s edge clogs), or a misting tip for air conditioning (the fan wets, it doesn’t evaporate). The flat fan owns the even strip; outside that job, the tool changes.

Band Width at a Glance

Quick reference for the band a flat fan makes at a typical 40 cm standoff:

Angle	Band at 40 cm	Use
15°	~10 cm	Marking, lines
25°	~18 cm	Stripes, narrow wash
40°	~29 cm	General spray
65°	~51 cm	Washdown headers
80°	~67 cm	Wide flood
110°	~114 cm	Very wide coverage

The width scales with the tangent of half the angle. These are the clean-water numbers at rated distance. Hold the standoff and the table holds.

Even Edge vs Tapered Edge: The Fine Print

The two edge types exist because real bands fall off at the edges:

• Tapered edge: the band thins smoothly at both edges. Cheaper, fine for washdown where the strips overlap anyway. The majority of industrial flat fans are tapered.
• Even edge: the tip is shaped to hold the same flow right to the edge of the band. Pricier, and the one you want for grading, coating and marking where a fallen-off edge shows as a stripe.

If you don’t know which you need, you need tapered. It is the default and it is cheaper. Step to even edge only when the coat is graded and the edge matters.

Bottom Line

A flat fan nozzle makes an even band. Angle sets the width, orifice sets the flow, header layout sets the uniformity. Pick the angle for the surface, space tips for overlap, hold the pressure, and the strip is even. The heavy-centre/light-edge problem is never the tip, it is the layout.

Reading the Part Number: The 8005 Code Explained

The single most useful skill for buying flat fan nozzles is reading the part number, because the industry’s dominant numbering system encodes the two numbers that matter, spray angle and flow rate, directly into the code. Spraying Systems Company’s convention is the reference most suppliers follow, and understanding it lets you decode a nozzle from a photo or a spare-parts list.

The format is: angle + flow.

An 8005 nozzle means:

• 80 = 80° spray angle
• 05 = 0.5 US gallons per minute at 40 psi rated pressure

An 11002 nozzle means 110° spray angle at 0.2 gpm / 40 psi. The flow digits are a shorthand: 02 = 0.2, 05 = 0.5, 08 = 0.8, 10 = 1.0, 20 = 2.0, 40 = 4.0 gpm.

Three practical consequences fall out of this:

1. Angle and flow are independent. You can pick an 80° nozzle at 0.5 gpm or an 80° nozzle at 4.0 gpm, same angle, completely different duty. The code tells you both at once.
2. The rated pressure matters. 40 psi is the reference point. Run the same nozzle at 80 psi and the flow rises by roughly √2 (about 41% more), and the spray angle narrows slightly.
3. Conversion is simple. US gpm at 40 psi × 3.22 ≈ litres/min at 2 bar, a useful bridge when comparing a US-sourced part against a metric catalogue.

When you send a supplier a flat fan enquiry, quoting the code style (80° / 0.5 gpm @ 40 psi) is the fastest way to get a comparable quote, because every manufacturer maps their own series onto the same angle-and-flow language.

Parabolic vs Even Distribution: The Two Edge Behaviours

Flat fan nozzles divide into two distribution philosophies, and the difference decides whether the band is a single-nozzle wash or part of a multi-nozzle header.

Parabolic (tapered-edge) distribution: the classic flat fan. The spray is brightest in the centre and falls off toward the edges. Used alone, a parabolic nozzle leaves a lighter band at each edge; but when nozzles are overlapped in a header, the tapered edges add up to a uniform combined band. This is why parabolic flat fans dominate multi-nozzle headers: overlap is built into the design.

Even (uniform) distribution: the spray delivers the same liquid load across the full band width, edge to edge. Used alone or in pairs, an even nozzle covers a strip uniformly without relying on neighbour overlap. Even flat fans are the right choice for single-nozzle washdowns, banding in agriculture, and coating lines where one nozzle carries the whole width.

The practical rule: overlap parabolic fans, don’t overlap even fans. Two even nozzles overlapped create a heavy double-strength stripe down the overlap line; two parabolic fans at the right spacing merge into a flat combined profile. Most header design failures trace back to mixing the two types or overlapping even fans.

Header Overlap Rules: Spacing That Doesn’t Streak

When building a multi-nozzle header, the spacing and angle-offset rules come from the nozzle manufacturers’ planning tables and are consistent across Lechler, Spraying Systems and Fluid Products literature:

• Angle offset 5–15°. Tilt alternating nozzles 5–15° off the perpendicular so adjacent spray sheets do not collide in mid-air. Colliding sheets rob each other of energy and create a disturbed, uneven band.
• Parabolic fans: overlap to a flat profile. Space the nozzles so the combined edge-to-edge coverage is even. As a starting point, the target spacing is the one that gives roughly 50% coverage overlap of each nozzle’s band at the working height, then check with a pattern test.
• Even fans: 0% or 50% overlap only. For even-distribution nozzles the planning literature specifies either no overlap (0%) or a deliberate 50% edge overlap. Anything between leaves a stripe.
• Working height fixes the spacing. The band width at the target distance sets the spacing, not the nozzle’s rated angle alone. A 65° nozzle at 300 mm throws a narrower band than the same nozzle at 600 mm, so the header spacing is calculated at the actual standoff.
• 5–15° offset also protects the header itself. Alternating the angle keeps the fan sheets from interfering with the mounting bar and from wetting adjacent nozzle bodies, which would cause drips.

These rules convert a row of flat fans from “a row of stripes” into “one even sheet”, which is the entire point of a header.

Need a Quote?

Send your band width, flow and fluid via the enquiry form and we will return a model and a header layout.

Related reading: flat fan header layout for spacing math, and how spray nozzles are made for orifice quality and wear.