Spiral Spray Nozzles

A spiral nozzle has no internal vane, no swirl chamber and no removable insert. The liquid follows a helical ramp machined into a single piece of metal and leaves as a series of concentric cones. That one design decision, an open flow path with nothing narrow inside, is why spiral nozzles dominate duties where the liquid is dirty and downtime for unclogging is expensive.

They are not the most precise nozzle in the catalogue. What they are is the nozzle that keeps running when the water is recycled, gritty or carrying fibre.

Why the Open Path Matters

In a conventional cone nozzle, the pattern is created by forcing liquid through a swirl chamber or around a vane before it reaches a small orifice. Every one of those internal features is a place for solids to lodge. A spiral achieves the same rotational component externally, on an open ramp, so the narrowest point in the whole nozzle is the exit itself.

The practical consequence is a free passage substantially larger than a comparable cone nozzle at the same flow rate. Recycled scrubber liquor, cooling tower water and quench water all carry solids that a conventional cone would eventually catch.

Full Cone Versus Hollow Cone Spirals

Full cone spirals produce overlapping cones that fill the whole spray envelope, including the centre. Coverage is even across the footprint, which is what gas cooling, quenching and dust suppression want, the gas or dust has to meet droplets everywhere, not just at the edges.

Hollow cone spirals leave the centre open and concentrate the liquid into a ring. Scrubbing and absorption duties often prefer this, because the ring pattern presents more liquid surface area per litre to the gas stream, and the open centre lets gas pass without being shielded by a dense core of droplets.

The choice is not cosmetic: a full cone where a scrubber was designed for hollow cone changes gas-liquid contact and can measurably drop removal efficiency.

Droplet Size and Coverage Trade-off

Spirals produce a broad droplet distribution rather than a tight one. That is a consequence of the open design: without a precision swirl chamber, you get a range.

For gas cooling that breadth is often an advantage, fine droplets flash off quickly and the coarser fraction reaches further into the duct. For anything requiring a controlled droplet band, an air atomizing nozzle is the better tool.

Range Walkthrough: What Each Size Is For

The range table above lists all six sizes; this section says when each is the right answer. Flows and passages are quoted at 1.5 bar with clean water.

SP-1/8: the compact end of the range. Full cone, 1.5–7 L/min through a 2.0–3.5 mm free passage in a 1/8 in body. For low-flow injection points, pilot-scale scrubbers and small duct wash positions. Supplied in 316L or PP; few manufacturers even offer a 1/8 in spiral, so it is specified when the duty is genuinely low-flow.

SP-1/4: the smallest general-purpose size. Full cone, 4–11 L/min with a 3.0–4.5 mm passage in a 1/4 in body. Bench scrubbers, small quench points and washdown lances are typical homes. This is the first size with a PVDF option, so it also covers aggressive chemistry at low flow.

SP-3/8: where the free passage steps into extra-large territory: 5.0–8.0 mm at 12–46 L/min in a 3/8 in body. The passage clears the grit, scale and fibre in recycled water, which is why this size shows up on mid-size scrubber headers, cooling tower distribution and dust suppression at transfer points.

SP-1/2: the workhorse of the range. Full cone, 65–95 L/min through a 9.0–11.5 mm passage in a 1/2 in body. Main scrubber rings and flue gas cooling banks run on this size; the near-10 mm passage swallows the carryover solids that recirculated quench liquor accumulates.

SP-3/4: the step into high flow with a hollow pattern. 110–120 L/min through a 12–13 mm passage in a 3/4 in body. The dense rim and open centre suit gas-liquid contact columns and deluge-style fire protection, where the ring maximises surface area per litre.

SP-1: the top of the range. Hollow cone, 185–265 L/min through a 16–19.5 mm free passage in a 1 in body. FGD towers, large quench tanks and main deluge headers run at this flow, with nearly 20 mm of passage, nothing in recirculated liquor lodges in the body.

Application Matrix

Duty	Typical pattern	Suggested size	Why
Flue gas cooling	Full cone	SP-1/2 – SP-3/4	Coarse drops carry heat away fast; open passage tolerates carryover
Dust suppression / dust removal	Full cone	SP-3/8 – SP-1/2	Wide coverage and droplet momentum knock particulate down
Fire protection / deluge	Hollow cone	SP-3/4 – SP-1	High flow at low pressure, ring pattern with an open centre
Tank and equipment cleaning	Full cone	SP-1/4 – SP-1/2	Recycled or gritty wash water passes without clogging
Wet gas scrubbing	Full cone	SP-1/4 – SP-1/2	Even saturation of the gas stream; grit passes straight through
Quench tanks	Full cone	SP-1/2 – SP-3/4	Hot, dirty water at high flow: uptime is the spec
Cooling tower distribution	Full cone	SP-3/8 – SP-1/2	Even water over the packing; shrugs off scale and slime
FGD and chemical scrubbers	Full or hollow, PVDF/PP	SP-1/2 – SP-1	Acidic, abrasive liquor: chemistry drives the material

Three-Step Selection

When the checklist below feels heavy, the choice collapses to three questions in order:

1. What thread size? The header connection fixes the size class, and with it the free-passage class, from 2.0–3.5 mm at 1/8 in up to 16–19.5 mm at 1 in. If the water carries particles, this step is non-negotiable: a passage smaller than the largest particle blocks at the inlet whatever the flow.
2. What flow at pressure? Read the flow at your line pressure against the range table. Flow scales with the square root of pressure, so doubling pressure raises flow only about 40 percent. Spirals are low-pressure devices, size against the 1.5 bar reference, then confirm at line pressure.
3. Full cone or hollow cone? Even coverage of a surface or gas stream wants full cone; rim-only contact for scrubbing and deluge wants hollow cone. The vane cut sets the pattern, so specify it at order time, the body stays the same either way.

Where Eductors Fit

An eductor is a close relative worth knowing about. Instead of spraying into open air, an eductor nozzle uses the momentum of the pumped stream to draw in surrounding liquid, multiplying the volume moved without extra pumping capacity. Submerged in a tank, a small pumped flow can circulate several times its own volume.

That makes eductors the standard answer for in-tank mixing and keeping solids in suspension, where a spray nozzle would be the wrong device entirely. If your problem is stratified liquid or settling solids rather than surface cleaning, this is the direction to look.

Reference Specifications

Flow figures are quoted at 1.5 bar, which is the typical design point for spiral nozzles in scrubbing and cooling service. These nozzles run at low pressure by design.

How to Select a Spiral Nozzle

• Pattern requirement: full cone for coverage and cooling, hollow cone for gas contact and scrubbing.
• Solids content and particle size: this drives the free passage you need, and therefore the minimum nozzle size regardless of flow.
• Available pressure: spirals are low-pressure devices. Pushing them hard does not improve the pattern much and wastes pumping energy.
• Material: 316L for most scrubbing duties; PP, PVDF and PTFE where the liquor is aggressive; brass only for clean water service.
• Orientation: spirals can spray up, down or horizontally with the pattern intact, which is why they suit multi-level scrubber headers.
• Whether you actually need a spray: for in-tank mixing an eductor moves far more liquid per unit of pumping.

Frequently Asked Questions

Why is my spiral nozzle pattern uneven? Usually erosion of the spiral ramp after long service, or a partially blocked exit. Unlike insert nozzles there is nothing to replace internally, a worn spiral is replaced whole.

Can a spiral nozzle handle slurry? Mild slurries, yes, which is a large part of their appeal. Heavily abrasive slurries will erode the ramp over time, so hardened material or scheduled replacement should be part of the plan.

What pressure should I run? Most spiral duties sit between 0.7 and 3 bar. If your system runs much higher, check whether a different nozzle class fits the duty better rather than throttling to suit.

Are spiral and full cone nozzles the same thing? No. Full cone describes the pattern; spiral describes how the pattern is made. You can get a full cone pattern from a vaned nozzle or from a spiral, and they behave differently on dirty water.

Which spiral size do I need? Start from the flow at your line pressure and read the size off the range table, then check the free passage against your largest suspended particle. If the passage is too small, move up a thread size, the passage grows faster than the flow between steps.

Full cone or hollow cone for my duty? Even coverage, gas cooling, dust suppression, washdown, wants full cone. Gas-liquid contact, absorption and deluge systems want hollow cone, where the liquid sits on the rim and the centre stays open.

Why does my “anti-clog” spiral still block? Almost always the blockage is upstream, a strainer, a valve, or the line itself, not the nozzle. A spiral has no internal seat to sieve on; check the supply, not the body.

What should I send with an enquiry? Flow and pressure at the connection, pattern (full or hollow cone), fluid and temperature, largest suspended particle size, material requirement and quantity. That is enough to size the range for you.