Falling film, rotary spray and rotary jet compared
The illustration shows two devices working in the same vessel: a static drilled spray ball on a fixed pipe and, beside it, an angled rotary nozzle throwing a narrower, stronger fan. They look like alternatives for the same job, but they clean by different mechanisms, and that decides how much water, time and chemical a cycle uses.
Covers how static spray balls, rotary spray heads and rotary jet heads clean tank walls: falling-film cleaning and wall shear stress, wetting rate and resource use, impact versus wetting radius, cleaning cycles and footprint patterns of rotary jet heads, and what to ask when replacing a static ball. Spray ball types, spray patterns, cleaning diameters by model and riboflavin coverage testing are on Spray ball; rotating head drive types, openings and cleaning-efficiency classes are on Rotating cleaning head; sizing supply flow, placing devices around obstructions and steam compatibility in CIP/SIP circuits are on Spray device for automated CIP/SIP.
CNFX editorial research · Sources checked October 12, 2026 · 3 sources
Fuchs and co-authors (TU Dresden and Fraunhofer IVV, Heat Exchanger Fouling and Cleaning 2013) state that with a spray ball or a rotating head the main mechanical cleaning effect comes from the gravity-driven falling film.
Alfa Laval, describing its rotary jet head in Manufacturing Chemist (2016), draws the contrast. A static ball delivers the larger part of its cleaning energy as water cascading down the wall at low wall shear stress, which has to be made up with time, water and energy. A rotary jet head throws concentrated jets: each jet hits the wall with an impact force, spreads into a footprint of high wall shear stress, and the head's 3D motion walks that footprint over the whole tank in a set pattern; shear falls with distance from the impact point.
A rotary jet head's pattern is built up in cycles. Alfa Laval says the first of eight cycles already covers the whole surface at an even but wide track spacing, which for an easy soil such as milk or syrup may be enough for the pre-rinse; one cycle takes 1 to 3 minutes, later cycles offset the tracks to close the gaps, and harder soils need more cycles.
Device
Main mechanism
What the sources say
Static spray ball
Falling film down the wall
Larger part of the energy as a low-shear cascade (Alfa Laval); falling film is the main mechanical effect (Fuchs et al.)
Rotary spray head
Rotating fans plus falling film
Falling film still the main mechanical effect (Fuchs et al.)
Rotary jet head
Jet impact footprint with high wall shear
Full pattern in eight cycles of 1–3 min each; first cycle covers the surface
A full eight-cycle pattern at 1–3 minutes per cycle is about 8 to 24 minutes (Editorial calculation). Alfa Laval says the higher purchase cost pays back in under a year in some installations; ask for the payback basis on your tank and soil.
02
Wetting rate: more is not better
Fuchs et al. measured film thickness by fluorescence on stainless steel plates tilted at 30° and cleaned a xanthan model soil with falling films.
They used volume flows of 93, 140, 192 and 236 l/h over a 0.1 m wetted width, wetting rates of 0.93 to 2.36 m³/h per metre. Wall shear stress and mean film velocity were the dominant factors for cleaning. Measured as cleaning per unit of liquid, the low flow (Re about 290) was about 60% more efficient than the high flow (Re about 734): a thinner film did more work per litre.
The condition is complete wetting. At the lowest flow the surface was not always fully wetted, so the tests pre-wetted the inlet area; in production the authors suggest a short initial high wetting rate to wet the wall, then a lower rate to clean.
Flow
Wetting rate
Finding
93 l/h
0.93 m³/h·m
Near the low-Re end; full wetting not always assured
236 l/h
2.36 m³/h·m
Thicker film; less cleaning per litre
Re ≈ 290 vs Re ≈ 734
—
≈60% higher fluid-mechanical cleaning efficiency at the lower flow
These are laboratory results on one model soil at 30° tilt; vertical tank walls and real soils differ. Ask the device supplier for the flow per metre of tank circumference at the operating pressure, and whether a high-flow wetting step is programmed before the cleaning flow.
03
Let the soil soak before the jets do the work
Yang, Wilson and co-workers (University of Cambridge, Chemical Engineering Science 208, 2019) cleaned thin toothpaste layers from vertical glass with horizontal impinging water jets and with the falling films the draining water formed.
They measured how soaking time changes the soil's rheology and the force needed to remove it, and how that changes cleaning. An adhesive removal model described the cleaning front produced by jets from both static and moving nozzles, and, once soaking kinetics were included, also described removal by the falling film. The authors present it as the first study of soaking effects on cleaning by water jets and falling films.
For tank cleaning this links the two halves of a cycle: a wetting or pre-rinse step does more than rinse, because soil that has soaked takes less force to remove, so the later jet impact or film flow has less to do. It is the same reason Alfa Laval's rotary jet head can clear an easy soil in its first pass and Fuchs et al. propose a short high-flow wetting step before a lower cleaning flow.
Cycle element
What the sources tie it to
Initial high-flow wetting
Ensures the whole wall is wetted (Fuchs et al.)
Soak time
Changes soil rheology and removal force (Yang et al.)
Jet impact or film flow
Removes soaked soil; jets clean a moving front, films clean by wall shear
The cycle sequence in the table is an editorial synthesis of the three sources. Ask the supplier how the recommended programme splits wetting, soak and cleaning flow for your soil, and whether it was validated on that soil.
04
What to give a supplier when replacing a spray ball
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
State tank diameter, height and volume, soil type and how long it sits before cleaning, supply pump flow and pressure at the device inlet, cleaning temperature and chemicals, and the current cycle time and water use. Ask which device type is proposed and on which mechanism it relies, flow per metre of circumference, whether a high-flow wetting step and a soak are programmed, the number of cycles for a full pattern on a rotary jet head, and coverage and cleaning validation on your soil.
Listed suppliers for spray balls and tank cleaning nozzles
3 companies list this product among what they make. Company figures are quoted from each
company's own website; every card states where the relationship came from.
China Sanitary Valve
TBC
China Sanitary Valve's site lists sanitary spray balls among its sanitary cleaning equipment, alongside valves, fittings and tank components.
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
How does a static spray ball clean?
Through the falling film running down the wall; Alfa Laval describes it as a low-shear cascade, and Fuchs et al. name the gravity-driven falling film as the main mechanical cleaning effect for spray balls and rotating heads. [2][1]
Does more cleaning flow clean better?
Not per litre: in Fuchs et al.'s tests the low flow (Re about 290) cleaned about 60% more efficiently than the high flow (Re about 734), provided the wall stayed fully wetted. [1]
Does soaking help?
Yang et al. found soaking time changes the soil's rheology and the force needed to remove it, and modelled cleaning by both jets and falling films once soaking was included. [3]
How long does a rotary jet head take?
Alfa Laval gives 1–3 minutes per cycle and eight cycles for the full pattern, with one cycle possibly enough to pre-rinse easy soils. [2]
Sources and what still needs a direct check
Sources checked 2026-10-12. Two peer-reviewed cleaning studies, one on falling films and one on jets, films and soaking, and a trade-press description of a rotary jet head.
