A spray angle test plan defines the standardized experimental scheme used to quantify the divergence angle of sprays produced by trigger sprayers, aerosol actuators, hydraulic nozzles, and pharmaceutical delivery devices. This article presents a complete spray angle experiment plan covering sample preparation, instrumentation, measurement procedures, data evaluation, and applicable standards such as ASTM D7807 and the ISO 5682 series, giving engineers and quality professionals a reliable framework for spray characterization.
Technical Overview
The spray angle, also referred to as the spray cone angle or included spray angle, is the angle formed between two rays extending from the nozzle discharge orifice to the outer envelope of the spray plume. It is a primary geometric characteristic of any atomization device because it determines coverage width at a given spray distance, the spatial distribution of deposited liquid, and the overlap required between adjacent nozzles in multi-nozzle arrays. A spray angle experiment plan is the documented protocol that specifies how this parameter is measured, under which actuation or pressure conditions, with which instrumentation, and against which acceptance criteria, so that results are repeatable within a laboratory and comparable between laboratories.
Spray angle depends on device design factors such as orifice geometry, swirl chamber dimensions, and actuator insert configuration, as well as on operating conditions including pressure and flow rate, and on liquid properties such as viscosity, surface tension, and density. A rigorous test plan therefore fixes or records all of these variables. Accredited third-party laboratories typically structure such plans around recognized methodologies, including ASTM D7807 for the spray angle of trigger sprayers and the ISO 5682 series for agricultural spraying nozzles, supplemented by project-specific acceptance limits agreed with the manufacturer.
Testing Samples
The spray angle experiment plan should define the sample type, sample quantity, fill configuration, and sampling basis before testing begins. Typical sample categories are described below.
Trigger Sprayers and Finger Pumps
Trigger sprayers and finger pumps from household cleaners, horticultural products, and personal-care formulations are tested as complete filled units combining bottle and dispensing head. A common submission is 10 to 30 units drawn from three production lots to allow lot-to-lot comparison. Following the concept of ASTM D7807, both the initial spray angle, measured on the first actuation, and the steady-state angle, measured after priming actuations, are evaluated.
Aerosol Products and Actuators
Aerosol cans fitted with valves and actuators, such as air fresheners, insecticides, hairsprays, and spray paints, are tested at defined points in can life. Because propellant pressure and formulation concentration change as the can is discharged, the plan specifies measurements at the beginning of life, at approximately 50 percent dispensed, and at end of life. Actuator orientation relative to the target is fixed using a rigid fixture to eliminate operator influence.
Hydraulic and Air-Assisted Nozzles
Hollow-cone, full-cone, and flat-fan nozzles used in agricultural spraying, coating, cooling, humidification, and gas washing are tested on a nozzle bench at controlled liquid pressures, for example 1, 3, and 7 bar, using water of defined quality as the reference fluid. Flat-fan nozzles require the fan angle to be measured in the plane of the major axis of the footprint, while cone nozzles are measured on the projected plume outline. Air-assisted nozzles additionally require controlled atomizing air pressure and liquid-to-air ratio.
Pharmaceutical Spray Devices
Nasal spray pumps, metered-dose inhaler actuators, and oral spray devices are evaluated because spray geometry is a device-performance attribute that supports regulatory submissions. Testing is performed with the actual formulation or a placebo of matched viscosity and surface tension, at defined actuation force, stroke length, and hold time, after a documented priming sequence.
Testing Items
The core deliverable of the experiment is the measured spray angle, but a complete test plan typically includes the following items to make the result interpretable and defensible.
- Spray cone angle or fan angle at the nozzle exit, reported as the full included angle in degrees.
- Spray angle and footprint width at defined distances from the orifice, for example 100 mm and 300 mm.
- Spray pattern dimensions on an impingement target, including stain diameter for cone sprays and ellipse major and minor axes for fan sprays.
- Initial spray angle of the first actuation and steady-state angle after priming.
- Angle stability across unit life, for example beginning, midpoint, and end of a can or bottle.
- Angle versus pressure characterization to build an angle-pressure curve for hydraulic nozzles.
- Inter-unit variability expressed as mean, standard deviation, and relative standard deviation across the sample set.
- Simultaneously recorded flow rate or delivery weight per actuation to correlate geometry with output.
Testing Methods
Sample Conditioning and Preparation
Samples are conditioned at 23 ± 2 °C and 50 ± 5% relative humidity for a minimum of 12 to 24 hours before testing so that fluid viscosity, propellant pressure, and seal behavior are stabilized. Pump and trigger devices are primed with a documented number of actuations, which are discarded from data collection. Nozzles are inspected for manufacturing defects, and the orifice is cleaned with solvent and lint-free wipes to remove machining oils or particulates.
Direct Optical Imaging Method
The most widely used laboratory method captures a backlit side-view image of the spray plume using a digital camera or high-speed camera aligned perpendicular to the spray axis. A uniform backlight or a laser light sheet silhouettes the plume boundary, and image analysis software fits tangent lines to the outer spray envelope originating at the orifice. The included angle between the two tangent lines is computed automatically. The method is non-intrusive, captures transient behavior, and allows frame-by-frame averaging over the spray duration. Calibration is performed with a scale target placed in the spray plane.
Wetted Pattern Impingement Method
In this method the spray is discharged perpendicular onto a collector sheet such as water-sensitive paper, dye-impregnated paper, or a thin layer of development medium placed at a known distance from the orifice. The maximum wetted diameter is measured with a calibrated ruler or image analysis, and the spray angle is calculated trigonometrically as the included angle equal to two times the arctangent of the stain diameter divided by twice the spray distance. The method is simple, low cost, and well suited to field verification of agricultural nozzles, although it reports an effective angle at one distance rather than a continuous envelope.
Test Conditions and Instrumentation
A controlled test environment and calibrated equipment are prerequisites for valid data. The following conditions should be specified in the plan.
- Ambient temperature of 23 ± 2 °C and relative humidity of 50 ± 5%, recorded at the start and end of each session.
- Pressure supply regulated to within ±2% of the set point for nozzle benches, or fixed actuation parameters for pumps and aerosols.
- Fixed spray distance from orifice to target or camera focal plane, measured with a calibrated scale.
- Backlight intensity, camera exposure, and framing rate sufficient to freeze droplet motion without motion blur.
- Calibrated balance for shot weight, flow meter or graduated cylinder for flow rate, and calibrated pressure gauge transducer.
- Rigid fixtures to hold devices at a repeatable orientation and height, eliminating handheld variability.
Data Processing and Acceptance Criteria
For each device, a minimum of 10 valid actuations or steady-state image frames are analyzed. The reported spray angle is the arithmetic mean, accompanied by the standard deviation and the minimum and maximum values. Typical acceptance criteria are a mean angle within ±10 percent of the nominal design angle or within ±5 degrees, whichever is greater, with a relative standard deviation of no more than 10 percent across actuations. For pharmaceutical devices, tighter limits and additional statistical reporting are normally agreed with the sponsor. Any out-of-specification result triggers a documented investigation covering orifice inspection, pressure verification, and retest with fresh units.
Applications
Spray angle test plans are applied across consumer, industrial, agricultural, and regulated product categories. In consumer goods, manufacturers verify that trigger sprayers and aerosol actuators deliver consistent coverage and that design changes do not alter the user-perceived spray. In pharmaceutical development, spray angle and pattern data support device selection, comparability studies, and regulatory documentation for nasal and oral sprays. In agriculture, nozzle angle data drive boom height and nozzle spacing decisions so that overlapping flat fans produce uniform crop coverage, consistent with the intent of the ISO 5682 series. In fire protection, cooling, coating, and gas conditioning systems, the angle determines coverage and impingement behavior used in spray system design. Manufacturers also use the test plan for incoming component inspection, periodic production verification, and comparative benchmarking performed by accredited third-party laboratories.
FAQ
What is the difference between spray angle and spray pattern?
Spray angle is the divergence angle of the plume measured from the orifice, while spray pattern describes the two-dimensional footprint of liquid deposited on a target at a defined distance, including its shape, size, and uniformity. Both are usually measured together because they describe complementary aspects of spray geometry.
At what distance should the spray angle be measured?
There is no single universal distance; the plan must state and justify it. Optical methods often evaluate the angle within 50 to 150 mm of the orifice where the plume is fully developed, while impingement methods commonly use 100 to 300 mm to represent the real use distance of the device.
How many replicates are required for a valid result?
A minimum of 10 actuations per device and at least 3 to 10 devices per lot is typical, allowing calculation of mean, standard deviation, and relative standard deviation. Pharmaceutical and regulatory programs may require larger datasets defined in the study protocol.
Can the test be performed with water instead of the actual formulation?
Water is standard for hydraulic nozzle qualification because it enables comparison across designs, but formulation properties such as viscosity and surface tension measurably shift the angle. For product-release purposes, testing should be performed with the actual formulation or a rheologically matched placebo.
How does pressure affect the measured spray angle?
For most pressure-swirl and fan nozzles, the angle increases with pressure up to the design pressure and then tends to narrow slightly at very high pressures as the sheet contracts. This is why the test plan fixes the pressure or maps angle across a defined pressure range.
What standards govern spray angle testing?
Commonly referenced methodologies include ASTM D7807 for the spray angle of trigger sprayers and the ISO 5682 series for agricultural sprayer nozzles, together with product-sector and regional standards such as relevant GB and EN test method standards where applicable.