AirSprayTech Academy Certificate Program
Portable Plural-Component Coating Systems for Contractors
Article 07 of 24
Selecting the Correct Proportioner for the Material and Project
A proportioner should be selected around the coating, required production rate,
application conditions, and support requirements—not around a brand name or an
impressive maximum-pressure rating.
The Central Selection Principle
The correct proportioner is the machine that can accurately meter the specified
components, maintain the required ratio throughout the usable operating range,
condition the material properly, overcome the restrictions of the complete fluid
path, and deliver the required production without exceeding the coating
manufacturer's limitations.
Equipment selection therefore begins with the coating manufacturer's current
technical data, application instructions, safety data sheets, and written
equipment recommendations. The proportioner is selected after those requirements
are understood.
Learning Objectives
After completing this article, the contractor should be able to:
- Identify the coating and project information required before selecting equipment.
- Distinguish advertised maximum ratings from usable operating capacity.
- Evaluate ratio, pressure, output, viscosity, temperature, and hose requirements.
- Choose an appropriate mix-manifold and mixer location for the material's working time.
- Compare fixed-ratio and variable-ratio proportioning systems.
- Consider serviceability, documentation, utilities, and total operating cost.
Begin With an Application Data Package
Before requesting an equipment recommendation, assemble a written application
data package. A supplier cannot make a reliable selection from the product name
and mix ratio alone.
|
Required Information
|
Why It Matters
|
| Product and component names |
Establishes the exact resin, hardener, catalyst, and thinner being used. |
| Mix ratio and allowable ratio tolerance |
Determines proportioning configuration and required accuracy. |
| Ratio basis: volume or weight |
A weight ratio cannot be entered as a volume ratio without converting for component density. |
| Viscosity of each component |
Affects feed requirements, pump loading, heating, pressure loss, and mixing. |
| Material temperature for the viscosity data |
Viscosity values are meaningful only when the measurement temperature is known. |
| Pot life or working time |
Influences manifold location, mixed-material volume, hose arrangement, and flushing procedures. |
| Required application pressure and spray-tip range |
Helps determine whether the system can atomize the material under actual job conditions. |
| Target wet-film thickness and production area |
Establishes the minimum practical mixed-material output. |
| Hose length, elevation, and expected temperature |
Affects pressure loss, heat loss, hose diameter, and system response. |
| Available electrical and pneumatic utilities |
Determines whether the complete equipment package can operate at the site. |
Ratio Range and Ratio Accuracy
Confirm that the proposed equipment can produce the coating's specified ratio
using the installed pump sizes, metering components, or control configuration.
A machine's overall advertised ratio range does not establish that every ratio
within that range is available in every mechanical configuration.
The coating manufacturer may specify a ratio tolerance. The contractor must
determine how the proposed system detects an off-ratio condition, how quickly it
responds, what causes an automatic shutdown, and what must be recorded during a
ratio verification.
If the product is specified by weight but the proportioner meters by volume,
convert the components using verified density values at the applicable
temperature. Never assume that a 2:1 weight ratio is also a 2:1 volume ratio.
Fixed-Ratio Systems
- Configured around one ratio or a limited number of mechanical ratios.
- Can be straightforward to operate and verify when matched correctly.
- Appropriate for contractors repeatedly applying the same material family.
- A new material may require pump, motor, or metering changes.
Variable-Ratio Systems
- Support multiple materials or ratios within the approved operating range.
- May provide electronic monitoring, reporting, alarms, and recipe control.
- Require correct programming, calibration, configuration control, and trained operators.
- Flexibility does not eliminate the need to verify each material setup.
Estimate the Required Production Output
Equipment output should be evaluated against the project's required application
rate—not simply against the largest number printed in a product brochure.
Theoretical gallons = Area in square feet × Wet-film thickness in mils ÷ 1,604
This is a theoretical volume calculation. It does not include surface
profile, overspray, material remaining in equipment, waste, or other losses.
Example
A project requires 4,000 square feet to be coated at 20 mils wet-film thickness:
4,000 × 20 ÷ 1,604 = approximately 49.9 gallons
If the crew must complete that application during four productive spray hours,
the theoretical average mixed-material demand is approximately 12.5 gallons per
hour. The contractor must then account for expected losses, interruptions,
surface geometry, required reserve capacity, and the need to operate the
proportioner within a stable—not marginal—part of its output range.
For a 2:1 volume ratio, approximately two-thirds of the mixed output is Component
A and one-third is Component B. The feed system, heaters, pumps, filters, and
containers must support the demand of each component independently.
Maximum Output Is Not Usable Output
Maximum-output ratings may be established under conditions that differ from the
proposed application. Actual delivery can be affected by viscosity, temperature,
inlet supply, pump speed, cycle rate, hose diameter, hose length, filters,
valves, mixer restriction, elevation, and spray-tip size.
The equipment should be capable of meeting production requirements without
continuously operating at its absolute limit. Reasonable operating reserve helps
accommodate cold starts, filter loading, changing hose conditions, normal wear,
and temporary production demands.
Pressure Must Be Evaluated Through the Entire System
The proportioner must generate sufficient pressure to move both components,
pass them through the metering and mixing system, overcome hose and accessory
restrictions, and provide the required pressure at the spray tip.
Maximum working pressure is a component limit—not a normal operating target.
Every fluid-carrying component must be rated for the maximum pressure the system
can generate. This includes pumps, heaters, filters, valves, manifolds, static
mixers, hoses, swivels, guns, fittings, and spray tips.
A high maximum-pressure rating does not compensate for inadequate flow,
undersized supply equipment, poor temperature control, excessive restriction,
or an incorrect metering configuration.
Viscosity, Temperature, and Material Conditioning
Obtain the viscosity of each component separately and confirm the temperature at
which each value was measured. Components in the same coating system can have
very different viscosities and may require different feed, heating, hose, or
pressure arrangements.
Material heating may reduce viscosity, improve flow, stabilize pressure, assist
mixing, and support atomization. Excessive heat can shorten working time,
accelerate reaction, damage material, increase solvent release, or exceed the
manufacturer's approved processing temperature.
Where heated hoses are required, evaluate their total length, wattage, insulation,
voltage, temperature-control method, sensor location, and ability to maintain the
approved temperature under actual ambient conditions.
Pot Life Determines Where Mixing Should Occur
Conventional plural-component coatings with sufficient working time may be mixed
at the proportioner and delivered through a mixed-material hose. Shorter-pot-life
materials may require the mix manifold to be located closer to the spray gun so
that the volume of catalyzed material is reduced.
Very fast-reacting materials may require impingement mixing at or within a
specialized spray gun. These materials should not be forced into equipment
designed for conventional static mixing unless the coating and equipment
manufacturers have approved the complete arrangement.
The selection must account for the volume between the mix point and spray tip,
expected pauses, reaction temperature, flush volume, flush time, and the
consequences of material curing inside the mixed-material path.
Material Compatibility and Wetted Parts
Review the compatibility of the coating components, approved reducers, and
flushing materials with every wetted component. Important considerations include
pump construction, seals, packings, hoses, O-rings, valve seats, filters,
manifolds, and mixer elements.
Filled, abrasive, moisture-sensitive, corrosive, or highly reactive materials
may require specialized pump designs, seals, stainless-steel passages,
corrosion-resistant parts, agitation, desiccant protection, or reduced filtration.
Written compatibility confirmation should be obtained when the equipment
documentation does not clearly address the material family being processed.
Site Utilities and Working Environment
- Compressed air: Verify pressure, volume, cleanliness, dryness, hose size, and compressor capacity.
- Electrical power: Confirm voltage, phase, frequency, amperage, connectors, extension limits, grounding, and generator suitability.
- Hazardous locations: Determine whether the equipment and accessories are approved for the classified location in which they will operate.
- Weather protection: Account for rain, dust, direct sunlight, freezing conditions, heat, and wind exposure.
- Mobility: Verify lifting points, trailer layout, weight distribution, access, hose routing, containment, and transportation requirements.
- Cleaning and waste: Provide an approved plan for flushing, collection, storage, labeling, and disposal.
Monitoring, Records, and Quality Control
Determine what the system monitors and what it merely displays. Depending on the
equipment, available functions may include ratio monitoring, pressure monitoring,
flow measurement, material temperature, pot-life alarms, batch totals, material
usage, fault history, data logging, and automatic shutdown.
Electronic monitoring can strengthen process control, but it does not replace
field verification. The contractor still needs written startup checks, ratio
verification, spray-pattern evaluation, wet-film measurements, environmental
records, maintenance records, and inspection documentation.
Selection Red Flags
- The required ratio is outside the approved equipment configuration.
- The supplier cannot explain how ratio accuracy will be verified.
- The required flow is below the machine's stable minimum or near its absolute maximum.
- Material viscosity is given without a corresponding temperature.
- The proposed hose length is not included in the pressure and temperature evaluation.
- The mixed-material volume is excessive for the coating's working time.
- Wetted-part compatibility has not been confirmed.
- Required utilities are unavailable or marginal at the project site.
- Replacement parts, qualified service, or operator training are not reasonably available.
- The recommendation is based only on pressure, price, or brand familiarity.
Evaluate the Complete Cost of Ownership
Purchase price is only one part of equipment cost. A responsible comparison
should include the complete spray package and the cost of keeping it productive.
- Feed pumps, agitators, heaters, heated hoses, manifolds, mixers, guns, and accessories
- Compressor, generator, electrical distribution, trailer, and containment requirements
- Startup materials, ratio-test equipment, spare parts, filters, seals, and repair kits
- Operator and technician training
- Flushing materials, mixed-material waste, solvent handling, and disposal
- Preventive maintenance and calibration
- Technical support, service response, parts availability, and downtime exposure
Practical Selection Procedure
- Obtain the current coating data sheets, application instructions, and safety data sheets.
- Document the ratio basis, allowable tolerance, component viscosities, temperatures, working time, and approved reducers.
- Calculate the project's required mixed-material output and component consumption.
- Define required pressure, spray-tip range, hose length, elevation, and mix-point location.
- Confirm wetted-part compatibility, heating requirements, feed equipment, and site utilities.
- Compare equipment within its stable operating range rather than by maximum ratings alone.
- Evaluate monitoring, shutdown protection, records, maintenance access, parts, service, and training.
- Obtain a written equipment recommendation for the exact coating and proposed configuration.
- Conduct a controlled material trial when the application is unfamiliar, critical, or outside documented experience.
Technical References and Further Reading
The following manufacturer resources illustrate the range of pressure,
proportioning, control, and application considerations found in portable
plural-component equipment. Product references are educational examples and do
not constitute an endorsement or replace project-specific engineering.
Professional responsibility:
Final equipment selection must be based on the coating manufacturer's current
written requirements, the equipment manufacturer's approved configuration, the
project specification, applicable safety requirements, and documented jobsite
conditions. Obtain written clarification whenever these requirements conflict.
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