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Portable Plural-Component Coating Systems for Contractors

Article 08 of 24

Pails, Drums, Totes, Feed Pumps, and Material Supply

Ratio accuracy begins before the material reaches the proportioner. Containers, feed pumps, transfer hoses, agitation, temperature control, contamination prevention, and refill procedures must supply both components continuously and predictably.

The Supply System Is Part of the Proportioning System

A proportioner cannot meter material that does not reach its inlet consistently. Inadequate feed pressure, an empty container, a plugged suction tube, settled pigment, cold material, a collapsed hose, air entering a connection, or a moisture-contaminated hardener can interrupt component delivery and compromise the finished coating.

The material-supply system must be designed with the same care as the proportioner, heaters, mix manifold, hoses, and spray gun. It is not merely a collection of containers and pumps placed beside the equipment.

Learning Objectives

After completing this article, the contractor should be able to:

• Choose an appropriate supply arrangement for pails, drums, or totes.
• Determine when transfer pumps or pressure-assisted feed systems are required.
• Recognize conditions that can starve one side of a plural-component proportioner.
• Protect moisture-sensitive and contamination-sensitive components.
• Use agitation without introducing air or damaging the material.
• Plan container changes without losing prime, ratio control, or traceability.
• Apply safe handling, grounding, bonding, containment, and housekeeping practices.

Four Functions of the Material-Supply System

1. Store the components correctly. Each component must remain within the coating manufacturer's specified temperature, cleanliness, moisture-exposure, and shelf-life limits.
2. Maintain material uniformity. Components containing pigments, fillers, flakes, or other solids may require approved mixing or agitation before and during application.
3. Deliver each component continuously. The supply arrangement must meet the proportioner's peak inlet demand without cavitation, starvation, excessive pressure fluctuation, or air entry.
4. Protect the material from contamination. Dirt, water, incompatible solvent, cured material, condensation, or accidental contact between components can cause equipment damage and coating failure.

Choosing Between Pails, Drums, and Totes

Component A and Component B do not have to use identical container sizes. At a 4:1 ratio, for example, the contractor consumes Component A approximately four times as quickly as Component B by volume. Container and refill planning should reflect actual component consumption.

Never Identify Components by Color Alone

Every supply container, pump, hose, valve, filter, heater, and connection should be clearly identified as Component A, Component B, flush material, or another designated fluid. Color coding can support identification, but it must not be the only control.

Use durable labels that match the coating manufacturer's component designations. Prevent cross-connection mechanically where practical by using dedicated fittings, different connection sizes, keyed connections, or other positive controls. A mislabeled or cross-connected supply line can contaminate an entire component container and cure material inside the equipment.

Direct Suction Versus Transfer-Pump Feed

Selecting and Sizing Feed Pumps

A feed pump must provide sufficient volume at the pressure required by the proportioner without exceeding the allowable inlet-pressure limit. The largest available transfer pump is not automatically the best choice.

Evaluate the following:

• Required component flow at the proportioner's highest intended mixed output
• Component viscosity at the actual supply temperature
• Required inlet pressure and maximum allowable inlet pressure
• Container size, bung size, pump mounting, and immersion depth
• Pump ratio, displacement per cycle, air consumption, and operating speed
• Wetted-part, seal, packing, and hose compatibility
• Material sensitivity to air, moisture, heat, and shear
• Solids content, abrasiveness, fillers, and tendency to settle
• Pressure relief, isolation, filtration, and maintenance requirements

Component Demand Is Unequal at Unequal Ratios

Feed-pump sizing must account for the amount of each component consumed. At a 4:1 ratio by volume, every five gallons of mixed material theoretically contains four gallons of Component A and one gallon of Component B.

The calculation establishes theoretical component consumption. The selected feed pumps must also accommodate operating reserve, material properties, pressure losses, and the manufacturer's limitations.

Preventing Cavitation and Material Starvation

Cavitation or starvation occurs when a material pump cannot fill properly during its intake stroke. The pump may become noisy, cycle irregularly, lose pressure, deliver reduced volume, or introduce air into the system.

Common causes include:

• Material that is too cold or too viscous
• Undersized suction hose or feed pump
• Excessive suction-hose length or elevation
• Restricted inlet strainers, filters, valves, or fittings
• Loose fittings or damaged seals drawing air into the suction side
• A suction tube that is not fully submerged
• A blocked container vent or collapsed container liner
• Running the proportioner faster than the supply system can support

Material starvation is not corrected by increasing spray pressure. The restriction must be located and corrected before application continues.

Agitation and Material Uniformity

Materials containing pigments, fillers, reinforcing particles, or other solids may separate during storage. Follow the coating manufacturer's written mixing and agitation requirements for each component.

Effective agitation should:

• Maintain a uniform material composition throughout application.
• Reach material near the bottom and perimeter of the container.
• Operate at an approved speed without creating a deep vortex.
• Avoid whipping air or moisture into the material.
• Avoid excessive heat generation or mechanical damage to fillers.

Some components should be mixed initially and then maintained under slow agitation. Others should not be continuously agitated. The product manufacturer's instructions control.

Moisture-Sensitive Hardeners Require Special Protection

Isocyanate-containing and other moisture-sensitive components can react with humidity. The reaction may form skin, crystals, solids, gas, or other contamination that damages the coating and restricts equipment.

Depending on the material manufacturer's instructions, protection may include:

• Keeping the container closed except when an approved connection is installed
• Using sealed feed systems or approved desiccant breathers
• Using dry, properly conditioned air or an approved inert-gas blanket
• Avoiding wet tools, damp hoses, contaminated funnels, and open pouring
• Protecting partially used containers immediately after dispensing
• Following the manufacturer's limitations for opened-container storage

Do not assume that ordinary shop compressed air is sufficiently dry for direct contact with a moisture-sensitive coating component.

Material Temperature and Container Conditioning

Material temperature affects viscosity, pump loading, pressure loss, mixing, atomization, reaction rate, and cure. Conditioning only the fluid hose may not correct material that enters the proportioner at an unsuitable temperature.

A material-conditioning plan may include:

• Climate-controlled material storage before application
• Approved drum, tote, band, blanket, or cabinet heating
• Insulated supply hoses or enclosures
• Temperature measurement at the container and proportioner inlet
• Sufficient conditioning time for the entire material volume

Never apply uncontrolled heat to a coating container. The heating method, electrical classification, maximum temperature, sensor placement, and operating procedure must be approved for the material and location.

Container Changeover Without Losing Control

Container changes should be planned before application begins. The crew should know the minimum safe container level, who is authorized to perform the change, how the new container will be verified, and whether spraying must stop during the procedure.

1. Confirm the product name, component designation, batch number, shelf life, and container condition.
2. Verify that the new container has been stored and conditioned correctly.
3. Mix or agitate the component as required by the product instructions.
4. Stop or place the equipment in the approved changeover condition.
5. Prevent dirt, rain, condensation, and foreign material from entering open connections.
6. Transfer the pump or suction assembly using the manufacturer's handling procedure.
7. Re-establish prime and remove trapped air through the approved return or priming circuit.
8. Verify normal inlet pressure, pump operation, ratio status, and alarms before spraying resumes.
9. Record the new batch or lot number in the project documentation.

Never Run a Component Container Empty

Allowing either component container to run empty can introduce air, interrupt metering, produce off-ratio material, damage pumps, and require extensive repriming. A low-level alarm does not replace active container-level management.

Establish a minimum refill or changeover level based on container geometry, pickup-tube position, agitation requirements, component consumption, and the time required to complete a controlled change. Assign one crew member responsibility for monitoring each component supply.

Filtration Without Starving the Equipment

Inlet screens and filters can protect pumps and metering components from debris, but filtration must be approved for the material. A screen that is too fine can remove functional particles, load rapidly, or restrict a high-viscosity component.

Use the coating and equipment manufacturers' recommended filtration. Inspect filters at documented intervals, monitor differential pressure where provided, and investigate unusual debris rather than repeatedly cleaning the screen without finding the source.

Grounding, Bonding, Ventilation, and Spill Control

Where flammable or combustible liquids are handled, the contractor must evaluate ignition sources, ventilation, electrical classification, static electricity, container construction, and transfer procedures. OSHA requirements and other applicable regulations may require grounding, bonding, approved containers, and specific transfer methods.

• Ground equipment and conductive containers as required.
• Bond containers during transfers where required to maintain electrical continuity.
• Use conductive or static-dissipative hoses when specified.
• Keep clamps and contact points clean and attached to verified conductive surfaces.
• Provide secondary containment sized for the materials and containers present.
• Maintain clear access to exits, fire protection, shutoffs, and spill-control equipment.
• Follow the safety data sheet for ventilation, personal protection, storage, and spill response.

Nonconductive plastic containers require special evaluation. Do not assume that attaching a grounding clamp to plastic provides an effective static-control path.

Daily Material-Supply Inspection

Practical Field Rule

When a plural-component system develops unstable pressure, irregular pump movement, repeated ratio alarms, or inconsistent spray output, inspect the component supplies before adjusting the proportioner. Confirm container level, material temperature, agitation, inlet pressure, filter condition, hose restriction, pump operation, and the presence of air. Many apparent proportioner problems begin at the supply container.

Technical References and Further Reading

These official resources provide additional information concerning feed pumps, material containers, plural-component equipment, and safe liquid handling. Equipment examples are provided for education and do not constitute an endorsement.

• Graco, XM and XP Feed Pump Kits—Instructions: Official feed-pump instructions
• Graco, Feed and Solvent Flush Kits—Instructions and Parts: Official equipment manual
• Graco, XM Plural-Component Sprayers—Operation: Official operating manual
• WAGNER, TwinControl Operating Manual: Official operating manual
• Sames, Plural-Component Material Feeding Application Example: Official application information
• OSHA, 29 CFR 1910.106, Flammable Liquids: General-industry requirements
• OSHA, 29 CFR 1910.107, Spray Finishing Using Flammable and Combustible Materials: Spray-finishing requirements
• OSHA, 29 CFR 1926.152, Flammable Liquids: Construction requirements

Professional responsibility: Follow the current coating manufacturer's product data sheets, safety data sheets, mixing instructions, storage requirements, and application procedures. Follow the equipment manufacturer's limits for feed pressure, pump configuration, wetted-part compatibility, grounding, operation, and maintenance. Project specifications and applicable federal, state, and local requirements also apply. Obtain written clarification whenever requirements conflict.

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