Airless Spraying—From Pump to Pattern | Article 11 of 18
How to Prime and Start an Airless Sprayer
A Good Finish Starts Before Paint Reaches the Tip
An airless sprayer does not wake up ready to paint simply because someone plugged it in, dropped the suction tube into a bucket, and found the ON switch.
Before coating can be sprayed properly, the pump must establish material flow, air and incompatible fluids must be removed, the hose must be filled, and the complete system must be checked under controlled conditions.
Priming is not wasted time before the real work begins. Priming is the first part of the real work.
Inspect first. Prime at low pressure. Remove the air. Fill the hose. Test the pattern. Then begin production.
Priming and Purging Are Related—but Different
The terms priming and purging are sometimes used interchangeably, but they describe related parts of the startup process.
Priming
Priming establishes fluid flow through the pump. The fluid section must be filled so the pump can move material consistently rather than repeatedly drawing air.
Purging
Purging removes air, storage fluid, water, solvent, cleaning material, or a previous coating from the pump, return circuit, hose, and spray gun.
A pump may be primed while the hose still contains air or cleaning fluid. The complete system is not ready to spray until the fluid path has been properly purged and the intended coating reaches the gun consistently.
There Is No Universal Valve Position
Portable electric sprayers, gas-powered units, hydraulic airless systems, and pneumatic airless pumps do not all use identical controls or startup procedures.
One machine may use a PRIME/SPRAY valve. Another may use a bypass, return regulator, circulation valve, bleed valve, or different control arrangement.
This article explains the general sequence. The specific equipment manual determines:
- Valve positions
- Pressure-control settings
- Lubrication requirements
- Minimum hose length
- Grounding procedures
- Flushing materials
- Tip-installation timing
- Startup and shutdown steps
Use this article to understand what the process is doing. Use the equipment manual to determine exactly how your machine does it.
Step 1: Review the Equipment and Coating Information
Before operating the sprayer, review:
- The sprayer owner’s manual
- The spray-gun and tip instructions
- The coating product data sheet
- The coating safety data sheet
- The cleaning-material or solvent safety data
- Workplace ventilation, fire, electrical, and respiratory-protection requirements
Confirm that the sprayer, hose, gun, tip, filters, seals, and wetted components are compatible with the coating and cleaning material.
Do not assume that a flushing liquid suitable for one coating is appropriate for another. Waterborne, solventborne, plural-component, moisture-sensitive, and chemically reactive materials may require very different procedures.
Step 2: Prepare the Work Area
Startup can release coating, cleaning fluid, and vapors. The work area must be prepared before fluid begins moving.
Check:
- Ventilation
- Ignition-source control
- Equipment grounding
- Container bonding and grounding where required
- Approved waste containers
- Spill-control materials
- Personal protective equipment
- Safe routing of hoses and power cables
- Access to emergency equipment
Gas-powered equipment may have specific requirements concerning engine location, exhaust, fuel, and distance from flammable vapors. Pneumatic equipment requires a properly prepared compressed-air supply. Electric equipment requires the correct grounded power source and approved extension-cord arrangement.
Follow the exact manufacturer instructions and all applicable workplace and regulatory requirements.
Step 3: Inspect the Complete Sprayer
Do not begin startup with an inspection planned for later.
Before pressurizing the system, inspect:
- Suction tube, siphon hose, hopper, or material inlet
- Inlet strainer
- Return or bypass hose
- Fluid section and wet cup where applicable
- Prime, bypass, or circulation controls
- Filters and filter housings
- High-pressure hose and crimps
- Gun, trigger lock, and trigger guard
- Tip guard, seal, and tip
- Fittings, swivels, and connections
- Power cord, grounding conductor, air hose, or engine components as applicable
Look for cuts, abrasion, bulges, leaks, loose fittings, damaged threads, dried coating, missing guards, exposed reinforcement, and evidence of improper repairs.
Correct unsafe or questionable conditions before operating the pump.
Step 4: Service Lubrication Points as Required
Some piston-pump airless sprayers require approved piston lubricant or packing lubricant in a wet cup before operation. Other designs use different lubrication or sealed-fluid-section arrangements.
Use only the lubricant specified for the equipment, in the amount and location directed by the manufacturer.
Do not assume that every pump needs the same lubricant. The wrong material may be incompatible with packings, seals, or the coating.
Step 5: Prepare the Coating
The sprayer cannot correct coating that was improperly prepared.
Before placing the inlet into the material:
- Confirm the correct product and batch.
- Check expiration, induction time, and pot life where applicable.
- Mix the coating as directed.
- Condition it to the permitted application-temperature range.
- Strain it where required.
- Reduce or thin it only when authorized in writing.
- Confirm the recommended airless tip range.
- Verify that enough material is available to prime and spray.
Improper mixing, cold material, expired pot life, settled solids, skins, debris, or unauthorized thinning can create priming, filtration, atomization, cure, and performance problems.
Step 6: Identify What Is Already Inside the Pump
A new sprayer may contain factory test or storage fluid. A previously used sprayer may contain water, solvent, pump preservative, cleaning solution, or residue from another coating.
Before introducing the new coating, determine:
- What fluid is currently in the system
- Whether that fluid is compatible with the new coating
- Which intermediate flushing step may be required
- How the displaced fluid must be collected and disposed of
Water and a solventborne coating may not be directly compatible. Two different solvents may also be incompatible with each other, the hose, seals, or coating.
When compatibility is uncertain, consult the equipment, coating, and flushing-material manufacturers.
Step 7: Establish Pump Flow Through the Return Circuit
Many portable airless sprayers are initially primed through a return or bypass circuit.
The general process is:
- Secure the return hose in the proper waste or material container.
- Place the intake assembly into the approved flushing fluid or coating.
- Set the equipment controls to the manufacturer’s priming arrangement.
- Begin at the lowest recommended pressure or operating setting.
- Start the pump according to the model-specific instructions.
- Increase only enough to establish steady fluid flow.
- Allow displaced air and incompatible fluid to leave through the return circuit.
- Continue until the intended fluid appears consistently and without recurring air bubbles.
The return hose must be controlled. A loose hose can whip, discharge material unpredictably, or leave the container.
Do Not Run the Fluid Section Dry
Operating certain piston pumps without fluid can cause unnecessary packing and fluid-section wear. If the pump does not establish flow promptly, stop and diagnose the cause according to the manufacturer’s instructions.
Do not allow the pump to continue cycling while hoping it will eventually discover the coating.
Step 8: Move the Coating into the Pump
If the system was initially flushed with a compatible cleaning material, move the intake into the prepared coating according to the equipment instructions.
Continue through the approved return path until:
- The previous fluid has been displaced.
- The intended coating appears consistently.
- Air bubbles have been removed.
- The pump operates with a steady rhythm.
- The intake remains fully supplied.
Collect transition material separately when possible. Mixing contaminated transition fluid back into the coating may introduce water, solvent, dirt, or incompatible material.
Step 9: Purge the High-Pressure Hose and Gun
After the pump is primed, the hose and gun may still contain air or flushing fluid.
Follow the sprayer manufacturer’s procedure for directing material from the pump into the high-pressure hose and gun.
Depending on the equipment and material, the procedure commonly includes:
- Keeping the spray tip removed during hose purging
- Beginning at low pressure
- Directing the gun into an approved waste container
- Holding the metal portion of the gun against a grounded metal container where required
- Maintaining control of the gun and hose
- Triggering until air and previous fluid are displaced
- Continuing until coating flows steadily
The exact procedure depends on the equipment, coating, solvent, container, and hazard classification. Follow the model-specific manual.
The pump is not fully ready merely because coating appears at the return hose. The high-pressure hose and gun must also be properly purged.
Step 10: Check the System for Leaks
Once the hose contains material and the system begins building pressure, inspect the complete fluid path visually from a safe distance.
Check:
- Pump connections
- Filter housings
- Prime and return valves
- Hose fittings and crimps
- Swivels
- Spray gun
- Tip-guard connection
Never use your hand, glove, rag, cardboard, or paper to search for a high-pressure leak.
If leakage is suspected, stop the equipment and follow the complete pressure-relief procedure before inspecting or tightening anything.
Step 11: Install the Tip and Guard
If the tip was removed for priming and purging, engage the trigger lock and follow the complete pressure-relief procedure before installation.
Install:
- The correct tip-guard assembly
- The specified seal or gasket
- A correctly selected, serviceable spray tip
Follow the manufacturer’s orientation, tightening, compatibility, and installation instructions.
Never operate the gun without the required trigger guard and tip guard.
Step 12: Set Pressure and Test the Pattern
With the system properly assembled and ready for spraying:
- Begin at a low-pressure setting.
- Use a clean, appropriate test surface.
- Hold the gun at the recommended working distance.
- Make a controlled moving pass.
- Increase pressure gradually until the pattern is properly atomized.
- Stop increasing when the pattern becomes acceptable.
- Check for tails, pulsing, spitting, distortion, and excessive airborne coating.
- Verify wet-film thickness and finish quality.
A good startup ends with a verified spray pattern—not merely a pump that makes noise.
What If the Pump Will Not Prime?
If the pump does not establish steady material flow, possible causes include:
- Insufficient material in the container
- Intake assembly not fully immersed
- Clogged inlet strainer
- Loose suction connection
- Damaged suction hose or seal
- Air entering the intake side
- Stuck or contaminated inlet valve
- Prime or bypass valve not set correctly
- Material too viscous or too cold
- Dried coating inside the fluid section
- Worn packings, valve balls, seats, or other pump components
Do not immediately turn the pressure to maximum. High pressure does not correct an empty intake, loose connection, stuck valve, or blocked strainer.
Article 14 of this series will provide a complete pump-will-not-prime troubleshooting sequence.
Why Air in the System Creates Trouble
Trapped or incoming air can cause:
- Spitting at the gun
- Interrupted material flow
- Pulsing or surging
- Delayed pressure response
- An unstable spray pattern
- Inconsistent film build
Air may remain from incomplete priming or enter continuously through a loose suction fitting, damaged hose, low material level, or poorly positioned intake.
If bubbles continue appearing in the return material after the normal priming period, investigate the intake system rather than simply circulating longer.
Keep the Intake Supplied
A primed sprayer can lose prime if the intake draws air.
During operation:
- Monitor coating level.
- Keep the intake properly positioned.
- Prevent the inlet strainer from resting against and sealing to the container bottom.
- Watch for vortexing in shallow material.
- Keep dried coating and debris away from the intake.
- Prepare the next container before the current one runs empty.
Allowing the pump to empty the container can introduce air throughout the system and interrupt the spray pattern.
| Startup Observation | Possible Meaning | First Check |
|---|---|---|
| Pump cycles but no fluid returns | Intake restriction, air leak, valve issue, or incorrect control position | Material level, strainer, suction connections, and prime arrangement |
| Return fluid contains continuous bubbles | Air may be entering the intake system | Suction hose, fittings, seals, coating level, and intake position |
| Coating reaches the return hose but not the gun | Hose has not been purged or spray circuit is not established | Follow the manufacturer’s hose-purging procedure |
| Gun spits after coating appears | Air or previous fluid may remain in the hose or gun | Continue the approved low-pressure purging procedure |
| Pressure will not hold with the gun closed | Leakage, open return path, worn valves, or packing problem | Visual leak check, valve position, and manufacturer troubleshooting |
| Pattern has tails after priming | Pressure, tip selection, viscosity, restriction, wear, or capacity issue | Increase pressure gradually and evaluate the complete system |
Common Priming and Startup Mistakes
- Starting at maximum pressure: Priming and purging generally require only controlled, low pressure according to the equipment instructions.
- Ignoring the fluid already in the pump: Incompatible materials can contaminate the coating or damage equipment.
- Allowing the return hose to move freely: An unsecured hose can whip or leave the container.
- Installing the tip too early: Many systems are purged with the tip removed, but the exact procedure must come from the equipment manual.
- Running the pump dry: This can cause unnecessary fluid-section and packing wear.
- Returning contaminated transition material to the coating: Water, solvent, storage fluid, or debris may damage the batch.
- Checking leaks by hand: A tiny high-pressure stream can cause an injection injury.
- Beginning production without a pattern test: Coating reaching the gun does not prove that the system is ready to spray the work.
Airless Startup Checklist
- Read the equipment instructions and coating data.
- Prepare ventilation, grounding, waste collection, and personal protection.
- Inspect the intake, pump, hose, gun, tip guard, and fittings.
- Service required lubrication points.
- Prepare and strain the coating as directed.
- Identify and safely remove incompatible fluid from the system.
- Prime the pump at the approved low setting.
- Purge air and previous fluid from the return circuit.
- Purge the high-pressure hose and gun according to the manual.
- Check the system visually for leaks.
- Relieve pressure before installing the tip and guard.
- Begin with low spray pressure and test the pattern.
- Verify wet-film thickness before production.
Safety Notice: Startup Creates Pressure and Other Hazards
Airless spray equipment produces fluid pressure capable of penetrating skin and underlying tissue. Never point the spray gun at yourself or another person. Never place a hand, finger, glove, or rag in front of the tip or a suspected leak.
Keep the gun trigger locked except when the approved procedure requires controlled triggering. Maintain the trigger guard and tip guard in proper condition.
Follow the equipment manufacturer’s complete pressure-relief procedure before installing or removing a tip, tightening fittings, checking suspected leakage, cleaning filters, or servicing any component. Turning off the power source does not necessarily release pressure trapped in the hose and gun.
Flammable coatings and solvents may create fire, explosion, static-electric, inhalation, and contact hazards. Follow all manufacturer instructions concerning ventilation, grounding, bonding, ignition control, approved containers, flushing, personal protective equipment, and equipment location.
Use only hoses, guns, tips, guards, fittings, and accessories compatible with the materials and rated for the equipment’s maximum working pressure.
A suspected injection injury is a medical emergency. Seek immediate emergency treatment and provide medical personnel with information about the injected material. Do not treat the injury as an ordinary cut.
This article provides general educational information and is not a substitute for model-specific training. Always follow the current instructions and warnings supplied by the sprayer, gun, tip, coating, solvent, and safety-equipment manufacturers.
Check Your Understanding
- What is the difference between priming and purging?
- Why should the exact startup procedure come from the equipment manual?
- Why must you identify the fluid already inside the pump?
- Why is the spray tip commonly removed during hose purging on many systems?
- What can continuing bubbles in the return material indicate?
- Why is a pattern test required after the pump and hose have been primed?
If you can explain how to move from inspection to pump priming, hose purging, leak checking, tip installation, and pattern testing, you understand the purpose of a professional startup sequence.
The Bottom Line
A properly started airless sprayer has more than coating in the pump. It has the correct material throughout the fluid path, air and incompatible fluids removed, safe connections, a properly installed tip and guard, and a verified spray pattern.
Begin with inspection. Prime at low pressure. Control the return hose. Purge the pump, hose, and gun. Check for leaks without using your hands. Install the correct tip only after relieving pressure. Then test the pattern before coating the work.
A rushed startup may save a few minutes. It can spend the rest of the day returning them with interest.
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