When spray-coating atomization is poor, shop floors commonly make the following checks.

Is paint viscosity correct?
Is the thinner dilution ratio appropriate?
Is the spray gun functioning normally?
Is the nozzle free from clogging?
Is the operator’s spraying technique appropriate?

These are certainly important.

However, one cause is surprisingly easy to overlook.

It is the air-supply path to the spray gun, including hoses, couplers, fittings, and regulators.

The compressor gauge shows sufficient pressure.
The main piping appears satisfactory.
Yet the air is weak at the spray gun.

In such cases, hoses or fittings along the route may be bottlenecks.

Narrow hoses.
Excessively long hoses.
Couplers with small internal diameters.
Small fittings.
Filters approaching blockage.
Regulators with insufficient capacity.
Complex branched piping.

These may look like small components.
However, they substantially affect coating quality.

1. Having Pressure and Having Enough Air Are Different

Shop floors sometimes assume that conditions are satisfactory because pressure is available.

However, this requires caution.

Pressure is not the only important point in spray coating.
The required air volume must consistently reach the gun.

A water-supply analogy makes this easy to understand.

Even with high water pressure, a narrow hose cannot deliver sufficient water volume.
A blockage along the hose weakens flow at the outlet.
Conditions may seem sufficient near the faucet, but water volume can be inadequate at the end of a long hose.

Compressed air behaves similarly.

Even with pressure at the compressor, narrow hoses or fittings along the route may prevent the required air volume from reaching the gun.

Coating checks must extend beyond the compressor outlet.
Check air conditions at the spray-gun inlet during actual spraying.

2. Narrow Hoses Cause Insufficient Air Supply

An excessively narrow supply hose makes it difficult to deliver the required air volume to the spray gun.

Particular care is needed with guns that consume substantial air or when hoses run over long distances.

Narrow hoses cause the following problems.

• Pressure drops at the spray-gun inlet
• Atomization deteriorates
• Paint droplets become coarse
• The finish becomes rough
• Film thickness becomes uneven
• Operators try to compensate by increasing air pressure
• Paint losses increase
• Finishes vary between operators

A hose is more than a tube carrying air.
It is an important component supporting coating quality.

When old or temporary hoses are used for long periods, check internal diameter, length, deterioration, kinks, and crushing.

3. Excessively Long Hoses Increase Pressure Loss

Longer hoses create greater resistance to airflow.

This is called pressure loss.
Simply put, air loses pressure as it travels along the path.

Long hoses make pressure at the gun inlet more likely to drop.
Hoses running along the floor with numerous bends or kinks further restrict airflow.

Shop floors sometimes use long hoses for ease of work.
Workability is certainly important.
However, excessive hose length destabilizes coating conditions.

Check the following points.

• Is the hose longer than necessary?
• Is it kinked anywhere?
• Has it been stepped on and crushed?
• Has its inner surface deteriorated?
• Are multiple hoses joined together?
• Do hose conditions differ between operators?

Different hose conditions between operators can change the finish even with the same settings.

4. Do Not Overlook Coupler and Fitting Internal Diameters

Hose size may be checked while coupler and fitting internal diameters are overlooked.

A component that looks large outside may have a small internal passage.

A small passage in a coupler or fitting restricts airflow.
It is like a narrow bridge in the middle of a wide road.

Regardless of compressor capacity, a narrow section along the route constricts the air supply.

Check the following components.

• Couplers
• Sockets
• Nipples
• Elbows
• Regulator connections
• Filter connections
• Gun-inlet adapters
• Branch fittings

One small fitting can change spray-gun atomization.

To stabilize coating quality, identify the narrowest section of the entire air-supply system.

5. Regulators and Filters Also Create Resistance

Regulators and filters may be installed near the spray gun.

Regulators are needed to adjust pressure.
Filters are needed to remove moisture, oil, and dirt.

However, these devices also resist airflow.

Using an undersized regulator.
A clogged filter.
Equipment that is too small.
Long-overdue replacement.
Narrow connections.

These conditions prevent sufficient air volume from reaching the spray gun.

Filter clogging requires particular attention.
Filters remove contamination, but accumulated dirt makes it difficult for air to pass.

Installing a filter alone does not ensure adequate conditions.
Regular replacement and pressure-drop checks are necessary.

6. Highly Branched Piping Is Prone to Insufficient Air Supply

Coating shops sometimes branch one air line to several devices.

Manual spray guns.
Air-blow equipment.
Pneumatic tools.
Automatic machines.
Pumps.
Cleaning air.

When supplied from the same line, simultaneous use can cause insufficient air.

Even if normal conditions are satisfactory, pressure may drop at the following times.

• Several operators spray simultaneously
• Air blowing is used simultaneously
• Automatic machines operate
• Other processes consume large amounts of air
• Production volume increases
• New equipment is added

Insufficient air does not necessarily occur continuously.
It may occur only at certain times or under certain working conditions.

Check compressed air during peak use as well as normal operation.

7. Have Temporary Lines Become Permanent?

Temporary hoses or piping are sometimes installed for urgent shop-floor needs.

They may be necessary as short-term measures.
However, continued long-term use can cause quality problems.

Temporary piping is prone to the following problems.

• Excessively long hoses
• Narrow hoses
• Numerous fittings
• Numerous bends
• Floor-level routing exposed to foot traffic
• Air leaks
• No filters
• Condensate accumulation
• Different conditions between operators

Being usable for the moment differs from consistently delivering quality.

If temporary piping remains in use for a long time, consider replacing it with a properly designed permanent installation.

8. Check the Air-Supply Path When Changing Spray Guns

When introducing a new gun, examine more than the gun itself.

Required air volume varies by gun.
Higher-performance guns may need an appropriately matched air supply.

Hoses or fittings that worked with an old gun may supply insufficient air for a new one.

Low-pressure spray guns, electrostatic guns, automatic guns, and large-area guns, for example, have different requirements.

Check the following items when changing guns.

• Required air volume
• Recommended air pressure
• Nozzle orifice size
• Gun-inlet connection
• Hose internal diameter
• Coupler specifications
• Regulator capacity
• Filter capacity
• Number of guns used simultaneously

The air supply to the gun must be suitable for the gun to achieve its performance.

9. Insufficient Air Increases Operators’ Burden

Where air supply is unstable, operators try to compensate by intuition.

Change gun distance.
Change application speed.
Change output.
Increase air pressure.
Increase overlapping application.
Repeatedly touch up defects.

These responses burden operators.
They also increase variations between operators.

Skilled operators may compensate to some extent.
However, new or inexperienced operators find it harder to maintain quality.

Relying solely on operator skill to compensate for unstable equipment conditions does not show care for the shop floor.

Stabilizing the air supply creates an environment where operators can achieve quality without undue strain.

10. Air-Supply Problems Also Appear in Quality Data

Insufficient air caused by narrow hoses or small fittings may appear in quality data.

Examples include the following trends.

• Frequent rough finish with a particular operator
• Frequent uneven film thickness in a particular booth
• Poor atomization with a particular gun
• Defects increasing only at production peaks
• Coating quality worsening during air blowing
• Defect trends changing after gun replacement
• Frequent touch-up with no clear cause

In these cases, check the air-supply path as well as paint or operators.

Connect quality defects with equipment conditions in the investigation.

11. Common Hose and Fitting Issues in Factories in Vietnam

The following hose and fitting issues commonly arise in factories in Vietnam.

Using readily available components without further checks.
Not checking hose internal diameter.
Not checking coupler internal diameter.
Continuing to use old hoses.
Using temporary hoses as permanent installations.
Different hose lengths between operators.
Numerous joined hoses.
Insufficient flow through small regulators.
Late filter replacement.
Not measuring point-of-use pressure during airflow.

These conditions can leave insufficient air at the coating shop even with adequate compressor capacity.

Hoses and fittings are small components with a major effect on coating quality.

12. Basic Hose and Fitting Checklist

The following checks provide a practical approach to the shop-floor air-supply path.

1. Hose Internal Diameter

Check whether it is sufficient for the gun’s required air volume.

2. Hose Length

Check for unnecessary length or numerous joined extensions.

3. Coupler Internal Diameter

Check the internal passage diameter as well as external size.

4. Number of Fittings

Check for unnecessary fittings or excessive bends.

5. Regulator Capacity

Check whether capacity is sufficient for the operating flow.

6. Filter Condition

Check clogging, replacement intervals, and pressure drop.

7. Air Leaks

Check connections, hoses, and couplers for leakage.

8. Point-of-Use Pressure During Airflow

Check pressure with the gun actually triggered.

9. Simultaneous-Use Conditions

Check for insufficient air when multiple devices operate simultaneously.

10. Standardization

Check whether hose conditions vary between operators.

13. The Value CoatureVietnam Sees in Point-of-Use Air Diagnosis

CoatureVietnam does not assess coating quality solely through paint and operators.

We check whether air reaches the spray gun properly.

Compressor capacity.
Piping diameter.
Hose internal diameter.
Couplers.
Fittings.
Regulators.
Filters.
Point-of-use pressure during airflow.
Simultaneous-use conditions.

Checking these can reveal coating-defect causes.

Reviewing hoses or fittings may not require major equipment investment.
However, the benefits can be substantial.

Atomization stabilizes.
Operators make fewer adjustments.
Uneven film thickness decreases.
Rough finish decreases.
Paint losses decrease.
Quality becomes easier to standardize.

This puts CoatureVietnam’s guiding principle,
“Coating the Future with Science and Care”,
into practice.

Science means checking point-of-use pressure during airflow, air volume, hose internal diameter, and fitting resistance, and organizing causes numerically.
Care means creating a shop floor where operators do not have to compensate for unstable air conditions by intuition.

Conclusion

Narrow hoses or small fittings may seem like minor issues.
However, they substantially affect spray-coating quality.

Even with sufficient compressor pressure, a bottleneck on the route to the gun prevents the required air volume from reaching it.

Hose internal diameter.
Hose length.
Couplers.
Fittings.
Regulators.
Filters.
Branched piping.
Temporary hoses.
Simultaneous-use conditions.
Point-of-use pressure during airflow.

These checks are important.

Poor atomization, rough finish, uneven film thickness, paint losses, and excessive operator adjustment.
Air-supply problems may underlie these issues.

CoatureVietnam checks whether air reaches the point of use properly and provides improvement proposals that stabilize quality and reduce operators’ burden.