Airless Spray

Airless spray derives its name from the fact that air is not used to atomise the paint (under high pressure), which is the opposite of conventional paint spray, where air is required to atomise the paint.

1. Airless spray equipment is by far the most commonly used for industrial and heavy-duty coatings applications, including solvent-free and fire protection systems.
2. This is an illustration of a protective coating being applied by airless spray to a steel structure.

Note: The compressed air or electricity supply powers the airless spray equipment.

Advantages of Airless Spray

There are several advantages to the use of airless spray equipment -

1. The equipment can apply a wide range of coatings.
2. Coatings can be applied very rapidly.
3. Thinning of coatings is not usually necessary. (check with the specific supplier).
4. High-build coatings can be applied easily.
5. Equipment is readily available with minimal parts.
6. Applicator training is available.
7. Minimal overspray compared to conventional air spray.
8. The equipment's capital cost is economical.
9. Mobile unit - only compressed air via electric or diesel compressors is required.
10. The equipment is robust, as it is often abused on construction sites and workstations.

Airless Spray Painting

Airless spray painting is particularly suitable for anti-corrosive and high-performance coatings applied to structures such as ships, bridges, rigs and tank coatings and linings.

1. This illustration shows an applicator applying an anti-fouling coating to the outside of a large vessel during dry docking.
2. The airless spray process is effective and efficient.
3. The process and application equipment are popular with industrial coating contractors.

Airless Spray Application

This video demonstrates the use of airless spray equipment to apply a primer coat to an abrasive blast-cleaned surface of a steel structure in a paint shop.

1. The airless spray equipment is ideal for this process.
2. By adjusting the tip and pressure, most coatings can be applied with ease.

Operator Training

Operator training is essential for using or assisting with airless spray equipment.

1. General equipment maintenance should be part of this operator training.
2. Spray painters should be familiar with all parts of airless spray equipment, specifically those related to Health and Safety.
3. Inadequate training will lead to potential health and safety issues and potential paint application problems.

Airless Spray Process 

The principle of airless spray equipment is that paint and coatings are pressurised, then travel through a supply hose to an airless spray gun and out of the orifice.

1. On clearing this orifice, the paint rapidly expands into a fine spray fan or atomisation.
2. This spray fan is controlled by the tip size, angle and pressure used during application.
3. The equipment size and ratio must be considered when deciding which size airless spray pump to use.

Airless Spray Tip

This illustration is a cross-sectional view of an airless spray tip.

1. The coating material is forced through the tip under constant pressure.
2. The pressure drop as the paint leaves the spray tip creates the spray fan used for coating application.
3. Various tip sizes and angles are available to suit the product and task.
4. Coating application sheets will usually define the tip size and angle.

Airless Spray Units

Airless spray units are designed with various ratios.

1. Examples of ratios include 30:1, 45:1 and 68:1.
2. The ratio of a pump is the relationship between the air pressure and paint pressure.
3. The applicator should consider the product, thickness, surface type, and pressure before determining the size of the spray unit.
4. Bigger is not always better when it comes to airless spray application.

This illustration shows the internal mechanism of an air motor in an airless spray unit.

What Does Ratio Mean?

If a pump has a ratio of 10:1, it means that the surface area of the air motor piston is 10 x greater than the paint piston surface area.

1. If you put 6.8 bar (100psi) air pressure onto the air motor, the resultant paint pressure will be 10 x greater, i.e. 6.8 bar (100 psi) air x 10 = 68 bar (1000 psi) paint pressure.
2. It is essential to understand the basics of ratios on an airless machine.

Airless Spray - Ratio

It's important to understand the airless spray equipment ratio.

This diagram illustrates two airless spray units with different ratios.

30:1 - When this is connected to an air line at 100 psi, the maximum fluid pressure will be 3,000 psi. (206 bar).

68:1 - When this is connected to an air line at 100 psi, the maximum fluid pressure will be 6,800 psi (468 bar).

The coating manufacturer will advise on the pressure requirements for their particular product. 

Piston Pump

This animation demonstrates the principle of a pump pressure ratio.

1. The piston on the left has twice the surface area as the piston on the right.
2. This principle is used with airless spray equipment.
3. Applicators should be shown the pistons during the training to gain an understanding of the principles.

Pump Lower Features

This illustration demonstrates the internal mechanism of a lower section of an airless pump.

1. The equipment should be high-quality, with parts manufactured from hardened stainless steel, tungsten carbide, chrome, etc. The packings can be seen along with upper and lower balls, pistons and a filter.
2. It is essential that reputable manufacturers supply the equipment and that only genuine parts are used.

Airless Spray Gun

This animation illustrates an airless spray gun in operation.

1. The paint is fed under very high pressure through to the spray tip.
2. As the trigger is pulled, the release of pressure creates a fan when the paint leaves the tip.
3. There are not many moving parts with an airless spray gun; however, most parts are under pressure, so the spray operator must be aware of the dangers when using the equipment or performing routine maintenance.

Viscosity

Viscosity and shear characteristics of a coating influence how it will atomise at a given pressure.

1. Viscosity is basically 'the resistance to flow'.
2. Thick oil will have a different viscosity from thin oil. The same principle can be used with paints.
3. Some paints' viscosities can change under the pressures and shear forces used.

Viscosity

This animation demonstrates two materials with different viscosities.

1. Viscosity can be adjusted by heat or solvent.
2. The higher type viscosity is usually higher solids and is used for high-build coatings.
3. A cold material can also have a high viscosity.

Viscosity

Solvent has a lower viscosity than water.

1. Coatings have a higher viscosity than water.
2. Viscosity can be affected by ambient temperatures.
3. Viscosity can be adjusted by adding solvents and thinners or heating the material.
4. Always check with the coating supplier for technical information on viscosity, heating, or adding solvents or thinners.

Thinning Paint

Thinning paint is often conducted on-site for the wrong reasons.

1. Thinning the coating material must be conducted in accordance with the coating supplier's recommendations.
2. Thinning does not affect the dry, as the additional solvent will evaporate as the coating dries. It does affect the wet-to-dry film thickness relationship (the volume solids changes).

Only add thinners if recommended by the coating supplier.

Paint Thinning 

This table illustrates how a chart can be used to calculate the new volume solids of a coating after adding a known quantity of thinners or solvent.

1. It is generally not recommended to thin a coating, as the coating should be delivered ready for use.
2. It is, however, common to find applicators adding thinners without reason, which can cause several problems for both the applicator and the product.

Note: the formula for calculating adjusted volume solids is; Volume solids / (100 + % thinner) = adjusted volume solids

The Main Components of Airless Equipment

1. PUMP - The airless spray pump pressurises the paint.
2. POWER - A power source (compressor or electric source) is required.
3. HOSE - High-pressure paint hoses.
4. CONTAINER - Holds the material.
5. GUN - Atomises and directs the paint onto the surface.

Only genuine parts must be used for the equipment.

Never purchase inferior or cheap replacements or spares.

Airless Pump

Airless spray units are supplied by reputable manufacturers throughout the globe.

All airless spray units are available with the manufacturer's instructions, which usually consist of the following:

1. Safety warning and details on the equipment and pressures.
2. Set-up procedure to be adopted before use.
3. Operational procedures for equipment use.
4. Description of parts.
5. Dimensions of equipment.
6. Troubleshooting and maintenance.

Most of the supplier's equipment manuals can be downloaded via the web.

The Pump

The most commonly used (and traditionally used) type of airless pump available to the paint sprayer is the pneumatic piston pump.  Electric airless are now becoming more commonplace. 

1. This unit is operated by compressed air and is widely found on sites and coating facilities.
2. The size of this airless spray unit varies depending on the specific process requirements.
3. Maintenance is usually only conducted when it stops working or breaks down!.

Airless Spray Equipment

This animation demonstrates the complete pneumatic airless spray unit in operation. (pumping the coating from the paint container to another).

1. Air is delivered to the unit by compressors via an air line to drive the air motor.
2. Suction hoses are attached to the airless unit and fed directly into the coating container.
3. Coatings should be flushed through as shown before use.

Airless Spray Pump

The only requirement for a pneumatic piston pump is compressed air.

1. Compressors are available in various sizes to suit the job's requirements.
2. Never exceed the safe working pressures on an airless spray unit.
3. Ensure all operators are trained in the basic operation of compressors and that the working manuals are available.

Note: compressed air is needed to operate the airless spray unit.

Air line

Compressed air from the compressor is routed to the airless spray via an air line.

The connection is usually a screw system, as illustrated.

1. Always ensure the air is clean and dry.
2. Do not turn on the air until the connection is secure.
3. Be aware of the pressures and turn the air on progressively.

Pressure

The maximum air inlet pressure should be embossed on the side of the airless spray unit.

1. Never ignore the safety advice.
2. Visual air gauges should be installed and working correctly.
3. Never ignore safety advice or warnings, as high pressure is used and can be very hazardous.
4. All the safety precautions will be detailed in the supplier's handbook.

Airless Spray Equipment

This illustration shows the components of an airless spray unit.

1. There are several parts on a typical airless spray unit that can be further divided into some very small parts.
2. All the information on parts should be in the supplier's instruction manuals.
3. Always have the manufacturer's instructions available.
4. The manufacturer's instruction manuals are generally available on the supplier's website.

Air Motor

Air motors for airless spray units are available in two basic types, depending on the age, size and type of manufacturer:

1. Differential motors.
2. Flat piston motors.

Airless Spray Air Motor

This animation illustrates the air motor on an airless spray unit with a differential type system.

1. The unit receives compressed air, which operates the piston arrangement.
2. The suction pulls the coating through the unit, ready for delivery.

Airless Spray Air Motor

This animation demonstrates the flat-piston air motor, which is very popular in spray equipment.

Compressed air is delivered to the head of the unit and then used to push down and lift the flat piston, creating suction and the unit's ultimate pressure.

Airless Spray Pump

This diagram demonstrates the airless spray unit in operation.

1. The paint or coating is placed under the airless spray unit, typically with a single leg.
2. The paint or coating is drawn into the airless spray machine via the fluid inlet, then forced under pressure into the paint line via the fluid outlet, and ultimately out of the spray gun and tip.
3. Air is used solely to operate the equipment.
4. The air is not mixed with the paint.

Suction Hose Filter

This video demonstrates a coating operative applying a filter to the suction hose on an airless spray unit.

1. The suction hose is the hose that sucks the paint from the container.
2. Purpose-made filters are also available, which attach to the suction hose.

Electric Airless Spray Equipment

Electric- and petrol-engine airless spray units are widely available.

1. Electric- and petrol-engine airless spray units are less popular than pneumatic pumps for heavy-duty industrial coatings. There is, however, an increase in electric airless units as the equipment gets faster and more efficient.
2. Electric airless spray units were very popular for commercial and decorative products; however, there has been an increase in their use for heavy-duty coatings.
3. Although obvious, an electricity supply is essential.

Electric Spray Equipment

As technology with airless spray equipment has increased, the use of electric spray equipment has also increased.

Once used for decorative and light-duty applications, the new types of electric airless can now apply more viscous, heavy-duty materials.

When using electric equipment, ensure the following:

1. The equipment instructions are read and understood.
2. The supplier or a qualified person gives an introduction to the equipment.
3. Power is available.
4. You are allowed to use electricity at the specific location.

Airless Spray Hose

A special airless spray hose is required to transfer the paint from the pump to the spray gun.

1. The hose should be designed and manufactured for use with high-pressure materials being pushed through.
2. Hoses should have a 4:1 safety factor built in when being selected.
3. Ensure the spray hose is supplied by a reputable supplier.

Paint Hose

When considering an airless spray hose:

1. Use reputable suppliers and manufacturers.
2. Use a high-quality hose, generally constructed with steel intertwined within the hose material.
3. The hose must have electric continuity.
4. Check that you have the correct pressure type.

Paint Hose Material

Paint hose material will consist of an inner tube, a metal carcass and an outer protective jacket.

1. The paint hose requires reinforcement due to the high pressure under which it is used.
2. Daily inspection is essential, checking for wear, tear and damage.
3. Ensure the paint line is not covered in paint, as this paint can hide defects in the paint line.

Airless Spray Hose

As the material passes through the paint hose, friction generates static electricity.

1. The static charge must be conducted back to the spray unit, where it is earthed.
2. It is essential to earth the airless spray unit during operation.
3. Paint hoses must also have electrical continuity.

Paint Hose Swivels

Hose swivels allow ease of mobility and flexibility at the spray gun, so the pressure is not working against the operator when spraying.

Without hose swivels, it can be challenging for the operator to manoeuvre the gun, especially in awkward locations.

As always, ensure you have genuine parts.

Summary

This training lesson introduced airless spray equipment.

We reviewed the principal use of airless spray, its advantages, and disadvantages.

We discussed how the 'ratio' works and gained an understanding of viscosity and its effect on coatings and spray equipment.

We also discussed electric airless machines and the main parts of a pneumatic airless machine.