Advantages of Airless Spray

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

• The equipment can apply a wide range of coatings
• Coatings can be applied very rapidly
• Thinning of coatings is not usually necessary. (check with the specific supplier)
• High-build coatings can be applied easily
• Equipment is readily available with minimum parts
• Applicator training is available

Advantages of Airless Spray 

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

• Minimal overspray compared to conventional air spray
• The capital cost of equipment is economical
• Mobile unit - only compressed air via electric or diesel compressors is required
• The equipment is robust as it does get abused on some 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.

• This illustration shows an applicator applying a coating to the outside of a large vessel during dry docking
• The airless spray process is effective and efficient
• The process and application equipment is popular with industrial contractors

Airless Spray Application

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

• The airless spray equipment is ideal for this process
• 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.

• General maintenance of the equipment should form part of this operator training
• Spray painters should be familiar with all parts of airless spray equipment, specifically relating to Health and Safety aspects
• Inadequate training will lead to potential health and safety issues and potential paint application problems

Note: application of coatings to a vessel in a dry dock. Environmental policies vary globally about spray painting without any form of encapsulation

Airless Spray Process 

The principle of airless spray equipment is based on paint and coatings being pressurised so they travel through a supply hose to an airless spray gun and out of the orifice.

• On clearing this orifice, the paint rapidly expands into a fine spray fan or atomisation
• This spray fan is controlled by the tip size, angle and pressure used during application
• 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.

• The paint material is forced through the tip under constant pressure
• The pressure drop as the paint leaves the spray tip creates the spray fan used for coating application
• Various size tips and angles are available to suit the product and task
• Paint application sheets will usually define the tip size and angle

Airless Spray Units

Airless spray units are designed with various ratios.

• Examples of ratios include 30:1, 45:1 and 68:1
• The ratio of a pump is the relationship between air pressure into paint pressure
• The applicator should consider the product, thickness, type of surface and pressure before considering the size of the spray unit
• Bigger is not always better when considering airless spray application
• This is an illustration of an air motor demonstrating the internal mechanism

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.

• 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
• It is important to understand the basics of ratio on an airless machine

Piston Pump

This animation demonstrates the principle of a pump pressure ratio.

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

Pump Lower Features

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

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

Airless Spray Gun

This animation illustrates an airless spray gun in operation.

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

Viscosity

Viscosity and shear characteristics of a coating have an influence on how a coating will atomise at a particular pressure.

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

Viscosity

This animation demonstrates the two materials, each with different viscosity.

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

Viscosity

Solvent has a lower viscosity than water.

• Paint has a higher viscosity than water
• Viscosity can be affected by ambient temperatures
• Viscosity can be adjusted by adding solvents and thinners or heating the material
• Always check with the paint supplier for technical information on viscosity and heating or adding solvents or thinners

Thinning Paint

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

• Thinning of paint must be conducted under the recommendations of the coating supplier
• Thinning does not affect the dry as the additional solvent will leave the coating as it 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 paint after adding a known quantity of thinners or solvent.

• It is generally not recommended to thin paint as the paint should be delivered ready for use
• It is, however, common to find applicators adding thinners without any reason, which can cause several problems both for the applicator and the product itself

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

The Main Components of Airless Equipment

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

It is essential that only genuine parts are used for the equipment. Never purchase 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:

• Safety warning and details on the equipment and pressures 
• Set-up procedure to be adopted before use
• Operational procedures for the use of equipment
• Description of parts
• Dimensions of equipment
• Troubleshooting and maintenance

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

The Pump

The most common type of pump available to the paint sprayer is the pneumatic piston pump.

• This unit is operated by compressed air and is widely found on sites and coating facilities
• The size of this airless spray unit varies depending on the specific requirements of the process
• This picture illustrates how much abuse the airless spray equipment can get on sites when fully operational
• Maintenance is usually only conducted when it stops working or breaks down!

Airless Spray Equipment

This animation demonstrates the complete airless spray unit in operation.

• Air is delivered to the unit by compressors via an air line to drive the air motor
• Suction hoses are attached to the airless unit and fed directly into the paint container
• Paint should be flushed through as shown prior to use

Airless Spray Pump

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

• Compressors are available in various sizes to suit the requirement of the job
• Never exceed the safe working pressures on an airless spray unit
• 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

The compressed air is taken from the compressor to the airless spray via an air line.

The connection is usually a screw system, as illustrated.

• Always ensure the air is clean and dry
• Do not turn on the air until the connection is secure
• 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.

• Never ignore the safety advice
• Visual air gauges should be installed and working correctly
• Never ignore the safety advice or warnings as high pressures are used and can be very hazardous
• All the safety precautions will be detailed in the supplier's handbook

Airless Spray Equipment

This illustration demonstrates the various parts of an airless spray unit.

• There are several parts on a typical airless spray unit that can be further divided into some very small parts
• All the information on parts should be in the supplier's instruction manuals
• Always have the manufacturer's instructions available
• The manufacturer's instruction manuals will generally be found 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:

• Differential motors
• Flat piston motors

Airless Spray Air Motor

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

• The air is delivered to the unit via compressed air, which operates the piston arrangement
• The suction allows the paint to be pulled through the unit, ready for delivery

Airless Spray Air Motor

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

• Compressed air is delivered into the head of the unit and is then used to push down and lift the flat piston creating the suction and ultimate pressure in the unit

The Fluid Pump

The fluid pump is capable of delivering high pressures.

• It is essential that personnel operating the equipment are made aware of the high pressures involved
• The concept of 'divorced design' is often used to connect the air motor to the fluid pump

Airless Spray Pump

This video demonstrates the airless spray unit in operation.

• The paint or coating is placed under the airless spray unit and typically a single leg, as illustrated
• The paint or coating is drawn into the airless spray machine and then forced under pressure into the paint line and ultimately out of the spray gun and tip
• Air is used to operate the equipment only
• 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.

• The suction hose is the hose that sucks the paint from the container
• 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.

• Electric and petrol engine airless spray units are less popular than pneumatic pumps when using heavy-duty industrial coatings. There is, however, an increase in electric airless units as the equipment gets faster and more efficient
• Electric airless spray units are very popular with commercial and decorative products
• Although obvious, an electricity supply is essential

Electric Airless Spray Unit

This video demonstrates the setting up of an electric airless spray unit.

• Electric spray units are available in a number of sizes and are ideal for light-duty, commercial and decorative coatings
• Electric spray units have found an increased use for heavy-duty coatings due to better designs and higher pressures permitted

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 materials, the new types of electric airless can now apply more viscous and heavy-duty type equipment.

When using electric equipment, ensure the following:

• The equipment instructions are read and understood
• An introduction to the equipment is given by the supplier or qualified person
• Power is available
• You are allowed to use electric at the specific location

Power - (Airless Spray Pump)

There are three types of pump available:

• Pneumatic piston pump. Powered by compressed air
• Hydraulic Piston Pump. Powered by an electric motor or a petrol engine
• Diaphragm. Powered by electric motor, petrol and diesel engine

As always, get to know your type of equipment, particularly the safety details.

Power

Most heavy-duty industrial coatings are applied by the pneumatic airless spray unit.

• These spray units are (generally) available in various sizes, i.e. 65:1 or 68:1 ratio
• These airless spray units are commonly referred to as the 'contractors pump' as they are used by most industrial applicators
• An electric spray is generally used for light-duty coatings and decorative coatings
• The use of electric spray units is, however, on the increase due to current technology allowing more pressure, bigger size units and general availability

Airless Spray Hose

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

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

Airless Spray Hose

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

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

Paint Hose

When considering airless spray hose:

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

Paint Hose

The lining of the paint hose must be compatible with the material passing through it.

• The hose should have an adequate diameter to allow sufficient flow of material to pass through it without pressure drop
• The pressure drop is influenced by the material, viscosity, length and inside diameter of the hose
• Always check for leaks, signs of wear, tear and damage

Paint Hose Material

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

• Paint hose requires re-enforcement due to the high pressures under which it is used
• Daily inspection is essential, checking for wear, tear and damage
• Ensure the paint line is not covered in paint, as this paint can hide defects in the paint line

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 unit was an introduction to airless spray equipment.

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

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

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