How much does the air cost that I use in my
Is air free? Technically, the air we use is free, but the cost
to compress that air is not. Factors to consider are:
- Local electrical costs
- Type of compressor
- Pressure used for spraying
- CFM consumed
- Amount of time the trigger is being pulled
- Number of coats being applied
- Efficiency of the gun/cap/tip combination
Before getting into the cost calculation, let's cover some of the
not so obvious factors.
The consumer type compressors that are bought from the big box
stores typically do not provide enough air volume/pressure for
individual applications. Two stage compressors provide the
higher pressures and volumes required.
The air pressure supplied to the spray gun should be set at the
lowest pressure that will allow the atomization required and still
allow the operator to accomplish the production required.
Higher than required pressures result in higher air consumption,
therefore higher electrical costs.
In general, it is more economical to apply the finish coat in one
pass than using two thinner coats. Less paint is used and less
electricity is used. Be sure to check your coatings Technical
Data Sheet for proper application and film builds.
To calculate the daily electrical costs for the air in a spray
gun use the following formula:
DC X HC X ED X CFM X .228
DC = DUTY CYCLE = PERCENT OF TIME TRIGGER IS BEING PULLED
HD = HOURS IN WORK DAY
EC = ELECTRICAL COST PER KILOWATT HOUR (.0935 NATIONAL COMMERICAL
AVERAGE, JULY '07
CFM = CFM RATING OR AIR CONSUMPTION OF THE GUN
.228 - ELECTRICAL CONSUMPTION OF 1 CFM IN KWh
For example, what is my annual cost to supply the air for my 18
CFM air cap. How much would I sve if I lowered my pressure to
a pressure that consumes 12 CFM or use a different air cap that
consumes 12 CFM?
My factors are:
- Duty cycles = 50%
- Work day = 15 hours
- Cost per KWh = $.10
- Days per year = 250
- 18 CFM Air Cap
.5 x 15 x .1 x 18 x .228 x 250 = $769.50 annual electrical costs
Compare the above to a gun/pressure combination consuming 12 CFM
.5 x 15 x .1 x 12 x .228 x 250 = $513.60 annual electrical costs
Lowering air consumption by using lower air pressures or using an
air cap with less air consumption would result in an annual savings
of $256.50 per spray gun.
The above calculation are based on typical efficiencies and are
approximate. The change in cost is
|| I cannot trigger my spray gun. What causes this problem? |
- Trigger safety is in the SAFETY position. Put trigger safety in SAFETY OFF position. Refer to your Instruction Manual for the operation of your particular spray gun's safety.
- The gun housing may be blocked from pumping a highly viscous material with a lot of filler that has packed behind the gun needle and will not allow the gun needle to move. Disassemble and thoroughly clean the spray gun.
|| What parts of the spray gun require lubrication? |
The fluid needle packing A, the air valve packing B and the trigger bearing screw C require daily lubrication with a non-silicone/non-petroleum gun lube. The fluid needle spring D should be coated lightly with petroleum jelly or a non-silicone grease (i.e.. lithium). Lubricate each of these points after every cleaning in a gun washer. |
|| What causes a top or bottom-heavy spray pattern? |
Horn holes plugged - clean holes with non-metallic point (i.e.. toothpick)
Obstruction on top or bottom of fluid tip - clean
Cap and/or tip seat dirty - clean
|| What causes the spray pattern of my airless gun to feather? |
|| The problem you refer to as feathering is also known as tailing. This is due to low fluid pressure at the tip. To avoid feathering or tailing, increase the fluid spray pressure by increasing the pressure at the pressure control knob. If the pressure control knob is turned all the way up you may have to thin the paint or reduce the length of airless hose being used. |
|| How should the air cap be cleaned? |
|| Remove the air cap from the gun and immerse it in clean solvent. If necessary, use a bristle brush to clean dried paint. Blow it dry with compressed air. If the small holes become clogged, soak the cap in clean solvent. If reaming the holes is necessary, use a toothpick, a broom straw or some other soft implement. Cleaning holes with a wire, a nail or a similar object could permanently damage the cap by enlarging the jets, resulting in a defective spray pattern. |
How can I make my tips last longer? What causes tip wear? |
tip wear on airless/air assist airless guns is caused by several
The pressure being used.
The size and shape of the tip.
The abrasiveness of the material being sprayed
The tip material
The higher the fluid pressure, the greater the wear.
Tip size and shape
Smaller tip sizes result in shorter tip life with other factors
Larger tip sizes result in longer tip life with other factors being
Shorter pattern sizes give longer tip life than taller pattern tips.
Highly abrasive materials will result in a shorter tip life when
compared to low or non-abrasive materials.
The quality of the materials will help determine tip life.
Higher quality materials like carbide, while more expensive to
manufacture, will not wear as quickly as carbon based material.
does tip wear affect my setup?
Flow rate increases
As the tip wears, the physical opening in the tip increases. An
increase from .015” to .017” (two one-thousands of an inch) may
result in a 33% increase in flow rates. How quickly this happens
depends on the factors listed above.
Pattern size decreases
The tip will wear out in the top and bottom portions of the tip
opening. This will result in a smaller pattern size. It will
continue to decrease in size as the tip wears.
does tip wear affect my spraying?
wear is gradual, usually over days or weeks. The operator will
attempt to compensate by doing the following:
Increase fluid pressure (an attempt to achieve an acceptable
pattern). This will increase fluid delivery even more.
Back away from the part (an attempt to achieve a larger pattern).
This may result in a dryer spray pattern.
Increase gun speed (an attempt to prevent runs and sags).
How long should a gun last before needing
to be rebuilt? What can I do to make it last longer? |
|| This depends on
what material you're spraying and how many gallons sprayed |
per day. For example, with lacquers, guns don't need rebuilding as
often because lacquers don't have solids in them. In contrast, the
high solids in blockfillers are abrasive and require more frequent
One way to increase gun life before repacking is to thoroughly clean
your gun at the end of every day. Be sure to trigger the gun before
removing the diffuser and when installing the diffuser. If you
don't, the diffuser will score around the ball on the new needle
which can lead to premature wear. Your gun will develop a leak and
this will cause spitting.
|| Why did my airless gun just stop spraying? |
|| The tip may be clogged. Turn the black plastic arrow shaped handle to the unclog position (arrow facing rear of the gun). Aim the gun into a waste paint container. Squeeze the trigger for a second. Return arrow shaped handle to the spray position (arrow facing forward) to begin spraying. Always set the spray gun trigger safety when working with the spray tip.
|| How long should a gun last before needing to be rebuilt? What can I do to make it last longer? |
This depends on what material you're spraying and how many gallons sprayed per day. For example, with lacquers, guns don't need rebuilding as often because lacquers don't have solids in them. In contrast, the high solids in block fillers are abrasive and require more frequent gun rebuilding.
One way to increase gun life before repacking is to thoroughly clean your gun at the end of every day. Be sure to trigger the gun before removing the diffuser and when installing the diffuser. If you don't, the diffuser will score around the ball on the new needle which can lead to premature wear. The gun will develop a leak and this will cause spitting.
|| My gun is spitting a small paint stream of paint after releasing the trigger and additional material is splattering on the surface. What's the cause and solution? |
|| The cause of the problem is that the needle is not seating properly in the seat. You will need to either purchase a kit for the gun needle and seat or you may only need to clean the needle and seat assembly. Residue or debris may cause the needle to move off to the side before seating. |
Tip extensions, extension poles and tip filters can also cause spitting or a stream of fluid after the gun is released due to decompression of the paint trapped between the gun and the tip. Fluid pressure dissipating through the tip causes this spitting or paint stream. An automatic shut-off valve will prevent this problem.
How do I know what size needle and nozzle is
best for the job? |
|| Although every job
may have slightly different requirements, for most materials it is
best to choose a mid-size, or No. 3, needle and nozzle. If
your paint is thicker than standard oil-based enamel, you may want
to consider a larger size. Remember that there is no one tip
that is perfect for all jobs. Needles and nozzles are quick
and easy to change out. So try different sizes until you find
what works best. |
Why am I getting a bad spray pattern, two
thick lines at the top and bottom of the spray pattern, or meager
flow from my tip? |
1. Tip is partially plugged. Reverse the spray tip and trigger the
gun to clear clog per instructions in your manual. Remove and clean
the tip, but do not use any metal objects to clean it with because
the tip carbide could be chipped and damaged.
2. Pressure switch is set too low. Increase pressure by turning the
3. Filters in sprayer or gun are plugged. Remove and clean the
filters or replace as needed.
4. Tip is too large or worn out. Replace the tip with proper size
for the material being sprayed and within the rated tip size of the
5. Material is too thick. Let the paint warm to room temperature if
the paint is cold or thin the paint according to the manufacturers
6. Paint hose is too long and/or too small diameter. Use shorter
and/or larger diameter hose.
7. Extension cord is too long or not a heavy enough gage. Use as
short of an extension cord as possible and it should be at least 12
gage or larger.
8. Valve seat, ball or gasket is worn out or valve may have been
loose, causing leakage and damage. Replace valve.
9. Pressure switch is defective/worn out. Replace pressure switch.
10. The suction hose is blocked, kinked, or cracked and leaking air
or suction filter is blocked. Examine the hose and filter and clean
or replace as necessary.
Why do I get streaks in my spray pattern?
Streaks in the spray pattern, especially heavy bands at the outside
edge, is an indication of low pressure at the tip. Turn up the
pressure control knob until these bands are eliminated. If the
sprayer is already at maximum, you may have to use larger diameter
hose or shorten the length of the hose to reduce the pressure drop.
Also, make sure any paint filters in the system are clean, because
there will be a pressure drop across a restricted or plugged screen.
Sprayers are rated for a maximum tip size. Using a tip that is
larger than the maximum size or a tip that is worn larger will cause
low pressure. The tip should also be the proper size for the type of
material being sprayed.
How do I choose an airless tip?
The size of an airless fluid tip will depend on
- The fluid delivery requirements.
- The size of the pattern required.
- The viscosity of the material being sprayed.
- The type and amount of solids in the material
- The type of filtration in the system.
- The pump pressure available
Let’s go through basic tip sizes first.
Fluid tips generally have a size listed in
thousandths of an inch. The size in normally the diameter of an
equivalent circle. Thus we may have 4 or 5 tips that have identical
opening sizes (ie .015”). While the sizes may be all the same, the
shape of the opening is not. Imagine taking a 15 in flexible circle
and changing the shape from a circle to an oval. How many different
size ovals could we make?
Tips may also have an indication of the pattern
size or angle of spray. That will vary with the manufacturer.
Looking at Figure 1, the areas of all the circles
are the same size.
Tip “A” would provide:
The least amount of resistance
The least amount of "tip plugging"
The least amount of tip wear
The shorter / rounder pattern
Tip “E” would provide:
The highest amount of resistance
The highest chance of "tip plugging"
The highest amount of tip wear
The taller / narrower pattern
Fluid Delivery Requirements
Most manufacturers have charts available that give
flow rates for various tip measured using oils of a specific
viscosity at specific pressures. A good rule of thumb for fluid
Doubling the fluid pressure will result in about a
40 percent increase in delivery.
Pattern Size Requirements
The choice of pattern size typically correlate
directly to the job at hand. Most manufacturers have several pattern
sizes available for a given tip opening. Match the size to your job
Higher viscosity materials will result in lower
flow rates. Another factor to consider is the temperature of the
coating material. Higher solids materials will be easier to spray
and atomize better if heated. Check your Technical Data Sheet for
the coatings maximum recommended temperature
Material solids directly affect the viscosity of
the material. Higher solids material typically require larger tip
openings. The particle size of the pigment will also determine how
frequently the tip ‘plugs’. Use larger tip sizes if tip plugging
Due to the narrow openings of most tips,
filtration is highly recommended. Passing the material through a
coarse strainer may be adequate on the shorter pattern tips, but a
fine filter usually is required for the taller pattern tips.
Use a pump that has enough pressure available to
do the job. You should try to size a pump for no more than 70% of
its rated pressure range
HVLP Spray Guns
Can latex be sprayed with an HVLP Spray Gun?
|| Definitely. While
most latex paints require some thinning for best results, the HVLP
is a great tool for applications. Consult your paint supplier
for recommended dilution amounts. Also, look for models with
pressure-fed paint supplies because they work best with latex and
other thick coatings.
My HVLP gets very hot after running for
awhile. Is this normal?
|| It is perfectly
normal. The turbines inside HVLP units run at a very high rpm,
which generates a large amount of heat. HVLP units are designed to
run effectively at high temperature levels. However, before
using the unit, always refer to the owner's manual for safety
HVLP differ from conventional air spray? |
utilizes the volume of air available at the air cap rather than
pressure to atomize. You will notice that all the orifices in an air
cap are larger in an HVLP air cap in order to allow the volume to
pass. HVLP air pressures are lowered internally in the spray gun air
passages. Conventional air spray gun will normally have the same
pressure at the air cap that was input to the spray gun. |
means High Volume Low Pressure, why am I using High Pressure (40 to
80 psig) at the gun inlet? |
compressed air, the lower the pressure, the smaller the volume of
air available. For example, air compressed to 40 psi contains 5
times the original amount of volume. Air compressed to 100 pounds
contains 8 times the original volume. Obviously at 10 psi to the
spray gun inlet, very little volume would be available for
available for all fluid feed systems (suction, gravity & pressure)? |
Yes. Keep in
mind that a suction feed gun depends on pressure at the fluid
tip/air cap junction to create a negative pressure in relation to
the cup atmospheric pressure. When using HVLP with 10 psi or less at
the air cap, very little suction is created. Use only low viscosity
materials with an HVLP suction feed gun |
HVLP technologies available? |
Industrial HVLP guns are commonly called conversion HVLP guns. They
use higher pressure air and convert it inside the spray gun. Another
form of HVLP is the turbine unit. Turbines are more typically used
in architectural or commercial applications. (Think of a shop vacuum
in reverse) |
required in all industries? |
Not at this
point in time. Even though some federal regulations restrict the use
of conventional air spray guns, it is typically only required for
"major emitters" as defined by the enforcing agency. Keep in mind
that any local jurisdiction may have their own requirements (ie.
Southern California) |
possible to exceed 10 psi at the air cap? |
air caps are typically rated for a maximum gun inlet pressure to
achieve 10 psi at the air cap. For example if 50 psi inlet achieves
10 psi measured at the air cap, then an inlet pressure of 60 psi
would exceed 10 psi at the air cap. |
How can I be
sure I do not exceed 10 psi at the air cap? |
2. Use an air cap test kit to measure the pressure at the air cap
Do I need to
use 10 psi at the air cap in order to atomize? |
necessarily. Use only enough air pressure (determines atomization
quality) and fluid pressure (determines production capability) to do
the job. Any pressure higher than that will increase over spray and
lower gun efficiency |
Are all HVLP
guns the same? |
like conventional guns, HVLP guns are available in different feed
methods, production and atomization capabilities. |
interchange air caps on HVLP guns? |
Yes and no.
It depends on the manufacturer and gun model |
some reasons HVLP might not work? |
air supplied. Restrictive quick disconnects and small inside
diameter air hose are the common culprits. Additionally undersized
compressors and low cfm regulators may cause problems. Another
problem is not matching the equipment to the application. For
example, trying to use a lower cfm air cap to spray high volumes of
technique different for HVLP?
Spray gun to
part distance typically is reduced to 6"-8" for HVLP compared to
8"-10" for conventional air spray guns
do you stop an airless spray gun from clogging?
most common techniques for preventing clogging of the spray gun are
to properly filter the paint, keep all dust and dirt from the
surrounding air from depositing into the paint reservoir, constantly
agitate the paint (without introducing air bubbles), and use the
correct tip size for the paint being used. When the gun clogs,
take a small sample of the paint that is clogging the gun and look
under low-power magnification to see if you can determine what is in
the paint that is causing this problem.
stainless steel mesh filter is placed at the end of the paint pickup
tube. For even better filtration (finer mesh), you might
consider wrapping some pantyhose around the stainless steel filter,
but first ensure that the pantyhose is not sensitive to any of the
paint ingredients, especially solvents. Some airless spray
guns provide a filter in the handle of the spray gun.
that you maintain the filter and keep it clean. Also look to
see there are not breaks in the mesh. You can also purchase
small filter washers that fit behind the fluid tip. The mesh
size on your airless spray gun might be to large, but you can often
purchase other sizes, such as 30, 60, and 100 mesh. If you use
a wooden stick or paddle to mix or stir the paint, do not allow any
old dry paint to enter the paint reservoir. Regular and proper
maintenance is the best preventative aid for clogging problems.
What criteria should be
known when selecting a Spray Gun?
selection of a spray gun is an important decision to make in the
design of a spray system. Matching the gun and fluid source to the
application is of utmost importance. Failure to choose the correct
equipment generally results in lower efficiencies, increased coating
costs, increased emissions, higher booth filter costs, etc.
match the spray gun to the application, the following criteria must
Generally listed as
high, medium and low - manufacturers' charts will usually indicate
the capabilities of their air caps and fluid nozzles in terms of
viscosity. If one knows the viscosity in centipoise or time in a
viscosity cup, it is a simple matter of conversion to the criteria
Generally listed in ounces, cc, ml or
gallons per minute - spray gun charts will generally indicate a
range of flow rates for a given fluid tip / air cap combination.
Production speed will dictate what the flow rate of the
equipment should be. Obviously, a line running a 30 feet per minute
with 6 square foot parts will require a higher flow rate than a line
moving at 10 feet per minute with 2 square foot parts.
Available Air (psi & cfm):
In most plants, the available air is adequate to supply the
necessary air required by a spray gun. Problems usually show up
Restrictive quick disconnects are used
Small I.D. air hoses are used (i.e.¼”)
Air hose longer that necessary is being used.
Compressors too small in size
Keep in mind, a typical industrial air cap consumes 20+ CFM
Fan Pattern Size:
Pattern size is one parameter listed for an air cap. It should be
matched to the part being sprayed. Pattern sizes range from as small
as one inch to several feet.
A “Class A” finish is not required for all applications.
Applying a finish to a garden utensil would not necessarily be the
same as the hood of an automobile. A stain applied to wood that is
to be wiped off would dictate a very low level of atomization. If a
lower level of atomization is required, an air cap with a lower CFM
($$$) would be selected.
Conventional Air Spray
Conventional air spray is the lowest in efficiency of
the different atomization types, but yields good atomization with
difficult to atomize coatings. Conventional air spray may not be
permitted by Federal, state or local rules for some industries.
HVLP (High Volume Low Pressure)
An air atomized spray gun with a limit of 10 psi at the
air cap. Since there is a legal limit (10 psi) in many cases,
choosing the proper air cap for the above criteria is critical.
Uses high fluid pressure (1000-5000 psi) to atomize.
Capable of very high flow rates, lower in atomization capabilities
than air atomized equipment.
Air Assist Airless
Uses high fluid pressure (300-1500 psi) to atomize. At
these lower pressures (compared to airless) the top and bottom of
the pattern have a difficult time atomizing. An air cap is added for
the sole purpose of eliminating the “tails”. Quality of finish is
between air atomized and airless guns.
Fluid delivery system:
Suction feed guns have been around for a century. While
they are simple to operate, they are the most inefficient of the
group. The range of motion is somewhat restricted since the pick-up
tube must remain in the fluid to function. It is available in
conventional air spray and HVLP
Gravity feed guns depend on gravity (cup is on top) to
supply fluid to the gun. As a result, some control of the gun is
gained over suction feed. Maximum use of the material due to gravity
is also a plus.
Allows maximum control of the required pressures (air and fluid).
The source of the coating is dependent on the amount used during a
given time period. Available sources include pressurized attached
cups, pressure pots (.5 to 60 gallons) and pumps (both low and high
the above criteria, a competent equipment supplier can match the
equipment to the application.
are the advantages of "triggering" a spray gun?
Triggering a spray gun refers to momentarily releasing the trigger
when the spray gun has passed the end of the part and is moving to
the position for the next spray pass. The amount of paint wasted
does not appear to be significant for those who do not release the
trigger between passes. The following example shows otherwise:
Operator spraying 50% of 7 hour day
Flow rate = 10 oz/min
Coating Cost = $10.00 / gallon
Trigger time = 1/5 (.2) second
the above figures:
lost at each spray stroke end
Part size requires 6 gun strokes
1 gun triggers per stroke, 6 Total
1 cc x 6 strokes = 6 cc lost per part
Production rate = 2 parts/minute
420 minutes x 2 parts / min. = 840 parts
840 Parts x 6 cc = 1.33 Gallons/Gun/Day
cc / gal
1.33 Gal./Day x 240 Days / Yr. = 319 Gal./Yr.
$10 Cost x 319 Gal. = $3,190 Finish Waste Per Year
$3,190 Lost For One Gun
Solids, 70% VOC
8 Lbs. / Gal x 319 Gal. = 2,552 Lbs. Liquid Sprayed / Yr.
2552 Lbs. X 70% = .9 Tons
2,000 Lbs ./ Ton
.9 Tons Emissions Generated by One Gun (applies against your VOC
Waste Disposal Considerations
Gal. X 30% Solids = 95.7 Gal. Solid Waste
95.7 = 1.74 Drums of Waste
Gal. / Drum
$200 / Drum Disposal Cost = $348
$348 Waste Cost Generated by one Gun
Total Cost of 1 cc Wasted per Gun
|@ $24 / Ton
Total Cost of 1
Obviously higher flow rates and higher coating costs would increase
the figures above. In addition to the above, increased booth filter
usage would be an issue.