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  • Airflow
  • Requirements
  • Velocity
  • Balance
  • Measuring
  • Exhaust Configurations
  • FPM Specs

1.3.3.a Airflow

Managing the airflow is probably the most important element of a spray booth and its design. Creating a laminar airflow envelope in the spray area at an engineered velocity separates a "spray booth" from a "tin box".

 

This managed airflow enables a painter to get maximum efficiency of the paint sprayed while directing overspray away from the painted finish. In a superior design, air is controlled to flow in unidirectional layers, either in horizontal, semi-downdraft or downdraft flow patterns, while maintaining an even velocity.

 

Velocity must be evenly maintained and BALANCED!

1.3.3.b Airflow

Booth Air Requirements

 

A critical step in selecting a spray booth system is establishing the minimum air velocity and volume requirements. The spray booth should be located to allow for proper air entry and flow through the booth.

 

The graphic at below shows that an open-faced booth should be located with the face at least booth height dimension from any wall. Booth "a" is too close to the building walls. The front of booth "b" is placed at a distance from the wall that is equal to the height of the booth. When this placement is not possible, air input plenums can provide adequate airflow. Booth "c" can be placed next to the wall because it has a direct-connected air input plenum.

 

A spray booth requires a minimum air draft or velocity, measured in lineal feet per minute (fpm), to carry overspray through the booth, past the operator or the automatic equipment, and deposit it into either the filter pads or water curtain. As a rule, OSHA inspectors rely on the guidelines specified in NFPA-33 requirements in the booth during spraying operations. While the NFPA-33 guideline covers most spray operations, greater airflow may be required when specific types of finishing equipment are used. The high-pressure atomization equipment used to break up higher solids materials, for example, produces high atomization pressures and consequently, high fluid stream velocity, at the tip of the spray gun. This can cause overspray to rebound and may expose the operator to toxic materials present in the paint. Velocity should always be sufficient to carry the overspray away from the operator and into the exhaust chamber.

 

The velocity possible in a booth depends on the fan size. Most standard booths offered in the market come equipped with fan and motor packages sized to deliver the necessary draft. Draft requirements take into account real world static pressures; that is, resistance to airflow from entry losses, stack filters and ductwork.

 

Static pressure is the amount of resistance air must overcome while moving from point A to point B. Static pressure in a spray booth is encountered in two areas:

 

-intake and exhaust filters, and;
-intake and exhaust ductwork.


The static pressure of any filter is determined by how much air will pass through that filter. Air intake filters for downdraft spray booths are denser and pass less air than air intake filters for either crossdraft or semi-downdraft booths. Consequently, air intake filters for downdraft spray booths have a higher static pressure rating than the air intake filters for other booths.

 

When intake or exhaust filters become clogged with dirt or material overspray, the amount of air that can pass through the filter decreases. When airflow is restricted, the filter's static pressure or resistance to airflow increases. Air intake and exhaust ducts also influence static pressure.

 

Air volume and velocity are decreased when elbows, reducers, transitions and long runs are added to ducts. Elbows introduce angles and increase resistance to airflow. Reducers and transitions also increase the static pressure in ductwork. The ideal situation is to keep ductwork to a minimum.

 

Static pressure is also a factor when choosing an air replacement unit. Because of the similarities to an exhaust booth, pressure drops in and out of the unit must be considered.

 

  • Overview
  • Creating Velocity
  • AIr Motivators
  • Pressurizing
  • Is Air Make-Up Needed
  • Air Make-Up Styles

1.3.3.c Airflow

Velocity

 

Some spray booth providers alledge that 14,000 and 16,000 CFM are what the user needs for today's new paints. Results from some recent testing debunk that allegation.

 

In May 2002, a well-known manufacturer spent some time at our Tech Center with a new paint product, trying to reduce the drying times even lower than he had previously achieved with our SmartCure™ process. Our Ultra cabin at the Tech Center can access either a 2-motor, 10 HP, 12,000 CFM generating group (air make-up system) or a 2-motor, 15 HP, 15,000 CFM Ultra generating group. Both units were used in the testing to see which one would cure the fastest.

 

The evidence was conclusive, and astonishing! The 12,000 CFM unit achieved a skin temperature of 140°F (60°C) faster than the 15,000 CFM unit, leading the paint company to conclude that there is / would be no advantage in using 15,000 CFM. In fact, the cost of operation would be greater, in view of higher-demand 15 HP motors and a larger burner.

 

 

Airlow Success Key #1

Velocity of the Air

Not CFM

 

 

All measurements should be made with a non-averaging velometer.
Measure at door handle height, completely around vehicle.

1.3.3.d Airflow

Creating Volocity


In order to achieve balance, a design must have a means of creating velocity. This is usually accomplished with a fan or blower on either the exhaust or supply or both.

 

The air velocity or ventilation rate must be sufficient to insure that the solid particles and flammable vapors are confined to the inside of the spray booth. The configuration of the object being sprayed plays an important role in determining velocity requirements.

 

For example:

 

-Manually finishing the interior of file cabinets would require higher air velocities to insure that the overspray is removed from the area between the finisher and the cabinet interior. This “capture” velocity can often be as high as 150 FPM with a conveyorized production system.


-Another example could be the finishing of large flat sheets. A high velocity spray booth would be necessary to ensure that the air movement around the edges of the large sheets would be adequate to prevent the overspray from rebounding and escaping from the inside of the booth.


-Tthe finishing of small objects with a lot of open spaces will allow the overspray to be captured with velocities of 125 FPM or sometimes less.


-Manual electrostatic spray guns, which are used to coat objects with open areas and objects that do not block the air flow, will allow overspray to be captured at velocities as low as 100 FPM.


In NFPA-33 (section 5-2) air velocity requirements are defined. According to the guidelines, a booth needs to "provide adequate ventilation to maintain the concentration of flammable vapors or combustible vapors or mists in the exhaust stream below 25% of the lower flammable limit (lfl) of the paint". Lower flammable limit is defined as the concentration level at which a particular atomized solvent will ignite.

 

The volume of air needed to move through the booth and into the exhaust chamber is measured in cubic feet per minute (cfm).

 

This is the formula for determining the volume of exhaust air:

 

Area x Velocity = cfm (cubic feet per minute of air)

 

Area is the cross-sectional area in square feet of all openings in the spray booth. When air input plenums are used the conveyor openings may be ignored. When connecting vestibules are used, the opening between adjacent booths may be ignored. Velocity is the speed or velocity of air required by code. Speed of air movement is measured in feet per minute (fpm). Cubic feet per minute (cfm) is the volume of air moving through the booth.

 

This relationship between booth size, the velocity of the air movement, and the volume of air being moved is shown in the graphic below.

 

To calculate the requirements for the booth in cubic feet per minute:

 

Multiply the cross-sectional area of the booth in square feet


by


the velocity of the air through the booth in feet per minute

 

10 ft x 12 ft = 120 ft2 x 100 fpm = 12,000 cfm

 

 

1.3.3.e Airflow

Air Motivators / Air Handlers / Fans

The terms "air motivator," "air handler" and "fan" are to some degree synonymous. All these devices cause air to move. How they make the air move, whether through blades slicing through the air, or via a "squirrel cage" which gathers and moves the air much like waterwheels powered the Industrial Revolution, is what distinguishes them apart.

 

There are currently three different types of air motivators, or fans, used in Global Finishing Solutions booths. The three types are:

 

1. Turbo fan (direct-drive, backward-inclined centrifugal blower), used in our Ultra groups and BT-1200 systems.
2. Tube axial fan. Tube axial fans appear in our BT-1200 and Expert systems.
3. Double-wheel, double-inlet squirrel cage blower, which is used in the Expert system.

 

Direct-Drive, Backward-Inclined Centrifugal Blower / Turbo Fan  

In an Ultra group or a BT-1200 system, the supply air is delivered by our direct-drive, backward-inclined centrifugal blower. In the Ultra group, this turbo fan also serves as the exhaust air motivator.

 

Direct-drive, backward-inclined fans:

 

-Maintain consistent air flow, even when the filters load up causing increased resistance. Less expensive fans just can't stand up to the pressure.


-Deliver higher performance with less horsepower, while consuming far less energy.


-Require much less maintenance because there are no belts, pulleys or bearings to replace.

 

The current unit is direct drive using a 10 HP open face motor. The blower wheel is directly attached to the motor shaft.

 

It is approximately 23" in diameter with 12 blades, each 6" long. The 7½ HP wheel is the same size, but the blades are only 4 inches long. The wheel is 12¾" wide from the inlet section to the discharge section. The wheel is steel with an aluminum inlet scroll, which meets the NFPA 33 code requirements about ferrous metal to ferrous metal in exhaust fans.

 

This design will deliver 12,000 CFM of air at 1750 RPM. The construction of the wheel makes it capable of delivering this airflow into a high static pressure situation.

 
Ture Axial Fan  

The main exhaust fan is mounted in a housing, which supports the fan blade in the middle of the duct and contains the motor mounting and belt housing. Fan sizes can range from 17-1/2" to 40". Some applications have required fans as large as 60", or 5 ft. Horsepower can range from 1/2 HP to 10 HP. The diameter of the pulley and the HP of the motor work together to create a specific CFM. On some systems, the speed is controlled by a VFD (variable-frequency drive).

 

Pulley alignment is very important in this fan. Ordinarily, a misalignment of more than 1/8" in one foot will adversely affect belt life. Improper pulley alignment produces vibration and uneven wear on one side of the belt. This causes the belt to roll over in the pulley, or throws the entire load on one side of the belt. The latter condition will result in stretching or breaking of cords on the loaded side. Once the pulleys are aligned, the belts also need to be properly tensioned.

 

The forced dry package uses a variable pitch pulley. The pulley setting should allow the booth to remain balanced. The fan motor is a 2 speed - 2 winding motor.

Double-Wheel, Double-Inlet Squirrel Cage Blower  

The supply air is handled by twin 15" DWDI (double-width, double-inlet) blower wheels mounted on a 4" tubular shaft. The blower wheels are attached to this shaft via two clamps (one on each side of the wheel). Two 3/8" socket head screws secure this clamp.

 

The shaft is hollow except for the end journals. This type of shaft is capable of spanning greater distances between bearings than a solid shaft style. Since this type of shaft can span more distance without whipping, the bearings can be mounted on the external face of the casing

 

Flange block bearings are used with eccentric locking collars. The bearings require greasing at least once every 6 months.

 

The drive assembly is made up of two pulleys. The driven pulley is a fixed or non-adjustable type. The driver pulley is a variable or adjustable type. The driver pulleys used on the 10,000 cfm and the 12,000 cfm cure units are identical. The one used on the 12,000 cfm unit is a 9.4 pitch diameter.

 

Pulley adjustment is only required if the blower speed needs to be changed to balance airflow with the exhaust system. All adjustments to the speed of the blower are done with the variable pulley.

 

The motor used on the supply blower is 10 HP. The RPM of the motor, depending on the manufacturer, is between 1750 to 1800. These motors are ODP (open drip-proof) style with standard T-frames.

 

The three-phase motors carry a voltage rating of 200-208/230/460. The 575 volt motor is a single rated motor.

 

The motor mounts right on the blower housing. Pulley alignment is very important in this fan. Ordinarily, a misalignment of 1/8" in one foot will definitely affect belt life. When the pulleys are aligned, the belts need to be properly tensioned.

1.3.3.f Airflow

Pressurizing a Booth

 

 

Because of the incredible volume of air needed to produce the velocity required for coatings operations, rather than drawing air from the area surrounding the booth, systems are fitted with air replacement or air make-up units so that they draw their air from the atmosphere through intake ducting. While passing through the air make up equipment, the air is not only filtered for atmospheric particulate (down to about 10 microns), but then may also be heated to a temperature specific to the application. This configuration assures even, continuous, filtered, tempered input air.


The term "pressurized" comes from the fact that inside the booth there is a slight "positive pressure". The dampers are set so that the tendency is for the air to push out of the booth. This prevents particulate in the area surrounding the booth to be sucked into the booth environment by negative pressure each time a door is opened.

 

1.3.3.g Airflow

Is Air Make-Up / Air Replacement Needed?

 

The terms "air make-up" and "air replacement" are interchangeable. In order to ensure proper air balance, air make-up or air replacement systems are designed to deliver fresh, filtered and heated air into a building or booth. In addition, an air make-up unit can lower heating and cooling costs. When air make-up is added, the building exhaust system works more efficiently.

 

What Air Make-Up Is

 

Air make-up is the air required to maintain safe and effective building operation by replacing exhausted air. When an exhaust fan is installed in a building, exhausted air must be replaced from outside. This is done either through the cracks and openings in a building or with an air make-up unit. The function of an air make-up, or air replacement, unit is to introduce outside air into the building. This air is usually filtered, cooled or heated.

 

Heating Air by Accident vs. Design

 

Installing an exhaust system without an air make-up unit is a good example of heating ventilation air by accident rather than by design. Air always flows from a higher-pressure area to a lower-pressure area. Installing an exhaust fan in a building creates negative pressure within the interior space. Air will flow from the higher pressure outside the building to the lower pressure inside.


Because most buildings are closed in, the flow is restricted, but not completely. Cracks around doors and windows and in the masonry and vent stacks allow air to flow into the building. This air creates drafts and cold spots until it can mix sufficiently with space air to reach room temperature. The normal heating system must work longer and at higher temperature to heat the air seeping from the outside. In addition to the increased heating cost, the negative pressure keeps the exhaust fan from doing its job — exhausting contaminants from the space.

 

When more air is exhausted from a building than is supplied by the mechanical systems, the building is under a "negative" condition and air will leak into the building through cracks, windows and doors. A negative condition results in the following:

 

-Flues and stacks will experience a backdraft and cause dangerous contaminants to remain in the occupied space. In the case of flues, the products of combustion may condense and corrode the equipment.


-The exhaust system sees a greater static pressure which reduces the capacity of each fan, resulting in an inadequate removal of contaminants and wasted horsepower.


-Drafts and cross currents will increase, causing an uncomfortable or unhealthy work environment.


Installing an air make-up unit sized to the building will improve exhaust system efficiency and provide greater control over the interior temperature. With the correct balance of air, it is easier to control air pressures to alleviate problems in opening or closing doors. Balance also prevents contaminants or odors from traveling to different areas of the building. The air make-up unit reduces fuel bills by eliminating drafts. Exhaust fans are rated for a certain air delivery measured in cubic feet per minute (cfm). This rating is based on a specific static pressure. Static pressure is the friction the exhaust fan must overcome to exhaust air. The more cracks and openings in the building, and the larger they are, the easier it is for air to move into the building. As the static pressure rises, the exhaust air decreases.

 

When to install an Air Make-Up Unit

 

The following checklist is helpful in determining if a building needs an air make-up unit:

-Gravity systems, such as vent stacks from a gas-fired furnace or water heater that normally draw air out of the building, are pulling outside air in.


-Exhaust systems are not operating efficiently, resulting in a build-up of contaminated air within the facility.


-The inside perimeter of the building is cold because the outside air is being pulled into the building.


-Exterior doors are hard to open or close because of the pressure exerted by outside air entering the building through them.


-It is difficult to maintain an even temperature throughout the interior space.

 

Sizing

 

The air make-up system should be sized according to the spray booth exhaust volume plus 10%. If the air make-up duct will be physically connected to the spray booth then the 10% extra capacity can be disregarded. However, some means of volume adjustment must be allowed so that a proper input/exhaust volume balance can be obtained. This can be in the form of an adjustable drive on the air make-up and/or exhaust fan or volume dampers in the system. If the installation is new, then the manufacturer will know the needs of both the exhaust fan and air make-up system. If the booth is older, the exhaust volume can be determined from the manufacturer's literature, computing from known booth velocity or from fan curves. Air make-up is most easily sized during initial booth purchase and installation.

 

To determine your air replacement needs:

 

-Multiply the exhaust fan rated capacity (CFM) by 20
(based on three changes per hour: 60 min. / 3 = 20)


Example:
10' wide x 8' high spray booth
Rated at 125 FPM
10,000 CFM
20 X 10,000 = 200,000 cubic feet of air


-If the shop area (width x length x height) is less than this amount, an air replacement system should be installed.

In the example above, the booth described would require an air replacement system in any building smaller than 100' x 100' x 20'.

 

 

1.3.3.h Airflow

Styles of Air Make-Up Units

There are four basic air make-up styles available. They are defined by their intake and discharge mechanisms and include:

 

 

Horizontal intake/downblast discharge

 

An air replacement unit for inside or outside installation. The unit, when weatherproofed, may go on the building roof, has a horizontal intake with a downblast discharge and is curb mounted.

 

Horizontal intake/horizontal discharge

 

An air replacement unit generally used indoors. The horizontal intake allows the unit to be mounted through the side wall of a building. The unit has a horizontal discharge.

 

 

Vertical intake/horizontal discharge

 

An air replacement unit for use indoors. The vertical intake allows for mounting through the roof of the building. It has a horizontal discharge.

 

 

Floor-mounted vertical unit

 

An upblast furnace. Horizontal intake and floor mounted vertical units are available in either inside or outside models.

 

 

 

  • Overview
  • Exhaust Airflow
  • Diffusing Airflow
  • Balance Control
  • Improper Aiflow

1.3.3.i Airflow

Airflow Success Key #2

Balanced air differential no greater than 20 ft./min.
(From one side to the other)

 

 

Balanced airflow and positive pressure — these are the hallmarks of a superior spray booth design, a design which incorporates an air make-up system to maintain positive pressure within the cabin, and uses an exhaust system, adjustable dampers and diffusion to control the balance.

1.3.3.j Airflow

Exhaust Airflow

 

The exhaust design should promote airflow completely balanced around the object, including the front, rear and sides. Unevenly balanced airflow creates conditions which encourage uncontrolled overspray migration onto the paint finish.

 

Critical, of course, is the exhaust filter itself. The various exhaust filtration media and their qualities and attributes are reviewed in detail in the Filtration Lesson. In every system configuration, all the parts of the filtration system must be maintained to O.E.M. (original equipment manufacturer) specifications. This is the only way to assure the proper airflow and a particulate-free environment.

 

The design of the exhaust "box" can vary from an engineered pit underneath the booth, or an exhaust chamber at one end of a booth, or exhaust outlets along the floor on each side of the booth. In downdraft booths, the preferred configuration is a continuous length "pit", spanning the enclosure end to end, which eliminates dead zones often associated with shorter pits. In other draft styles, exhaust chamber filter assemblies usually cover the entire wall in which they are installed. They can also be designed as "columns" - included within an exhaust yoke, usually configured around a large entrance door. No matter what the configuration of the exhaust, whether pit, chamber or yoke style, research and testing has revealed the necessity to maintain balance through the life of the exhaust filtration. This implies continuous monitoring of pressure, and adjustments and filter replacement when indicated by gauge readings.

 

1.3.3.k Airflow

Dissfusing The Airflow

 

Balancing the airflow in the booth is more than the total air in and total air out. There needs to be balance in the distribution within the booth. Complete system control requires engineered baffling and diffusion. This must be designed into the system to achieve the balance required around the painted object, and provide a consistent environment.

 

Air coming into the booth, whether through a plenum in the ceiling, or through an attached input plenum, or filter door, establishes the airflow in the booth. This entry point represents the first opportunity to influence and control airflow direction.

 

What is a "baffle"? Baffles are rigid constructions which are pierced or contain holes which permit air to pass through. Baffles can be made of paper, Styrofoam, metal or other materials. Their purpose is to force air to move in the desired patterns. This redirection of air is called "diffusion". Baffles diffuse airflow.

 

How can airflow be "engineered"? It takes testing, testing and more testing. In the situation illustrated below, an airflow meter, or velometer, is used to measure the speed of air. The floor of the booth is marked out in a precise grid using masking tape. The velometer's sensor is tightly taped to a camera tripod fitted with a plumb line, so that measurements will always be at a consistent height, and so that the instrument can be positioned precisely at the various grid intersections. As the tests reveal the results, various openings in the prototype baffles can be covered or uncovered to influence the next set of readings. When a satisfactory result is achieved, manufacturing can then retool or create a new part to conform.

 

 

This diffusion device has openings and bendable "wings" to redirect the airflow.

 

In some industrial situations, a booth can be engineered with an air input plenum, which is fitted with diffuser plates or baffles, which can be moved to alter the airflow

 

 

 

In addition, airflow in a downdraft booth is directly related to passage of air into the exhaust pit. Here is another opportunity to influence the movement of air, through diffuser pans below the pit filter. Here is an example of such a pan. Diffuser pans of engineered porosity lying below the pit filter regulate the flow of air into the exhaust chamber, and thereby, influence the pattern of airflow within the booth environment. Testing determines the optimal density of such pans.

 

 

 

 

Research has revealed that a downdraft input plenum design should cover as much as possible of the surface area available on the ceiling. The ideal design would be from wall to wall, providing a superior envelope of laminar airflow into the enclosure and around the object to be finished. Anything less than this surface area will result in poor airflow within the spray zone, leading to particulate migration and collection. This migration and collection will, over time, contribute to poor paint finishes requiring rework.


In horizontal flow and semi-downdraft flow booths, air arrives in the booth through an air input plenum or front filter door. The same objective is sought: the best balance possible in the finishing environment. Continuous pressure monitoring in these styles can minimize particulate migration and collection.

 

The objective is balance. The plenum design is critical in the effort to achieve the desired results.

 


1.3.3.l Airflow

Balance Control

 

How do all the parts work together to achieve the results we want? The proper airflow at the proper temperature is the goal we are trying to achieve. All the major components work to enhance, control or motivate the airflow. So understanding the airflow is most important.

 

Monitoring booth pressure is done through a differential pressure gauge. Pressure sensors are placed immediately in front of and after the filtration assemblies which are being monitored. The sensor should be kept clear of obstructions and paint buildup.

 

The balancing gauge monitors:

 

-Effectiveness of post-filtration assembly
-Booth pressure

-Effectiveness of exhaust or pit filtration assembly

 

Adjusting Booth Balance

 

Two types of differential pressure gauges are shown below. Either type can be used to indicate when the booth cabin is balanced and ready for spraying.

 

Gauges must be calibrated prior to use. To calibrate a gauge, first turn off the booth, open an access door and check location of needle.

 

Type A

 

With clean filters, the exhaust damper is adjusted to bring the gauge to .05 inches of water. The booth pressure should remain there during the paint cycle. If the supply blower and exhaust fan are adjusted properly with clean filters, the exhaust damper will be at approximately 45 degrees in the exhaust duct when this pressure is achieved in the booth on an Expert or BT system.

 

If the indicator on the gauge sets at .0, continue to spray cycle. To adjust, place a small screwdriver in the slot and turn right or left to reset indicator to .0. With the booth operating in spray mode, adjust the booth pressure by turning the knob until the indicator is between .0 and .05.

 

 

Type B (magnahelic gauge)


With clean filters, the exhaust damper is adjusted to bring the needle to the left side of the marked paint zone. The booth pressure should remain there during the paint cycle. If the supply blower and exhaust fan are adjusted properly with clean filters, the exhaust damper will be at approximately 45 degrees in the exhaust duct when this pressure is achieved in the booth on an Expert or BT system.

 

If the needle on this gauge is in the Paint Zone, continue to spray cycle. To adjust, place a small screwdriver in slot and turn right or left to reset until the needle is vertical. With the booth operating in spray mode, adjust the booth pressure until the needle is always in the blue spray zone.

 

As overspray continues to load the exhaust filter, the needle will move out of either spray zone. To bring the cabin pressure back to balance, manually adjust until the indicator reaches the spray zone. If the indicator still remains to the right of the spray zone, it is time to replace the exhaust filters.

 

Once the new exhaust filters are installed, check the position of the indicator and adjust if necessary.

 


1.3.3.m Airflow

Causes of Improper Airflow

 

Equipment out of adjustment or inoperative
- Supply blower
- Main exhaust fan
- Main exhaust damper
- Changeover damper (recirculating system)
- Burner profile plates and / or cold plates
- Discharge damper (forced dry system)


Foreign material blocks operations or airflow
- All ductwork
- Pit and / or tunnel
- All inlet or exhaust parts


Loaded, wrong, missing or incorrectly installed filters
- Plenum filters
- Pit paint arrestor
- Burner pre-filters


Incorrectly assembled ductwork or equipment


Too many elbow or transitions causing excessive pressure drop


Restrictive ductwork or transitions causing excessive velocity of airflow (particularly in the plenum)


Main exhaust stackhead incorrectly assembled; won't open completely


Changeover dampers

  • Measuring
  • Parameters
  • Taking the Measurements

1.3.3.n Airflow

Measuring Airflow

 

Knowing the airflow within the booth is critical. Measuring the airflow all around the vehicle or object being painted reveals whether the pattern of airflow is evenly balanced or not.

1.3.3.o Airflow

Parameters

 

2-motor Ultra generating package

 

Spray cycle set at 75°F (24°C)

 

Booth balanced

 

 

1.3.3.p Airflow

Single Center Pit

 

 

 

Measuring velocity at the grates

 

 

 

Measuring velocity at the vehicle

Twin Pit

 

 

 

\

 

Measuring velocity at the grates

 

 

Measuring velocity at the vehicle

1.3.3.q Airflow

Typical Exhaust Stack Configurations

 

Exhaust stacks are required to ventilate the booth to the outside.

 

-Stacks should be the same size and diameter as the fan.


-The stack should discharge vertically for adequate exhaust air flow.


-It is recommended that the stack extend a minimum of 6' above the roofline or as required by local codes.


The fan installed in the stack outside of the building, as shown at the right, is the preferred configuration.


Not only is the fan easy to reach for servicing, but the noise generated by the fan's RPM and the air velocity produced are kept outside of the working zone.

 

A stack section with "cleanout door" is installed directly below the fan to permit access to it for cleaning, servicing or replacement.

   

This configuration places the exhaust fan inside the building.


This can be a more costly solution because of the special muffler duct required to suppress sound the fan and air velocity will generate in the working zone.

 

The stack section with cleanout door is still in place next to the fan, and the special muffler stack section is directly below that.

 

1.3.3.r Airflow

FPM Specification for Various Applications

 

FLOOR TYPE BOOTHS
Based on Empty Booth
Velocity FPM Equipment / Application
50-100 Automotive refinish
100-125 Hand electrostatic - batch operation
100-125 Hand spray - batch operation
80-100 Automatic electrostatic - conveyor system
125-150 Hand spray conveyor system up to 10 FPM - small parts
125-150 Hand spray conveyor system up to 20 FPM - small parts
150 Hand spray - large parts
150-175 Automatic, air-atomized / airless

 

 

 

INDUSTRIAL DOWNDRAFT BOOTHS
Based on Empty Booth

Velocity FPM Equipment / Application
35-60 Automotive refinish
125 Side walls, pressurized - large objects only
125-150 Side walls, pressurized - large and small objects
150 Side walls, unpressurized
300-500 At grating, no side walls (velocity at breathing zone will be poor)

 

 

Global Finishing Solutions - The World Leaders in Paint Booth Technology- Paint Booths

12731 Norway Road • Osseo, WI • 54758 • info@globalfinishing.com • 800-848-8738