All spray booths are designed to move air through a working chamber before exhausting it. They have three common components:
- Intake chamber
- Working chamber
- Exhaust chamber
Some spray booths also require air make-up units to operate efficiently and more effectively.
Located at the front or top of the booth, the intake plenum is the point at which air is brought into the spray booth. The plenum may be vertical and located at one end of the paint booth, or horizontal, using part or all of the ceiling inside the paint booth as an aperture. Air entering the spray booth through the plenum may flow parallel to the floor, or it may flow downward from an overhead plenum at the top of the chamber.
Dust, dirt and other airborne particles in the supply air are a major cause of contaminated paint jobs. A set of filters, located in the intake plenum, helps trap these particles before they enter the paint booth’s working chamber.
Since the paint booth’s working chamber encloses the spray operation, it should be large enough to contain the product and provide the painter room to move around the product. The recommended working depth in a paint booth is usually a minimum of 5 to 6 feet wider and deeper than the largest product to be coated. Lighting and vehicle movement are also considerations when designing a spray booth for painting and coating operations.
All dry filter spray booths use filters to capture overspray produced by the spray application. Filter materials are usually configured in one of two ways:
- Pads are suitable for operations in which overspray is concentrated in less than 50 percent of the filter area. Pads can be changed individually, as needed, reducing replacement costs.
- Filter rolls are a better choice when overspray is distributed across a majority of the filter surface. Filter rolls are purchased as bulk media and are traditionally cheaper than purchasing individual filter pads.
In some applications, water is used as the filtering medium. In water wash booths, a recirculation system continually cycles specially compounded water through a series of sluices and baffles, creating a water curtain to capture overspray.
In crossflow booths, the exhaust chamber is a plenum behind the exhaust filtration and is often the same width and height as the working depth. In this configuration, the exhaust air moves parallel to the floor as it enters the exhaust filters. In booths using downdraft airflow, the exhaust plenum is either a pit or a basement. Air from the working chamber is drawn down through filters under the booth to be exhausted or recirculated during a bake cycle. These exhaust systems typically use an air make-up unit to move air through the system.
Air Make-Up Units
During paint spray operations, the spray booth’s exhaust system removes a significant amount of air from the facility. A typical spray booth exhausts more than 10,000 cubic feet of air per minute (CFM). To combat this, shops may pull replacement air from outside the building. In colder environments, this replacement air can cool the interior of the building to an unsuitable temperature. An air replacement system, which supplies filtered, conditioned air to the booth, may be required. This minimizes temperature variations and removes particles that compromise finish quality.
Automatic Safety Shut-Down Systems: Automatically interrupts compressed air to the spray equipment (i.e. spray gun) when the accumulation of overspray in the filters exceeds a preset limit.
Dry Chemical Fire Suppression System: Pre-engineered packages specifically for spray booths. Fire suppression systems may require electrical service and compressed air.
Explosion-Proof Lighting: Recommended for hazardous locations, such as paint booths, shipyards, chemical manufacturers, oil drilling rigs and gas processing plants. UL listed for use in paint booths and paint mix rooms, UL 844 listed for hazardous locations and UL 595 listed for outdoor, marine-type lighting (salt water). Meets requirements for NFPA 33 and NEC Article 516.
Limit Switch: Electronically operated switch that shuts down painting operations when a paint booth’s doors are opened.
Manometer: Monitors air pressure within the working chamber. Also provides a visual indication of when dirty filters should be replaced.
Motors: All AC, polyphase induction motors should be mounted on standard NEMA frame bases and should be explosion-proof and totally enclosed, fan-cooled types. They should conform to state and local fire and safety regulations.
Pneumatic Start/Stop: Activates a pneumatic-electric interface, turning an exhaust fan on and off. A non-sparking pneumatic switch is located inside a paint booth, allowing the operator to enter and leave the booth with the exhaust fan turned off and preventing dirty, unfiltered air from entering the paint area.
Safety Air Valve: A three-port, two-position safety air valve prevents spraying with air assist systems when booth exhaust is off. Compressed air between the valve and spray equipment is vented out when the exhaust is shut off.
Variable Frequency Drive (VFD): Automatically adjusts fan motor speeds based on actual airflow conditions and maintains an air balance within the paint booth, preventing paint fumes from escaping and dust from entering. Also provides optimum air pressure, consistent exhaust and consistent temperature.