Paint booths are highly controlled environments that aim to make spray painting safer, cleaner, and more efficient. Paints booths are made up of many components that operate in ways to improve safety and quality of the paint job. Let’s start out by introducing the actual components of a paint booth. This includes the following:
Paint Booth Walls
Main door openings in Paint Booths can be covered in many ways These are the following: Single Skin, Dual Skin Insulated, Barn Doors, Tri-fold Doors, Bi-fold Doors, Sliding Doors, Roll-up Doors, Sliding or Roll-up Curtains. Doors are used in enclosed booths. There are Open Face Booths that do not have doors as well.
The Intake Plenum is another important component of the paint booth. It is a chamber that is connected to the paint booth to bring air into the booth. It generally does so through intake filters. These function to spread the air out for a laminar flow into the paint booth cabin. This plenum can be located on the end of the paint booth or on the ceiling. There are different types of filters that can be used to clean the air before it enters the booth. General 20” x 20” filters are used all the way up to large downdraft diffusion media.This type of filter is more restrictive and requires a stronger fan to push air through it. It does filter the air to a smaller size of dirt.
Exhaust Chamber, Pit, And Plenum
The Exhaust Plenum is a chamber that is connected to the paint booth to remove particulates before the air is exhausted outside. The plenum can be located at the end of the paint booth, low in the side walls or in a pit in the floor. There are different types of filters that can be used to clean the air before it is pushed back outside. General 20” x 20” filters are used all the way up to large exhaust blankets.
Air Make-Up Unit
An Air Make-Up is a type of blower that functions to make up for the air that is lost as a paint booth pulls air into it for its operation. If the paint booth pulls 10,000 cubic feet per minute (CFM) out of a building an air make-up needs to be installed to push 10,000 CFM back into the building. It is a violation of Commercial Building Code to operate a building under negative pressure. An air make-up can be connected right to the paint booths intake plenum. That forms a closed loop system. This type of system keeps everything cleaner and doesn’t involve the building systems at all. Most air make-up units used on paint booths also employ heat. This is helpful in the winter months. Paint must always be painted in the 68 to 78 degree fahrenheit range.
Manometers (Dirty Filters)
A Manometer is a device that lets the operator know the level of restriction in the booth exhaust filters. The more paint that is sprayed in the booth, the more restricted the exhaust filters become. It is a general rule that when the exhaust filters get between 0.25” – 0.50” of water column above the clean level of the exhaust filters that they need to be replaced
How Paint Booths Actually Work:
The paint booth consists of one or more powerful fans to move air through the paint booth. An operator (painter) sprays paint onto an item. While doing this some of the paint either bounces off of the substrate (surface of item being painted) or does not land on the item well enough to flow in with the rest of the paint. This is generally referred to as overspray.
Part of the composition of the paint booth are intake filters to filter the air of dirt that is coming into the paint booth and exhaust filters. These filters are meant to capture the overspray particles before the air is pushed back outside. Because paint can be flammable, the paint booth has provisions designed into it to mitigate the dangers to personnel and property when spraying these explosive chemicals.
The most common components of paint booth design can be thought of as the air is taken through the cycle of using a paint booth. Air comes from outside the building generally through a steel piece of duct work into a blower unit. This blower unit pushes the air through the intake filters into the paint booth cabin. The blower unit can have a heater installed in it for use on cold days. It can also be used after painting to increase the temperature of the air in the booth to bake the paint on. After the air leaves the intake filters it is directed to the article being painted. The speed of that air is moving at 1 to 2 mph or 80 to 150 ft per minute. This is fast enough to gently sweep the overspray away but not so fast as to have the paint dry too fast.
The air is now being pulled by another fan into the exhaust filters. Here the overspray is removed and the air is then sent back outside through a similar steel duct. Because the paint booth is meant to contain the hazards associated with spraying flammable and potentially explosive chemicals, its construction is regulated by a number of commercial building codes. These codes state that the unit must be built out of steel of a specified thickness. The light fixtures installed in the unit must be of hazardous duty construction. The paint booth must be equipped with an automatic fire suppression system. Either sprinklers or dry chemical fire suppression will work. All doors must open outward from the booth and must be held closed by explosion venting latches. The booth must also feature explosion venting panels throughout the unit to keep debris from flying and endangering personnel or property in the event of an explosion.
Various Airflow Paint Booth Designs
Paint Booth Air Flow designs have evolved over the years.
Paint Booths started as Crossflows. This is a booth that has its air pulled across the article that is being painted. The majority of this design was characterized by the air traveling the long dimension of the spray booth. Filters we put in the main product doors and the exhaust filters were in a plenum in the back wall. The next variation came in a crossflow booth called a Reverse Flow Paint Booth. As crossflow booths aged their door seals would start to crack and flake away. If this problem wasn’t immediately serviced dirt could be drawn by those seals and end up on the procuts being painted. The Reverse flow simply put the exhaust in the front of the booth on either side of the product doors so that any dirt that was drawn into the booth that got by a leaking seal would be taken straight into the exhaust filters. The intake filters were in the back wall of the booth in a ridgid frame.
As the industry matured it was found that the best paint work came from the shortest dimension the overspray would have to travel over the product to get to the exhaust filters. This is desirable because if the overspray is left to settle back down on the painted surface it can show up like a bit of dirt. That is then referred to as a blemish. When painting cars for example the shortest distance is generally from the top to the bottom of the car. This is where the downdraft paint booth came from. A pit is cut in the floor. Filters are placed beneath grates in that pit and the exhaust air is drawn there. A pit is a costly investment. Some companies that are in rented facilities have difficulties cutting their floor to install a pit so other paint booths were developed to answer that need. The semi-downdraft is a booth where the air comes into the booth on the ceiling in the front of the booth and exhausts low on the back wall. This is close to the way a cross draft works but the air is moving in a downward direction which is where the name semi-downdraft comes from. The Side Down draft is another type of down draft paint booth. This also does not have a pit. The exhaust system runs down both side walls and the filters are at the bottom of those walls.
Final Design Thoughts
In conclusion, paint booth design and quality plays a crucial role in the safe operation of spraying flammable and potentially explosive chemicals. Reach out to us at Spray-Tech to learn about our line of paint booths and accessories.