How to Know When to Change Spray Booth Filters

Q: How do I know when it’s time to change my spray booth filters?

A: When it comes to determining when to change your spray booth filters, first we have to differentiate between intake filters and exhaust filters. Intake filters are located where the outside or shop air is introduced to the spray booth working environment. These filters work to ensure that the air introduced into the spray booth is free from debris, which can cause defects in your coatings. Exhaust filters are possibly located in several different locations, depending on the design and construction of your spray booth. The primary function of these filters is to capture overspray from the booth working environment and prevent harmful and hazardous particulates from being exhausted into the atmosphere by the booth exhaust fans.

The function of both filter types is paramount to the spray booth functioning properly and ensuring the best possible coating finish. Spray booths are designed to meet National Standards, such as OSHA and the NFPA. When filter maintenance is neglected, the performance of the spray booth will fall below the standards’ requirements. When the spray booth performs below the designed parameters, proper airflow will not be present and the likelihood of overspray or dust to accumulate on the coated part increases exponentially.

 

 

Because there are many different filter constructions available, it is difficult to mandate a certain time interval for filter change outs. There many other factors that plays a part in the life span of the filters, including cleanliness of the surrounding environment, type of coating being sprayed, application styles and equipment used, spray booth air speed, spray booth design and construction and design of the filters can all affect the life of the filter.

However; there are some key indicators that your filters are coming to the end of their effective life span.

Intake Filters:

• When an increase in debris or dust is noticed in the booth or in the coatings
• If you have a manometer or Magnehelic gauge to measure pressure drop through the filter, change at the suggested loading of the manufacturer
• Filters have been installed for six months

Exhaust Filters:

• When overspray is noticed to be lingering in the booth more than usual
• The spray booth fan is operating at 100% capacity
• If you have a manometer or Magnehelic gauge to measure pressure drop through the filter, change at the suggested loading of the manufacturer
• Applying a coating that is capable of spontaneous combustion or other harmful compounds
• Filters have been installed for one month

It is best practice to establish a filter maintenance program with the help of your spray booth manufacturer or your filter provider. Improper filter maintenance can affect more than just the finished coating. It can also affect the health and safety of your employees as well as the profitability of your business.

Q: We run a two-shift operation (16 hours) and it takes 45 minutes every time we change them out. We are currently using a polyester roll media and apply a two-component prime and topcoat system. Filters are changed following the manufacture’s specification of 0.5” WC on the booth-mounted manometer.

A: Normal is very difficult to define when it comes to determining interval for filter change out. This question is similar to the previous one in this article and has some parallels. In your case, you know when to change out the filters based on the manometer reading. For your situation, the real question may be “am I using the right filter media?”

There are many factors that impact filter life, including type of coating, application equipment, spray technique, spray booth design, air flow and filter media type. Spray booth exhaust filters are available in a wide range of compositions, including slit and expanded paper, cardboard, fiberglass, polyester and combinations of these materials. Many people tend to use the booth filters supplied with the spray booth from the manufacturer. In many cases, these filters will function well across a wide variety of coatings and manufacturing processes. For higher volume manufacturers, such as yourself, it is recommended to reach out to the booth/filter manufacturers to ensure that the filter is optimized for the process.

Spray booth exhaust filters are typically characterized by the capture efficiency, pressure drop and holding capacity. Per code, the particulate capture efficiency must be greater than 98%. Ideally the pressure drop will lower as the filter loads and, in regard to holding capacity, typically more is better. All filter manufacturers can provide this information and it serves as a method to guide in the selection process.

All filter media available can work across a wide range of applications. However, in some cases, it may not be optimal for certain applications. One of the characteristics of polyester filtration products is the tendency to face load with faster drying coatings. I suggest evaluating a high-capacity filter constructed of slit and expanded paper with a polyester backing. The multilayer expanded paper portion of the filter will perform as a baffle system and collect the bulk of the overspray. The polyester backing will then collect the smaller, dryer particulate. I would expect that the expanded paper and polyester style filter would extend your filter life by a factor of 3-4X. Ultimately, running an online trial at your facility is the best way to identify the proper filtration product for your specific combination of conditions.

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Trey Peavy is product manager for Col-Met Engineered Finishing Solutions. Visit colmetsb.com.