What Is Air-to-Cloth Ratio and How Do I Calculate it?

There are several factors to consider when sizing your industrial dust collector, including facility space, application and particulate volume. Of course, the end-goal is to have an efficient industrial dust collector that keeps employees safe and your business running smoothly — but what other factors should you consider?

That’s where air-to-cloth ratio comes in. Also known as filter velocity, air-to-cloth ratio describes the amount of airflow passing through each square foot of filter media. A lower ratio means more filter media is available for a given amount of air, while a higher ratio means the same airflow is passing through less filter media.

The appropriate air-to-cloth ratio depends on the dust type, particulate concentration, application and collector design. Below, we explain how to calculate air-to-cloth ratio and why it matters when sizing an industrial dust collector.

What is air-to-cloth ratio?

Air-to-cloth ratio is the amount of airflow, measured in cubic feet per minute (CFM), passing through each square foot of filter media in a dust collector. Also called air-to-media ratio or filter velocity, it is calculated by dividing the system’s CFM by the total square feet of filter area.

The appropriate air-to-cloth ratio depends on the application and dust concentration. Applications with heavier particulate loading or source capture generally require a lower ratio, providing more filter media for the amount of air being filtered.

Using the right filter matters as well. Bag filters are commonly used for heavier dust, such as wood and grain dust, while cartridge filters are efficient for fine dust and lighter-loading applications such as welding, plasma cutting and laser cutting. Pleated cartridge filters provide a larger filtering surface area, allowing more filter media within a compact dust collector design.

How to calculate air-to-cloth ratio

To calculate air-to-cloth ratio for an A.C.T. dust collector, we take the amount of airflow (CFM) and divide it by the amount of filter area within that dust collector. For example, if a dust collector was moving 4,000 CFM and had 2,000 square feet of filter area, we could say that it had a 4,000-to-2,000 ratio. This can be simplified to a 2:1 air-to-cloth ratio.

Another example, this time on the lower ratio end, is if a dust collector was moving 2,000 CFM and had 2,000 square feet of filter media. Since they are the same number, the air-to-cloth ratio equals 1:1.

These calculations show why airflow alone does not determine dust collector size. Two systems moving the same amount of air can have different air-to-cloth ratios depending on the amount of filter media available.

Why is air-to-cloth ratio important for industrial dust collection?

Air-to-cloth ratio is one of the more important factors in determining how long a filter will last in a given application. Although there are many factors that come into play when determining filter life, air-to-cloth ratios can give good guidance when determining the size of the dust collector required for a given amount of air.

Our experts will help you determine the right air-to-cloth ratio when selecting an industrial dust collector so that you’re not overspending while ensuring you’re overpreparing. If air-to-cloth ratio is too high, meaning there’s not enough filter media for the airflow and volume of particulate your application is producing, dust will actually enter the filters faster than they can keep up with. This will result in frequent filter clogging and reduce the life of your filter.

In general, a lower air-to-cloth ratio can support longer filter life by providing more filter media for the required airflow. Applications such as laser cutting, blasting, metalworking and robotic welding require the ratio to be selected based on the type and concentration of particulate being collected. Running too high of an air-to-cloth ratio can contribute to frequent filter loading, higher differential pressure and shorter filter life.

A.C.T. Dust Collectors offers the ultimate in air filtration. Interested in learning more? Contact us today and our team will help you determine the best air-to-cloth ratio for bag and cartridge filters in your application.