Defining Air Filtration Equipment

Designed for filtering ambient air contaminants, an air cleaner consists of a blower and disposable filters, and can collect only as much contaminant as the filters can hold (see also Dust Collector). An air cleaner is most effectively used in multiples in large rooms so that an air flow pattern is established to move the dirty air toward the filters.

Filtration velocity (also referred to as "face velocity"), normally expressed as flow of air in cubic feet per minute (fpm) divided by area of filtration media in square feet.

Designed to handle heavy dust loads, a dust collector consists of a blower, dust filter, a filter-cleaning system, and a dust receptacle or dust removal system (distinguished from air cleaners which utilize disposable filters to remove the dust).

Online Cleaning – automatically timed filter cleaning which allows for continuous, uninterrupted dust collector operation for heavy dust operations. Offline cleaning – filter cleaning accomplished during dust collector shut down. Practical whenever the dust loading in each dust collector cycle does not exceed the filter capacity. Allows for maximum effectiveness in dislodging and disposing of dust. On-demand cleaning – filter cleaning initiated automatically when the filter is fully loaded, as determined by a specified drop in pressure across the media surface. Reverse-Pulse/Reverse-Jet Cleaning – Filter cleaning method which delivers blasts of compressed air from the clean side of the filter to dislodge the accumulated dust cake. Impact/Rapper Cleaning – Filter cleaning method in which high-velocity compressed air forced through a flexible tube results in a random rapping of the filter to dislodge the dust cake. Especially effective when the dust is extremely fine or sticky.

Shaped inlet designed to capture contaminated air and direct it into the exhaust duct system. Design and orientation of the hood takes into account the type of dust generated, effects of gravity, and worker breathing zones.

Pressure equalizing chamber. In dust control systems, it generally supplies fresh air to replace contaminated air being removed for filtration.

Designing Industrial Ventilation Systems

Standard air is dry air at room temperature (70 degrees F) and sea level pressure. The density is about 0.075 pounds per cubic foot. Fans that move air that is warm or a high altitude should be sized to allow for lighter air.

The area in close proximity to a worker's head. An essential consideration in designing the dust removal system; the dust collector hood or inlet should always pull the contaminated air away from the workers face and never toward his or her face.

Motion that is a result of both differences in density as well as gravity. Can refer to natural circulation or intentional heat transmission utilizing natural principles.

In industrial ventilation, air movement created by a fan to control contaminated air.

Static Pressure – Potential pressure exerted in all directions by a fluid at rest; for fluid in motion, measured in a direction normal to the direction of flow. When dealing with air, static pressure is usually expressed in inches water gauge. Velocity Pressure – The kinetic pressure in the direction of flow that is necessary to cause a fluid at rest to flow at a given velocity. Usually expressed in inches water gauge. Total Pressure – The algebraic sum of the velocity pressure and the static pressure.

Air Horsepower – The theoretical energy required to produce air movement and pressure if a fan were operating at 100 percent efficiency. Brake Horsepower – Actual energy consumption of the fan motor.

Instrument that measures pressure; a U-shaped tube partially filled with a liquid (usually water, mercury, or a light oil) so that the amount of liquid displaced indicates how much pressure is being exerted on the instrument.

In ventilation terms, the volume of outdoor air supplied to a building to replace air being exhausted.

Amount of distance the air cleaner impacts air circulation pattern. Used to determine the number of air cleaners needed to clean a very large room.

Slot Velocity – Linear flow rate in feet per minute of contaminated air through slot. Capture Velocity – The air velocity required to pull the contaminants into a collector hood or duct system. Existing air patterns in a room such as an open door, an air conditioning discharge, or a cooling fan may have a substantial effect on this requirement. Conveying Velocity – Air velocity needed in horizontal ducting to prevent dust settling.

Describing Contaminants

Assemblage of small particles, solid or liquid, suspended in air, generally from 100 microns down to .01 micron, such as dust, fog, or smoke.

Small solid particles generally ranging in size from 1 mm (such as a grain of sand) down to submicron (fine, respirable contaminants).

One thousandth of a millimeter (millionth of a meter): approximately 1/25,000 of an inch. Submicron dust designates all particulate smaller than a micron.

Small suspended droplets of materials ordinarily liquid at normal temperature and pressure. Can affect operation of electronic equipment as well as the safety/comfort of the worker environment.

Air suspension (aerosol) of particles, normally but not always solid, formed from combustion or sublimation.