What is the purpose of a magnehelic gauge? (On an AER Control Systems Unit)

AER Control Systems installs either a magnehelic or mini-helic gauge on just about all of their units so the customer knows when to clean or replace the filters.  These gauges are round, 5” in diameter for the Magnehelic and 3” in diameter for the mini-helic.  These gauges are mounted on the side of the AER Control Units, but could be difficult to see from the ground.  If you can see the needle and the numbers on the guage then that is a good start.

The function of a magnehelic guage is to measure the static pressure, it has two inlet ports a low side (minus) and high side (plus).  On air filtration units these gauges are located on the suction side of the blower; the airflow is being drawn into the blower inlet so the lowest static pressure is the port that is closest to the fan inlet as this is the most negative or lowest static pressure reading.  The dirty side of the filter is the high side or plus side and is reading the higher static pressure.  The reason why we use the magnehelic gauge on our units is to sense the change in pressure drop across the filters that AER Control Systems uses in their units.

Why would you want to know the change in pressure drop?  This is the one indicator of when the filters are becoming dirty, the higher the reading the more the pressure drop is across the filters.  With clean filters in the unit the magnehelic guage reading will be very low, somewhere between zero and one is a good rule of thumb, although this could be higher if the airflow is higher, the higher the airflow or air velocity going through the filters the higher the clean filter pressure drop.  As the filters become dirty the air velocity and airflow will begin to drop due to restrictions in the filter because of the dirt but the blower is trying to move a higher airflow and becomes stronger so the difference between the low side and high side increases.

How will I know when to clean or change my filters?  The first time your filters become dirty you will have to keep a close eye on the design airflow, as the design airflow drops, the guage reading will raise.  When the design airflow drops too much you will notice the collector is not performing as it should, the suction strength is not there, and you see more particulate filling up your shop.  This is the point at which you should clean or replace your filters, but before you do that place a mark on the face of the guage with a Sharpie or something similar at the needle reading so next time when the needle reaches this mark you will know by looking at the guage that the filters need to be changed.

Where do I purchase filters?  You can purchase filters at AER Filter Sales (203-239-0340 or www.aerfiltersales.com) color palette.

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