Tech Tip: How to Use a Dwyer Magnehelic Differential Pressure Gage

The Magnehelic®, is a test instrument that has been around the HVAC industry for quite sometime.. It is used for measuring the static pressure of an HVAC system. 

How it Works

The magnehelic has a very sensitive diaphragm that responds to changes in pressure. When pressure is exerted on the diaphragm, the dial of the magnehelic responds accordingly and moves to the appropriate pressure. For this diaphragm to function correctly, positioning of the instrument is important. It must be level and in the vertical position when measuring pressure. If the magnehelic is in any position other than level and vertical, the diaphragm can sag and cause inaccurate readings.

Today, there are many options such as digital meters, and even blue tooth options. Check at Stromquist & Company to purchase these online.

Video Transcript

Hi Control Trends Community. This is Eric Stromquist with, your source for smart building in HVAC control news you can use. We get a lot of questions on the website about Magnehelic gauges and how they work. I think about it this way. The doctor checks your blood pressure for a reason because basically that pressure allows the blood to flow from your heart through your body. If you get a card, you got a problem — same thing with your buildings and same thing with your homes. If restrictions, like dirty air filters or other restrictions, keep the air from flowing, then you have to troubleshoot it because the tenants are not going to be happy. So how do you do this? Well, in this video I’m going to talk about the tried and true the Dwyer Magnehelic gauge. So check it out. So short video, watch it till the end.
If you like it, please subscribe to the Youtube Channel and give us a lot. Okay, so let’s look at the basic Magnehelic gauge and as you can see it’s a couple of things, just a set of magnets. It is a center that’s senses the differential pressure, the static pressure, and then it’s a helix that wind and unwind as the magnet is pulled from side to side. You can see how this works in this particular little video clip here. Okay? You can use these gauges and a lot of different ways. Typically what you’re going to use it for is to diagnose airflow problems, uh, in a unit. So to do that, you’d be putting a pitot tube or some soother type of airflow sensor in the supply return air streams. And the most important thing to remember is the pitot tube that must be inserted at 90 degrees and points into your air flow, if you get it backward, that’ll measure readings up.
Okay? So once you get the supply and the return hooked up, you are ready to go? You can either read it directly off of the specs of your equipment to get the differential pressure rating that the equipment will operate at optimally. If it’s not in that range, then you know you’ve got a problem. It could be dirty air flow filter, or something could be clogging up your duct work. Okay. Many, many uses of this. You can use it on your uh, AC units, your furnaces, you can use in commercial applications too, but it’s all based around the airflow pressure. You got to get the airflow through the system. Now Stromquist Company, styromquist.coim, we still stock Magnehelic gauges and even sell lots of the Dwyer Magnehelic gauges, because it is one of the all-time great differential pressure gauges and it still works well.
A lot of people have a popped over to the electronic ones, that we stock as well, and there are a couple of other great brands. The same principles apply, but now you get an electronic reading and can even use Bluetooth, and you can use your phone to do your diagnostics. Okay. So I will put some links, with some Magnehelic and electric meters in the notes below. So if you’re looking for a Magnehelic pressure gauge, click the links, take you right to website. All right, if you liked this video, please subscribe to our YouTube channel and give us a thumbs up. If you have any questions, reach out in comments.


9 Responses

  1. This youTube video had nothing whatsoever to do with using your gages. I wasted my time listening to it. It would have been a fine video, if it had been called How to mount a Magnehelic Gage.

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  3. This video has nothing to do on how to use the pressure gauge.Why not have an easy video on how to use it or how to install on system to check differential pressure instead of delibertly mislable the videos it is now.

  4. I agree, I wasted my time watching this video. Title was misleading! I wanted to learn the proper use of the gauge and if it would work with my application. Probably a little more important to push the function of the equipment first
    then mounting accessories…..?

  5. I agree Bodaciously. I watched the instruction then spent the next day rotating the tires on my ’91 Ford Futura. I highly recommend factory paint only when touching up the paint on your toro mower blades. Invest in dildo futures.

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