Magnehelic gauge

[Tim Goins]

Thanks to all who helped me figure out that my filters were clogged on my Bill Pentz cyclone dust collection. I have done some research and also have followed the advice on this forum and I got a Magnehelic meter, to tell me when I need to clean my filters. My question is how is it hooked up? It has two ports on the back. A high and a low. Which one do I plug and which one do I use? It is a Dywer model 2020 PSI 15. I have the Bill Pentz design with the Wynn filters stacked. Do I tap into the clean out box or what. Help!

[Dick Mahany]

Here's a link to the manual: http://www.dwyer-inst.com/PDF_files/A_27_low.pdf and has instructions for the connection. On my cyclone, I placed the static pressure tip in the duct between the impeller housing and the filters. Nothing complicated. Good luck. I use a 0-5" gauge for my filter. Clean whenever it gets to 3".

[John Aspinall]

Don't plug either port. You are measuring a difference in pressure. (Often called a drop in pressure.) Even if it's a difference between some place in the ducts, and plain ol' atmospheric pressure in your shop, there are two pressures. One pressure at each port.

[Jim German]

You'll probably want a different Magnehelic. Most dust collectors run at a few inches of water, probably won't even show up on a 15 psi gauge.

[Ole Anderson]

I went with the 0-5 in gauge for my filters, left one port open to the atmosphere and used the barbs supplied and tapped into the duct between the filter and the cyclone. Trial and error will quickly tell you which port to use.

My 0-15 in gage for the cyclone performance quit working, tube is not clogged and is hooked up, need to do more troubleshooting.

[Tom Stenzel]

According to my Dwyer catalog the model 2020 differential pressure gauge is rated for 0-20 inches of water column. I don't think the 2000 series goes to 15 psi. Look at the scale on the gauge and see what you have. If you're trying to use it for measuring 0-5" of drop it wouldn't be my first choice (0-10" or 0-15" would have been better) but it should work well enough as is.

Pressure in inches of water column is a much lower unit of pressure than PSI. 1" of water column is equal to 0.036 PSI. That's why Jim said that a PSI gauge wouldn't work. A plugged filter wouldn't make a 15 PSI gauge budge at all.

To connect the gauge the high side connection is connected to the upstream side of the filter, and the low side connection is connected downstream of the filter. Then you are measuring the pressure drop across the filter.

Hope this helps,

Tom Stenzel

[Jim Neeley]

The gauge with high and low ports is a "differential pressure" gauge. The concept is that you connect the high port to the area with higher pressure and the low to the lower pressure. It's like the polarity of a battery.

If you are trying to measure the pressure drop across your filters, the high pressure area is downstream of the fan up to the inside the filter. Connect the high port to a convenient spot along that duct or into the fan. The low pressure area is your room, so you just leave that one open to the atmosphere.

If you wanted to measure the maximum suction of your DC you would hook the low to the suction-side of the DC and leave the high open to where the air is coming from: the room.

I've seen posts from people mounting their DC in an enclosure how large of a return vent they need and I've responded that it depends on how much of a pressure drop you want between the enclosure and the room (low is good). A magnehelic would be a good tool for assessing how much pressure you are losing getting the air out of the enclosure.

Take the example of someone who has 2" of pressure drop across their filters when clean and they then clean them when it reaches 3" (no enclosure). Assume after putting it in the enclosure there's q" of pressure drop between the inside and outside of the enclosure. In that case the DC will perform the same way with clean filters in the enclosure (2" + 1"=3") as it did before when the filter was dirty (3").

What's too much is your judgement but I'd propose that you want the drop to be a small percentage of the difference between dirty and clean filters. Otherwise you'll be cleaning your filters too often due to the total pressure drop.

In this scenario, the high is the inside of the enclosure and the low the outside. If you are going to buy a Magnehelic it'd be a good baseline test.

Jim in Alaska

[Michael W. Clark]

The 2020 is a 0-20"wg gauge. The 15 psig is a mechanical (structural) rating of the housing.