Nerdgasm: Magnehelic installed

[Ohio Mike]

Phil Thien said:

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Very nice. Now when people are in the shop you can walk up to it and tap it a few times with your finger. Say, "that can't be right, can it? This isn't good." Then advise everyone to get the heck out of the house.

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[Cian]

Miser -

Correction. I couldnt remember the name, but it was your pics that first got me interested in this idea. Thank you!

And it appears youre taking your readings on the high pressure side (similar to the Oneida kit). Obviously, I have mine on the low pressure side. Wonderful lil' gadget, eh?

[Ohio Mike]

Cian said:

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Miser -

Correction. I couldnt remember the name, but it was your pics that first got me interested in this idea. Thank you!

And it appears youre taking your readings on the high pressure side (similar to the Oneida kit). Obviously, I have mine on the low pressure side. Wonderful lil' gadget, eh?

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Now I'm confused (as usual)

It appears that Miser is measuring positive pressure just prior to the filter. Presumably an INCREASE in pressure means it's time to clean the filter.

It appears that Cian is measuring negative pressure (vacuum) on the intake of the dust collector. Presumably a DECREASE in negative pressure means it's time to clean the filter.

Does the same make and model gauge work for both applications?

Sorry I'm being so dense ..... I'm having trouble picturing this.

[fredhargis]

Yeah, Magnehelics measure both positive and negative pressure.. They have high and low pressure ports on the back, you just use the correct one. You can also use them to measure differential pressures, which takes both ports....

[Cian]

fredhargis said:

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Yeah, Magnehelics measure both positive and negative pressure.. They have high and low pressure ports on the back, you just use the correct one. You can also use them to measure differential pressures, which takes both ports....

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What Fred said. The gauge has two ports - both high and low pressure - depending on the application you have in mind. The gauge works via comparison of the pressure difference between these two ports. For me, I utilized the low pressure port to measure the vacuum pressure in my duct. The high pressure port (with no hose attached to it leading to anywhere) is registering the pressure in the ambient air of the shop. So in my case, the pressure in my DC duct is 8 inches variant from the pressure observed in the room.

Regarding high and low pressure in a DC system, just know that anything upstream of the fan blades is low pressure (being sucked toward the fan), and everything downstream would be high pressure (being pushed away from the fan). Obviously, my application seems very simple, but it's all that is needed to gauge (pun fully intended) the performance of my filter.

Not to confuse you, but as Fred noted, professional installers often use both ports to measure the specific drop across a given membrane as shown below.



If I come across another cheaply, I may do as such on my house HVAC system (vs diligently replacing the filter every 3 months - whether it needs it or not). Certainly over the top, but we are nerds after all.

Hope that helps.

EDIT: FWIW, that diagram above is the application which Miser has his deployed. He has his measuring the actual filter back pressure in (relation to ambient air pressure - hence no second tube). So whereas I would be looking for a vacuum drop from 8" down to maybe 6", he will be looking for an increase in back pressure from 1" to maybe 3". His is actually a more precise configuration than how mine is installed, but I opted to not drill a hole in my DC flange. I'll live with this for awhile but can always reposition down the road.

[Ohio Mike]

Ahhh. Two ports on the back of the gauge. I get it now.


Thanks guys.


Mike

[fredhargis]

I bought mine menaing to get a pitot tube to measure the actual CFM I was moving....the pitot tube uses the differential Cian explained (both ports). I never got around to buying the pitot tube (plus, making that measurement is some amount of work, taking several readings across the duct) so it wound up in service much like Miser's.

[Miser]

My thanks to Fred as well for the idea. Its a relatively cheap addition to take the guesswork out of cleaning. Much of it is common sense (as in the fines from running 200 ft of stock through the drum sander will nail performance) but with it I have confidence I keep the system running at its peak. Pretty important for us basement dwellers!

[Cian]

Ohio Mike said:

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Ahhh. Two ports on the back of the gauge. I get it now.

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Yup. Here's a decent pic of the backside. Dwyer really put some forethought into the design ("Magnehelic" is their trademark name btw). You can utilize ports off the side or out the back and they provide threaded caps for the ports you will not use.


Photo by www.maraindustrial.com

[Ohio Mike]

Great pic. That makes it very clear.


Thanks, Mike