DIY Magnehelic Gauge
- Thread starter RiverRat
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Charlie99
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Are you sure that's PSI and not "inches of water"?hoosier:
Typical cracking pressures are something like 1/2" or 1" of water. That's why you can also do a crude test of a reg by simpy starting to submerge it in a bowl of water, with the mouthpiece up and only air inside. When the diaphram gets and inch or so into the water, that it should start delivering air ---- unless it is an octo that you have set to a higher cracking pressure.
33' of saltwater = 1 atm = 14.7psi So you can see that 1" of water = 14.7/33/12 = about 0.037psi.
OP
The one I bought is rated 15 psi. But I would think you would not "draw" more than that anyway in normal usage. I bought the 0-3" guage as it seems perfect for my Apeks regs. You can also attach the hose to the high pressure side and test exhalation effort with the right atachment to the regs exhaust. So for those that are confused about PSI versus inches of water, the PSI rating is basically the max amount, in PSI, of pressure you want to run through the unit, not much. But drawing a breath of air through a reg doesn't draw much pressure in PSI. The "inches of water" is actually what you read on the guage. It's a vacuum measurement just like any other manometer or vacuum guage. This is with the hose connected to the "low" pressure port. I guess it really could be called a "negative pressure port" if you think about it. And the exhalation effort on the "high pressure port", well you could call that port "positive pressure" I guess. A reverse manometer if you will, not a vacuum, but positive pressure. For some applications the 5-0-5 etc. may be the better choice. I'm not sure but I think on those guages the needle can swing to either side depending on if you're measuring positive or negative pressure.
ChangeAgent
Contributor
Anybody?
Unfortunately the PDF link on how to DIY one no longer works. Can anybody post some drawings or the like as I want to build a Magnehelic Guage myself.
Thanks
Unfortunately the PDF link on how to DIY one no longer works. Can anybody post some drawings or the like as I want to build a Magnehelic Guage myself.
Thanks
ams511
Contributor
You can't build one yourself. The OP purchased a gauge from eBay and mounted it using sheet metal.
You can build a manometer with some plastic tubing and a ruler if you want.
Last edited:
ChangeAgent
Contributor
OK I build one with tubing.
question. The Apeks XTX200 manual states for the cracking pressure: + 1.0 - 1.5 H20 (2.5 - 3.7 mbar). How do I translate that to the ruler I used? does 2.5mbar mean 25mm on the ruler?
Love some help here.
question. The Apeks XTX200 manual states for the cracking pressure: + 1.0 - 1.5 H20 (2.5 - 3.7 mbar). How do I translate that to the ruler I used? does 2.5mbar mean 25mm on the ruler?
Love some help here.
Timothy Moran
Registered
Attached is a .pdf of my DIY Slanted U-Tube Manometer. It works well and is easy to use.
TJ Moran
TJ Moran
ChangeAgent
Contributor
Wow pretty cool Timothy. Of to the DIY shop tomorrow. The slanting is a good idea btw! Thanks for digging this out for me, very much appreciated!
Timothy Moran
Registered
If you decide to build one similar to mine, here's a few more suggestions:
1. The clear plastic tube is from a Tropical Fish Store. They use them for filter lines and whatever. I used about 5/16 ID just as sort of an educated guess. In other SB posts on the subject of u-tube manometers, posters said if the tube is too big in diameter, it makes for a slower response time and makes the water column "move sluggish." I just used some food coloring in the water.
2. Keep the 2 tubes (upper and lower) as close to parallel to each other as you can, and as close to 30 degrees from horizontal as you can. Variations will introduce inaccuracies. Probably not that critical, but, hey, why not make it as accurate as possible.
3. The scale I used came from a stationery supply store. A place like Staples should have them. It is called an engineers scale and is sort of 3-sided, and one of the edges is a snug fit in the slot in the vertical board so ti can slide along the upper tube and easily align the zero-point with the static water level. I used the scale with the inches divided into tenths.
It's user-friendly; if you spill out the water or accidentally blow it out, you can just refill it, reset the scale, and you're good to go.
TJ Moran
1. The clear plastic tube is from a Tropical Fish Store. They use them for filter lines and whatever. I used about 5/16 ID just as sort of an educated guess. In other SB posts on the subject of u-tube manometers, posters said if the tube is too big in diameter, it makes for a slower response time and makes the water column "move sluggish." I just used some food coloring in the water.
2. Keep the 2 tubes (upper and lower) as close to parallel to each other as you can, and as close to 30 degrees from horizontal as you can. Variations will introduce inaccuracies. Probably not that critical, but, hey, why not make it as accurate as possible.
3. The scale I used came from a stationery supply store. A place like Staples should have them. It is called an engineers scale and is sort of 3-sided, and one of the edges is a snug fit in the slot in the vertical board so ti can slide along the upper tube and easily align the zero-point with the static water level. I used the scale with the inches divided into tenths.
It's user-friendly; if you spill out the water or accidentally blow it out, you can just refill it, reset the scale, and you're good to go.
TJ Moran
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