DIY Magnehelic Gauge

[Timothy Moran]

If you're interested, here's some numbers from my u-tube manometer for some of my fleet of regs.
Also has a lot of extra miscellaneous info which you can ignore.

TJ Moran

View attachment Inhalation Checks.pdf

 

[ams511]

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.

I have a magnahelic, you can find them cheap ($20 to $25) on eBay. However from what I remember from Harlow's book, you read the difference between the two water columns. As an alternative you can put a ruler in the sink and submerge the second stage slowly. It should crack when the diaphragm is submerged 1 to 1.5 inches in the water. Apeks has a flash presentation on this that is floating around on the web.

 

[ChangeAgent]

If you're interested, here's some numbers from my u-tube manometer for some of my fleet of regs.
Also has a lot of extra miscellaneous info which you can ignore.

TJ Moran

Interesting, I dive Apeks myself, still fun. Thanks for all the effort, appreciated!

---------- Post added June 1st, 2015 at 06:40 AM ----------

I have a magnahelic, you can find them cheap ($20 to $25) on eBay. However from what I remember from Harlow's book, you read the difference between the two water columns. As an alternative you can put a ruler in the sink and submerge the second stage slowly. It should crack when the diaphragm is submerged 1 to 1.5 inches in the water. Apeks has a flash presentation on this that is floating around on the web.

Thanks, I look for the presentation. Sink is a good tip.

 

[cmas3]

Apeks has a flash presentation on this that is floating around on the web.

hello, i don´t found this presentation, can you give me a web link

 

[lucca brassi]

magnehelic gauges looks like dinosaur in comparison with modern sensors.

 

[RobinC.]

What is the point about having the tube slanted vs on a vertical axis ?

 

[Timothy Moran]

A U-tube manometer works by measuring the difference between the 2 water columns. On the reg inhale side tube, the water rises with less pressure as you inhale on the reg. On the open-to-the-atmosphere side tube, it falls the same amount as the inhale side tube rises. Thus if you start with a scale along the inhale side tube, and you measure .5 inches of water when the reg cracks open, the difference between the 2 water columns will be 2 times .5, or 1.0 inches of water. If you slant the tubes at 30 degrees, the math (trigonometry) will show that the scale will now directly read the height difference between the 2 water columns. In other words, when you show a reading of .5 inches of water, it will be the actual inhalation cracking pressure, and you don't have to multiply it by 2. The 30 degree slant also has the advantage of expanding the scale which enables you to read the the column height a little more accurately. A couple of nice features of the slanted u-tube manometer are (1.) It requires no calibration. If you can accurately measure the water column difference, it is what it is. (2.) The readings are very repeatable. (3.) It's pretty "bulletproof." If you blow or suck the water out, just refill it, add a couple of drops of food coloring, and you're up and running again.
TJ Moran

 

[lucca brassi]

why so simple , it must be complicated !!!