Magnehelic choice

[WhiteSands]

Hello
between the 0 to 3 & -5 to 0 to 5 magnehelic which should I choose?
i prefer the 0 - 3 gauge but I am not sure if any manufacturer requires testing of exhaust valve using the negative part of the gauge?

 

[tbone1004]

are you DIYing or are you repairing for others?

If you're DIYing you can get away without one on and just testing the regulator. If you have Poseidons or other side exhausts you can actually test them in a bucket of water and get real damn close to what the mag gauges do and much faster. This is how Poseidon tunes them from the factory btw, they go on a mag for QAQC but they are rarely out of spec.

You can also DIY a mag gauge, they aren't particularly difficult to build and I think the Oxyhacker book has plans for one and I think there are threads on here with the same.

If you're buying one, buy the 0 to 3. It's more accurate and since you can't actually adjust exhalation resistance, there's no point in having it other than because you want it.

 

[herman]

For most uses, the 0-3 is fine, there is no need for a 5 inch scale and the 0-3 has wider spaced divisions so it's easier to read accurately. Personally I have a 0-3 for general use and a 0-1.5 that I use when I am really tweaking a reg. I do a lot of experimentation so I want the finer scale so I can see minute changes. What you may not know about mags is they have 2 ports, a pressure port and a vacuum port so all you have to do to test exhaust pressure is to move the hose from the vacuum port to the pressure port. The 5-0-5 (or a better alternative the 3-0-3) is more convenient but since you can just move the hose, it's not necessary.

I will disagree with tbone a little ( sorry old buddy ) but you can at times modify the exhaust resistance of a second stage. You can compare new vs old exhaust valves, some times they do get a little stiff with age and on metal seconds you can tweak the metal to reduce or increase the exhaust pressure, not normal tech stuff but then again I have never been accused of being normal.

 

[tbone1004]

Herman, I know you can test it and tweak it, but it's not in the scheme of normal peoples adjustments. On double hoses I'm sure it is more critical, but for normal second stages you replace the exhaust valve when it stops sealing properly or is noticeably stiff, not something you muck with regularly....

also, beer next time I'm in raleigh, last few times I've been up you're off gallivanting...

 

[WhiteSands]

Thanks guys. Awesome tips as usual!

 

[herman]

Beer is always welcome.
By the way, mags come up on ebay all the time for $20ish so don't pay big bucks for one. If you are in need of a quick test gauge, manometers are very easy and cheap to build (<$5)....and are the calibration standard so they are inherently accurate plus they give you the +/- range of the 5-0-5 mag. I used one (and it's still on the bench)for a long time, mags are cooler and a little easier to read but not better so don't dismiss them.