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Discussion Starter #1
I am trying to build my own Magnehelic leak tester just for the fun of it and the experience. I have all of the necessary parts: Dwyer magnehelic gauge, Dwyer flowmeter, needle valve, aquarium air pump, tubing etc.

Can anyone help me with the routing of the air flow? I know that the same initial air pressure needs to be applied to the high pressure and low pressure sides of the gauge (via the instrument). Is there a Y adapter required that permits only a 1 way flow of air so the two pressures can't equalize before the gauge can read them? Also does the type of tubing make a difference? Any help will be appreciated.

John
 

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jbtsax said:
I am trying to build my own Magnehelic leak tester just for the fun of it and the experience. I have all of the necessary parts: Dwyer magnehelic gauge, Dwyer flowmeter, needle valve, aquarium air pump, tubing etc.

Can anyone help me with the routing of the air flow?

John
If I get a chance I will take a picture of the inside of mine for you tomorrow..

Joe B
 

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Discussion Starter #4
JButky said:
If I get a chance I will take a picture of the inside of mine for you tomorrow..

Joe B
Thanks Joe. I'm a bit hesitant to ask this question on Delphi, because someone posted there about making Mag machines to sell (undercutting J.L. Smith's price) and he got "eaten alive". I thought I'd take a chance on SOTW first.

John
 

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jbtsax said:
Thanks Joe. I'm a bit hesitant to ask this question on Delphi, because someone posted there about making Mag machines to sell (undercutting J.L. Smith's price) and he got "eaten alive". I thought I'd take a chance on SOTW first.

John
Check your SOTW email account...Link posted to the picture..

Joe B
 

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These are primarily for flutes, yes?? Don't see how they could work with a tapered instrument. What is the "Mag-" stand for? Are magnetic fields used? Don't really understand how these work...
 

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Discussion Starter #8
shmuelyosef said:
These are primarily for flutes, yes?? Don't see how they could work with a tapered instrument. What is the "Mag-" stand for? Are magnetic fields used? Don't really understand how these work...
Magnehelic is the name of the pressure gauge made by the Dwyer Company that these machines use. They work on the principle of measuring the difference in the air pressure applied into the instrument against the pressure lost through leaks.

This link gives more information: http://www.jlsmithco.com/pdf/236044.pdf

There are some techs who have found creative ways to use this tool in their sax repair. Hopefully one of them will chime in with more details.

John
 

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magnehelic® = Registered trade name for a diaphragm activated dial gauge that measures changes in air pressure.

"Don't really understand how these work..."

http://www.johnsherman.com/gauges/magnehelic.htm
http://www.dwyer-inst.co.uk/htdocs/PDFFILES/cat/pressure/2000_cat.pdf

It is nice the way the 'MAG' device quantifies the degree of leak, but I use an almost-as-effective machine that costs nothing. Everybody has one. The more one uses it, the better it gets, at doing the job. :)

Take a mouthful of air and gently (pressure must not blow pads open) 'squirt' (i.e. blocked throat) out that air by gradually moving the back of the tongue forward (opposite of sucking through a straw.) All those nerves in the tongue and mouth tell the brain how readily the air is leaking out of the instrument.

I agree that isolating sections of the instrument is a bit tricky with a conical bore like a sax has.
 

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Discussion Starter #10 (Edited)
Thanks to Joe's picture of how to connect the tubing, here is the finished product. I am trying a gauge that only goes up to 3 (since it was only $15 on E-Bay) instead of the one that goes to 10 inches of water that are sold commercially. It may be too sensitive for this application. I will just have to try it and see. Thanks Curt for your offer to help as well.
 

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Well done, JBT! It looks great.

Is 15" inches of water their maximum pressure?
That would seem a LOT less than what would be provided by the "balloon test".
 

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Isolating sections on the saxophone is tricky but at the same time very simple. I gave 2 clinics at the San Antonio NAPBIRT Convention in April on how to do this. I 'd be happy to send my clinic notes.

David
 

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Discussion Starter #13
wilsaxo said:
Isolating sections on the saxophone is tricky but at the same time very simple. I gave 2 clinics at the San Antonio NAPBIRT Convention in April on how to do this. I 'd be happy to send my clinic notes.
David
I already have the notes printed in the Conference Program. Do your clinic notes include any additional information? If they do I would like a copy. I didn't attend your clinic since I didn't have a Magnehelic at the time (dumb move on my part). My question is how on earth do you insert your plugs into the right spot inside the sax bore? It seems to me like this would be the difficult part of the operation.

I understand you have also tested the porosity of various pads with the mag machine. Have you done any experiments with how various treatments affect a pads porosity or maybe different sizes of resonators? This is an area of great interest to me at the present time.

John
 

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The conference notes were written in a way that I hoped would allow anyone reading them to be able to use the info without attending the clinic. Insertion is pretty easy because there is always a tone hole or bell opening below the area you wish to plug which is larger than the size of your plug. You will almost always need the keys off of the area below and the one above the area of your plug so that your fingers can have access to it for positioning. Side keys may also have to be off. I just use my fingers and a popsicle stick, or 2, to guide it into position. I also have use an expansion style plug on an eye bolt that I bring into position with a wooden dowel with a hook at the end for use when the keys are still on the horn.
View attachment 2622

After seeing Jim Schmidt's pad testers in Portland, I got home and made mine from copper pipe caps found at my local hardware store, by silver soldering on brass tubes and drilling out an opening in the cap and leveling the test surface. You don't need a mag to use these. You can use suction or Gordon's "natural" mag described above.
View attachment 2620

I started testing every pad I had available and freaked when I saw the results of testing the popular untreated, anti- sticking pad with the great firm felt and strong cushiony skin that I was using on a Martin alto overhaul already in progress. I started in right away on testing treatments, many with airtight success. What I settled on with this pad was to disassemble it and place a very thin plastic film between the skin and felt. This way I kept all of the properties that I loved of the skin and felt while eliminating the one that I was uncomfortable with. The pad testing is important even if you are not trying for perfect airtightness. If the pad tests at "4" due to porosity, you just use this as your reference and do your work to "4", as any higher reading would indicate a coverage leak. The section you are working can all be brought to "4". After all, the jury is still out on porosity leaks from the player's perspective.

Hope this helps.

David
 

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Just trying to resurrect this thread a bit, I just recieved to day from JL Smith a mag machine.
I purchased it to quantify my jobs prior to letting them go out the door, for warranty concerns
First up wow, talk about sensitive, I thought I was doing a good job, but the unit showed me I was only doing an average job, example a clarinet that was going out the door read 2.1 fully assembled on the machine, it played nice for an older instrument. I put the extra effort in and fine tuned everything and managed to get the unit down to .7 reading, it played good still maybe a little better, but thats a hard call because I was looking for an improvement in sound, whether the extra work is really justified to achieve this result is an unknown to me yet, maybe might be worth it for a student who struggles to start with but for an experienced player they probably wouldnt notice the added results.
My question is, what do others out there that have this use as there bench mark. Clearly it impossible to read a zero.
Second question aimed at everyone, whats your thoughts on immersing a lightly pressurised clarinet or instrument in water, will it stuff the pads, damage the instrument, thoughts, ideas

Thanks
Steve
 

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simso said:
Second question aimed at everyone, whats your thoughts on immersing a lightly pressurised clarinet or instrument in water, will it stuff the pads, damage the instrument, thoughts, ideas

Thanks
Steve
For the sole reason the screws are going to rust up even on a plastic clarinet I would suggest not doing this Steve. For starters..
 

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Discussion Starter #17
Steve, thanks for reviving this thread. An update on my home made mag is that the gauge that went only to 3 inches of water was unsuitable, and so I replaced it with a gauge that goes to 10 like the commercial Mags have.

I am still in the learning stage with mine, but here are some observations at this point in time.

-Setting the open pressure to 4 as J Butky recommends seems to work well for flutes and clarinets.
-Valentino pads on plastic clarinets and piccolos will give a reading approaching zero.
-Bladder pads on plastic body clarinets a 1 reading is possible for each joint tested separately.
-Bladder pads on flutes a 1.5 - 2 is a typical reading for me.
-Bladder pads on older wooden clarinets can really vary depending on the condition of the toneholes
-Valentino pads on older wooden clarinets typically give a lower reading than bladder pads but readings also vary with tonehole condition

I am finding the Mag especially useful when doing repads testing each pad as it is installed by using rubber stoppers in the toneholes. I also would appreciate some feedback from those with more experience as well to see if my results are typical.

John
 

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Do those figures have a unit associated with them, such as cc/sec air leak?
 

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Discussion Starter #20
Doug is correct in that the measurement is in inches of water. The magnehelic measures differential pressure, comparing the absolute airtight side of the system to the one connected to the instrument.

Equal air pressure is split and sent to both sides of the gauge that are separated by a diaphragm. On one side the air goes directly to the gauge and on the other side the air goes to the gauge after passing through the instrument. If there is any leakage in the body of the instrument, the pressure will be less on that side and the diaphragm of the magnehelic will move its needle to show the difference.

The air pressure can be adjusted to up to 10 inches of water by the needle valve that controls the volume of air going from the pump to the gauge. The flow of the air is also controlled by the small flow meter up to a maximum of 1 scfh. J.L. Smith recommends setting the inches of water pressure to 8 and the flow to 1 scfh in his instructions. Joe Butky wrote that he gets good results by setting his Mag to 4 inches which has also been my experience.

Coltman in his experiment to test the porosity of pads made the observation that the maximum air pressure inside a woodwind when played is equal to roughly 1 inch of water. My assumption then is that 4 inches of pressure is adequate to test the spring closed pads, and that 8 inches of pressure is probably overkill.

The real value of the Mag so far in my experience is the ability to diagnose leaks quickly in clarinets and flutes. Adding more finger pressure or putting a piece of plastic under a pad quickly tells if that pad is the source of a leak.
 
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