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Author Topic: Need an air flow generating unit for automatic wind instrument  (Read 2681 times)
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Dubuque, Iowa, USA
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Wouldn't a decent sized centrifugal fan work for this? I thought recorders don't have all that much air resistance. In fact wikipedia mentions pipe organs use pressures in the order of 0.1 psi which equates to roughly 2.75 inch-aqua. I'm pretty sure even small centrifugal fans that were used in computers years ago can create static pressures higher than that.

The fan needs to be an impeller type and not squirrel cage. Even a ~250W furnace blower (which are squirrel cage) don't do anything for static pressure (DAMHIKT). You could use something like a vacuum cleaner motor or pool toy / mattress inflator but the problem is that they're too damn noisy.

To your question on CFM for a refrigerator compressor it looks like they're in the 1 CFM  (28 liter/minute) range and capable of ~100 PSI. Surprising number of examples of "homemade air compressors" on Youtube using these pumps. They are oil piston compressors just like typical large compressors so I suppose it does make sense.
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The fan needs to be an impeller type and not squirrel cage. Even a ~250W furnace blower (which are squirrel cage) don't do anything for static pressure (DAMHIKT).
I used to think that. A few years ago I hooked up a 100mm centrifugal fan to a high speed mini drill motor and passed the outflow through an 8mm orifice. We were levitating ping pong balls a good few feet above it. And the noise wasn't all that bad.

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To your question on CFM for a refrigerator compressor it looks like they're in the 1 CFM  (28 liter/minute) range and capable of ~100 PSI. Surprising number of examples of "homemade air compressors" on Youtube using these pumps. They are oil piston compressors just like typical large compressors so I suppose it does make sense.
I don't think 1 cfm will be enough. But if it was then you'd want to build a buffer tank to smooth out the oscillations. And if you're going to do that, then just buy a cheap 2hp compressor.

BTW, even these 2.4 W fans can pump 9.5 cfm with a static pressure of 6.5 inch-aqua. And only produce 32dBA.
http://www.jaycar.com.au/productView.asp?ID=YX2530
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Brisbane, Queensland
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Isn't the flow keeping the ping-pong balls aloft, not the pressure?  I have seen in vacuum cleaner shops where they have a beach ball hovering above their latest model cleaner.  I would think it would not require very much pressure at all, but a decent flow rate.

I'd be trying a compressor designed for airbrushing or spray tanning, they are usually quiet.

What about a CPAP machine?  One would think that it's capabilities would mimic those of a human's, due to the way they function.

Just ideas for you mate!

Ash

Edit, what about inflating a car tyre beforehand and using that as a cheap reservoir for the compressed air?  you would still need a regulator.
« Last Edit: November 21, 2012, 08:44:36 am by Ashduino » Logged

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Isn't the flow keeping the ping-pong balls aloft, not the pressure?  I have seen in vacuum cleaner shops where they have a beach ball hovering above their latest model cleaner.  I would think it would not require very much pressure at all, but a decent flow rate.
Sort of. Something has to create that high speed flow. And that is pressure. We were putting bits of blu-tack on it to make it spin and stuff. There's no way I could've made that ball stay floating with my lungs. Anyway I tried a 4.5 watt squirrel cage out of an old HP computer today. I had no recorder so made a ghetto one. It seems to work fine. Pretty sure this is more about decent flow rather than high pressure. It would be different if trying to play a trumpet or reed instrument.

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What about a CPAP machine?  One would think that it's capabilities would mimic those of a human's, due to the way they function.
That's a really good idea. The fixed pressure versions seem to put out enough pressure. The problem though is the cost. They're damn expensive.
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I will agree with those who have said that this is more about airflow than pressure.  I play clarinet and tenor sax, and I used to play the recorder.  Comparatively, the recorder takes basically no air pressure or volume.  A casual exhale is more than enough to get a sound on the recorder.  A good breath of air (3-5 L) could play the instrument for about a minute if not more.  What you will need to worry about is a very constant stream of air.  Any pressure spike could cause the recorder to over-blow and thus squeak. 

Don't discount the shaping of the air into the instrument either.  The recorder is less sensitive to this that most wind instruments, but the angle at which the air is introduced will affect the sound.   
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