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Old 30th January 2007, 09:13 PM   #1
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Question Ladegaard Arm Air Requirements ?

I realize the air source of choice for these arms is the lowley aquarium pump, but have any of you builders calculated the actual pressure (PSI) and volume (CFM) that works best ?

I'm looking at some DIY options and I need to know what my target is before I start construction.

I believe the volume can be ballparked using the pressure and total orifice size, so at a minimum it would be a real service to me (as well as anyone else interested) if someone has actually measured the air pressure to post it here.

Thanx in advance,
Casey
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Old 30th January 2007, 11:45 PM   #2
kevinkr is offline kevinkr  United States
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Hi Casey,
I don't have one of these arms so I can't answer your question, but I do have an aquarium that lives in the room next to our master bedroom and both my wife and I are very light sleepers. We've had a lot of pumps over the last few years and the French made Rena is by far the quietest of the lot.. Might save you some trouble if you are going to use an aquarium air pump for this purpose.
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Old 31st January 2007, 12:54 AM   #3
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Hi Kevin-

Quote:
Might save you some trouble if you are going to use an aquarium air pump for this purpose.
If I do end up going aquarium, this info will certainly be of value

However, I have been thinking about the supply options for a while now, and I really think a Tesla Turbine Pump would be the bees knees . I figure a 5"-6" disc stack (cd-roms) 10-20 deep spinning 2-4K rpm would do nicely. Actually, a pump of these diminsions would have a peak output at 10X these speeds, and blow the arm across the room. The idea here is to have the pump lumbering along very quietly. I've seen a report on a unit this size being ran as a turbine that ran 15K rpm with a 65psi@4.5 CFM air supply..it worked out to be around 30% efficient if I recall. Going the other way with some napkin math, 15K rpm in would give approx. 20 psi@1.5 cfm..way to much!! Probably about right though at the "idle" speed I'm looking at.

This is all guess work until I know my target, and actually build one.

-Casey
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Old 31st January 2007, 03:00 AM   #4
kevinkr is offline kevinkr  United States
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Interesting, I wonder though how well it would work with air which is presumably a low viscosity fluid?

I will admit to doing the Tesla turbine thing routinely with my pizza cutter when doing the dishes... It's amazing how fast you can get it going if you orient it correctly relative to the water flow.. Perhaps this is more of an ersatz version of the Tesla, as water generally impinges only about 25 % of the surface area when I do it..

Sounds like an interesting project, and if anyone can get it to work I'm sure it will be you.. Presumably it would be as loud as a bunch of cds running at about 10 - 12X or a bit less?
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Old 31st January 2007, 03:38 AM   #5
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Quote:
Interesting, I wonder though how well it would work with air which is presumably a low viscosity fluid?
According to Mr. Tesla, and his modern followers, extremely well. The working models I have seen online use compressed air to drive them, and the original turbine was designed to run on steam, and as a pump, the "fluid" can be anything. The key is to space the discs slightly narrower than the thickness of the boundry layer of the medium you want to use. The main difference between pump and turbine is the shape of the cutouts in the center. As a turbine this is the exhaust, and are simple slots. As a pump this is the inlet, and will work with just slots, but works better when they are involute.

Quote:
Presumably it would be as loud as a bunch of cds running at about 10 - 12X or a bit less?
Potentially much less. Most of the noise of a cd drive is vibration from a slightly out of balance disc on a loose mount (spindle). Properly balanced, the only thing you should hear is the motor.

Noise is the motivation behind my consideration here. Not just the airbourn variety. Compressors basically come in three flavors, reed (aquarium pump), rotary, or piston/valve..all of them make a racket, and "pulse" the air. This pulsation has to be filtered, and just like a mains supply, it never goes completely away. If I can get a Tesla tuned right, it would be the equivalent of a "DC" air source. Instead of a mechanical regulator, pressure would be controlled by speed, and since it is only compressing as much as the arm needs, it wouldn't need a dryer.

I may be full of baloney, but the idea is intriguing enough to investigate it further.

-Casey
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Old 31st January 2007, 04:22 AM   #6
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Poking around for info, I found this site of a guy who built a turbine out of AOL discs . It's in Dutch so you'll need the fish in your ear.

Just think of running it backwards as a compressor.

-Casey
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Old 31st January 2007, 08:01 AM   #7
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cant tell you how much air you need, but its not alot.

The pump i'm using pumps 500lph, and im sure its under 1psi.
Mine is vaiable and i can use it on the lowest setting which must at least half the output.
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Old 31st January 2007, 12:44 PM   #8
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Hi graeme uk,

Thanx for the response..thats the kind of info I'm looking for.

Quote:
The pump i'm using pumps 500lph, and im sure its under 1psi.
That certainly answers the air volume question..500lph works out to .29 CFM (a number my Yank brain can visualize). The PSI sounds reasonable as well.

Sounds like even a really crappy implementation of Tesla's pump could clear this bar.

I guess I'll have to scab one together and see. As you can see from the above link, it wouldn't be a huge undertaking . The biggest challenge would be a quiet drive, I'm thinking a BLDC with a variable speed control with a piezo pressure sensor in the feedback.

-Casey
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Old 31st January 2007, 02:10 PM   #9
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the supply doesnt need to be smooth either as a smoothing tank can always be used. Im using a ballcock, just because it was the cheapest solid walled air tight thing i could find.
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Old 31st January 2007, 07:35 PM   #10
maxro is offline maxro  Canada
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Quote:
Originally posted by graeme uk
Im using a ballcock, just because it was the cheapest solid walled air tight thing i could find.
Cheaper than a 2 litre pop bottle?
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