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Blow air at the dancers

Discussion in 'Special Effects' started by Grog12, Oct 8, 2008.

  1. Grog12

    Grog12 CBMod CB Mods Premium Member

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    So here's the effect I'm going for...and by I, I mean my Artistic Director. We need to blow air through hoses at dancers. At least two hoses preferably 4. The easy answer, an air compressor, is well...loud. And if we rent one, I'm a little worried about there being oil in the line. So either I need a quiet/clean air compressor, or I need another option.
     
  2. Pip

    Pip Active Member

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    What effect are you trying to achieve with this air? Why does it need to be through hoses?

    Independent from those questions:

    Just get a longer stretch of air hose so you can put the compressor in a place where you can't hear it.

    Thing is, even so - the air escaping a high pressure hose like that'll also be loud... Hence my questions about what you're going for here.
     
  3. Grog12

    Grog12 CBMod CB Mods Premium Member

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    Uhm...just what it sounds like....dancers holding hoses blowing air on other dancers so their hair and clothes blow in the wind.

    Very industrial/post modern feel to the piece.

    Air escaping the hose can be drowned out by the music (it is called Rock Ballets) The compressor cannot.
     
  4. propmonkey

    propmonkey Well-Known Member

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    also becareful as stray objects may get in the air stream such as rust, sawdust, etc.
     
  5. Pip

    Pip Active Member

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    Oh okay, I wasn't picturing the air hoses as visible to the audience. Yeah, if that's the case, I would say probably the easiest way to do this would be put the air compressor as far away as need be. That'd probably be way cheaper than trying to find a quiet compressor. All you'd need to get would be more hose to extend your maximum distance from the compressor.
    How long do they need to be blowing air?
     
  6. sk8rsdad

    sk8rsdad Well-Known Member Premium Member Fight Leukemia

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    Watch the air pressure and proximity to skin. It would be a "Really Bad Idea" (TM) to cause an air embolism. It messes up the choreography when a dancer drops dead on stage.
     
  7. Les

    Les Well-Known Member

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    [user]sk8rsdad[/user] is very correct!

    Aside from an air compressor, have you given any thought to just using air tanks that can be charged with 'x' amount of PSI per performance? It would depend on how strong and constant the air stream would have to be, but this would be the quietest option.

    portable air tank : Grainger Industrial Supply

    I know we have them at Lowe's but I couldn't find them online.
     
  8. Pip

    Pip Active Member

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    Yeahhh I guess I was imagining them not being too close to each other :p
     
  9. jwl868

    jwl868 Active Member

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    By hose, do you mean small diameter, like a garden hose or an air hose for a jack hammer, or do you mean large diameter, like a dryer hose?

    And are you looking for large volumes of air, or relatively small streams?

    How long does it have to last? - a large cylinder of compressed breathing-quality air may work.

    I was also thinking of a small industrial blower/fan (not a compressor). These put out alot of air at a low pressure - but they also generate alot of noise.

    A large diameter wand/nozzle may be needed to slow the air velocity down. There is something about directing a high velocity air stream at someone's face that bothers me about this.

    Joe
     
  10. Grog12

    Grog12 CBMod CB Mods Premium Member

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    jwl- By Hose I mean around the size of typical compressor hoses. I agree, as does my AD, about the air stream at someone's face/debris ect. Currently I think the suggestion of compressed breathing air is the way to rock and roll. I'm going to do a little more research into that and see what I can come up with. It also gives him another piece of the puzzle to play with.
     
  11. jwl868

    jwl868 Active Member

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    I've been too busy to do any of the math, so I don't know how much "low pressure" (say 10 psig) air that is in a typical cylinder. If you go that route, you'll need a pressure regulator so that pressure of the air that is coming out of the hose is already at a low pressure.

    Joe
     
  12. hsaunier

    hsaunier Active Member

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    Another concern to think about with high pressure air. Will the hose have some type of deadman trigger? If a high pressure hose gets loose, someone will get hurt when the snake goes wild and starts hissing at anyone close. Compressed breathing air presents many of the same problems. Dryer vent hose with a squarl cage fan might be an interesting thought (like an actual clothes dryer fan and motor). Quiet, High volumn air, Low pressure.
     
  13. jwl868

    jwl868 Active Member

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    I tracked down some information (and it was more difficult than I expected.)

    From what I can tell, the typical large compressed air cylinder is an "A"-type cylinder that has an actual volume of 1.76 cubic feet. When filled with compressed air, the cylinder pressure is about 2,400 psig. This works out to (2,400 + 14.7)/14.7 = 290 standard (that is, close to atmospheric) cubic feet of air. (This calculation also agrees with the generic term for this cylinder as holding 300 cubic feet of air.)

    What I can't estimate is the flow rate that you need. If you can manage with a flow rate on the order of 10 sfcm per hose, then the total requirement may be 40 to 50 scfm (for four hoses). With a 300 scf cylinder, that would only give you about 6 minutes of air. (I tried to find information on line that I could relate to , like a hand-held hair dryer and it appears that those put out 50 to 100 cfm, so my estimate may be too liberal.)

    Unless you can find a cheap way to test this, it may not be a very practical approach.

    Joe
     
  14. philhaney

    philhaney CBMod CB Mods

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    With a compressor sized hose you're going to get the same effect as the centrifuge scene in Moonraker, when you see the skin rippling on James Bond's face in the close ups.

    (Which is how they shot that scene. Roger Moore directed the air flow from an air hose at his own face and kept it just off camera.)
     
  15. Van

    Van CBMod CB Mods Premium Member

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    A large resivoir compressor, such as a 60 gallon shop tank should have plenty of capacity for a 2-3 minute dance, especially at a low pressure. Now, That being said there are a ton of safety issues here! Under no circumstances should an air flow from a compressed air line be directed at a persons face! The chances of an air embolism, while possible, are extremely extremely thin, unless the air nozzle is right up against the skin and over a large vein. I would run a coulpe of redundant in-line air dyers
    This will reduce the chance of any stray liquid reaching the end of the hose. You might want to consider building a Venturi type device for the end of the hose this will increase the volume, but decrease the pressure of the air actually heading towards the girls, this will, I think give you a better " Hair blowing in the wind" effect anyway. Look up Venturi or Venturi Effect and see if you can figure out a way to incorporate one on the end of the hose. If you get stuck I can draw you something pretty quick. I really can stress enough how very dangerous using high presssure air and pointing it at the face can be. Even a small particle of dust can scratch a cornea when accelerated enough. It hurts and can cause long term issues as well.
     

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