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  #1  
Old 11-08-2013, 01:53 PM
Paul B Paul B is offline
 
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Default Airspeed Indicator broken?

I have an airspeed indicator in my hand, not connected to anything. I can blow into the AI's pitot port and quickly bring the indicated airspeed up to any value I want. When I quit blowing into the AI, the needle very slowly goes back to 0. It takes 60 seconds for the needle to go from 120mph indicated to 0 with both pitot and static ports open. Is this normal or does the AI likely need repair?
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  #2  
Old 11-08-2013, 04:07 PM
flyinga flyinga is offline
 
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There is a small needle-type valve in the AS pitot input that can be adjusted to change the rate at which airspeed can change. Usually can be done with a small screwdriver. In too much and the airspeed changes too slowly (like yours); out too much and the airspeed will "bounce" around in unstable conditions.
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  #3  
Old 11-08-2013, 04:55 PM
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And for anyone else reading this thread; NEVER blow into an ASI.
If you want to operate it by mouth, apply suction to the static port.
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  #4  
Old 11-08-2013, 05:54 PM
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Sam Buchanan Sam Buchanan is offline
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Quote:
Originally Posted by Paul B View Post
I have an airspeed indicator in my hand, not connected to anything. I can blow into the AI's pitot port and quickly bring the indicated airspeed up to any value I want. When I quit blowing into the AI, the needle very slowly goes back to 0. It takes 60 seconds for the needle to go from 120mph indicated to 0 with both pitot and static ports open. Is this normal or does the AI likely need repair?
Quote:
Originally Posted by Mel View Post
And for anyone else reading this thread; NEVER blow into an ASI.
If you want to operate it by mouth, apply suction to the static port.
It probably needs repair now......
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Old 11-08-2013, 09:11 PM
krw5927 krw5927 is offline
 
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Quote:
Originally Posted by Mel View Post
And for anyone else reading this thread; NEVER blow into an ASI.
If you want to operate it by mouth, apply suction to the static port.
I haven't ever done this but can you tell us more about why blowing into the ASI is a bad thing? My first thoughts are this is exactly what the pitot tube does.

Is it the speed and force with which one could possibly peg the needle if they were not used to how much pressure it takes?

Thanks Mel, always learn something from you.
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  #6  
Old 11-09-2013, 06:24 AM
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The ASI is very sensitive to force and speed of the "blowing" and the moisture of breath.
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  #7  
Old 11-09-2013, 08:51 AM
Paul B Paul B is offline
 
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Default Thanks for responding!

I am always grateful for the collective wisdom at this site and the eagerness to share it. It sounds like I may have damaged the airspeed indicator by blowing into it (I only did this about 100 times), if it wasn't already broken. Can anyone recommend a place I could send this instrument to get checked out and possibly repaired?
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  #8  
Old 11-10-2013, 05:21 AM
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pierre smith pierre smith is offline
 
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A rubber squeeze bulb and a length of hose attached, can be used more gently while you're watching the needle move.

Best,
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  #9  
Old 11-10-2013, 09:56 AM
gasman gasman is offline
 
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A large syringe works well and has good control when testing for leaks or to compare markings on gauge with a manometer.
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