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Spark Gap design

 * Original msg to: Jbiehler-at-teleport-dot-com
 * Carbons sent to: usa-tesla-at-usa-dot-net

Quoting Jerry Biehler <jbiehler-at-TELEPORT.COM>:

> I was wondering if anone has tried making an air quenched spark
> gap by moving air throught the center of one of the sparkgap 
> electrodes. Here is a rough ASCII drawing...

        --------I   I------------I
        I       I   I            I---------
        I       I   I------------I---------
        I       I    <- Air <- <- <- <- <-
        I       I   I------------I---------
        I       I   I            I---------
        --------I   I------------I
            ^     ^     ^
            I    Gap    I
            I           I
       Electrode    Electrode

************************************************************

Good drawing. This exact gap goes all the way back to spark gap
radios. This same gap is pictured on page 84 of Duane Bylund's
book: MODERN TESLA COIL THEORY, Duane A. Bylund, 1990, Tesla Book
Co., no ISBN or Lib. of Congress No, paperback 142pp. Available
from Tesla bookdealers and the author: Duane A. Bylund, 140 S.
700 E., Spanish Fork, Utah 84660 USA.

I have a fair amount of experience running air blast gaps in the
multi-kilowatt range. I found my best design when I purchased
some solid brass utility door knobs at the hardware store and
drilled the backs all the way thru to the face (which was used
for the electrode surface). With two of these faced off and air
injected thru the face of both electrodes, I discovered some very
interesting effects.

Apparently the smooth curved surface of the electrode exhibits
some aerodynamic properties when high speed air is flowing over
it, much like an airplane wing. This causes a physical sheering
force which acts on the plasma channel and effectively quenches
the gap. Borrowing from your ASCII art work:  


              .-*           *-.       
             |    *       *    |      
        ------------*   *-------------- 
         -> Air ->         <- Air <-    
        ------------*   *--------------
             |    *       *    |
              '-*          *-' 
                      ^ 
                     GAP

What I am trying to show are a couple of small, solid brass,
utility door knobs available in most large hardware stores for
around $4.00 each. I did not show the flanges where these knobs
mount flush against the flat surface of the door. The center air
shaft is NOT drawn to scale, and in fact would be about the same
diameter are the pre-drilled and tapped holes used to mount the
knobs in their conventional applications. I just drill the
existing holes right on thru the face of the brass knob.

Another advantage to the curved surface: the gap breaks down
right near the air injection port. Turbulence and shear caused by
the air moving over the curved surfaces then forces the arc to
the edges of the electrode, which assists in quenching because
this is forcing the arc into the widest part of the gap. 

I have been very pleased with my test results of this design. The
gap seems to take advantage of several methods of quenching:
direct cooling from high speed air; wind shears and turbulence
(pressure changes) caused by high speed air moving over curved
surfaces; and the physical stretching of the arc as it moves into
the widest section of the gap.

Richard Quick


... If all else fails... Throw another megavolt across it!
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