This gap offers several advantages over many of the gaps I have
studied. It frees the coil up from any electrical utility required
when fans or blowers are used on a static gap. This is also true
when a rotary gap system has been used with a neon transformer
power supply, as this gap can replace a rotary in this application
and give better performance. This gap has very high Q and gives
extremely low quench times. The performance of this gap on coils
powered by neon sign transformers is second to none. If you run
neons, and you want the longest spark at any cost, then this is the
gap for you.

The system consists of two electrodes cut from 1 inch brass bar
stock. The electrodes are 1-1/2 inches long by 1 inch diameter. 
The back side is machined one inch deep to accept a 3/8 inch
threaded brass dowel. The face of the electrodes are flat and
polished. The electrodes weigh 4 & 3/4 ounces each and sink a lot
of heat without requiring cooling fins. Beneath the gap, I mounted
a 1/2" ID pipe fitted with a standard male air coupling at one end.
I hook the air feed pipe to a two-stage piston air compressor, and
using a regulator, blow 20 psi (minimum) of air through the gap
electrodes from the bottom up. It quenches extremely well.

With the arc shielded during operation, the compressed air blows a
clearly visible jet of hot ions upwards from between the gap. The
flame extends one to two inches high. Even after 15 minutes of
operation at 2 kw, the electrodes are barely warm to the touch.

This configuration offers several advantages: 

(1) Gap distance can be adjusted precisely and quickly by rotating
the electrodes on the threaded rod, as opposed to most multiple and
quench gaps. (2) Higher power can be accommodated simply by
increasing the air feed pressure (or CFM). (3) A single pair of
strong magnets can be mounted on either side of the brass gap to
assist quenching at even higher powers by dispersing ions away from
the arc and into the high speed airstream. (4) The electrodes can
be quickly removed for examination and/or cleaning without
disassembly of the gap. My electrodes require a light burnishing
with #1200 sandpaper after every hour of operation. The procedure
takes less than 5 minutes.

Using a diaphragm compressor, it is not necessary to regulate the
output. Just hook up and run the compressor flat out. The lower
output (CFM) of the diaphragm compressor reduces quenching, but can
be overcome by using an old portable propane tank in series as a
holding tank. A full tank of air will supply air flow for quenching
at higher power.    

This gap hisses like a large snake when the air feed is turned on.
When you hit your power switch and feed juice to the coil this gap
will take off. The noise is similar to a chain saw run full
throttle without a muffler. Indoors, hearing protection is a must.
Outdoors, your neighbors are sure to complain!