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!
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Quoting Jerry Biehler :
> 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...
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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:
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
Highly Recomended
Richard Quick's Cylinder Static Gap
This cylinder static gap was designed to quench 6-8 kv running up to 1 kva in more or less continuous duty. It will quench 6-8 kv up to 2.5 kva intermittent, depending of course on your run times, three minutes being quite tolerable. These gaps are very functional and can be easily moved from coil to coil. Complex gap systems can be built up using more than one unit. These systems can provide excellent power handling flexibility and efficiencies. It is possible to tap the gap at the center electrode creating two equal and parallel paths within a single unit. Two gap units wired in this parallel configuration may be hooked in series for quenching up to 1.2 kva continuous, or 3 kva intermittent.
These gaps can also be employed with great effectiveness when used with a rotary gap. Units wired for parallel operation may be run in series with a rotary gap. Excellent quench times can be achieved at very low cost on medium powered Tesla coils in this fashion.
The copper pipe electrodes offer a large surface area to assist in quenching. The electrodes are cooled by an air stream which also removes hot ions from the gap during operation. The air stream is provided by a 5-1/4" muffin fan mounted on top of the gap unit. The gap is remarkably quiet, and the arc is shielded by the PVC pipe eliminating the UV hazard.
Construction of a gap unit requires the following parts:
A five inch length of 6" PVC drain pipe
15" length of 1-1/2 inch hard copper water pipe
One end cap for the 6" PVC drain pipe
One 5-1/4 inch, high CFM, muffin fan
14 1/4" Brass machine screws with nuts and washers
4 #6 Brass machine screws with nuts
3 feet of good quality lamp cord
18" of thick wall vinyl tubing
Stiff epoxy
Cut the copper water pipe into seven two inch sections and polish the pieces. Drill two holes in a line 1" apart and 1/2" from the top and bottom of each section.
Drill two corresponding holes, larger than those drilled in the copper pipe, into the PVC drain pipe. The holes in the copper pipe should be snug for a 1/4" machine screw. The holes in the PVC pipe must be loose, allowing play to properly gap the electrodes. Do not drill all of the required holes into the PVC pipe at once, work with one electrode at a time.
Mount the first electrode. Two 1/4" brass machine screws are used with the screw heads inside of the copper pipe and the threaded ends extending outside. Install a washer and nut on the screws and tighten until snug but DO NOT OVER TIGHTEN. Measure out ~2-1/2 inches and drill two holes for the second electrode. After fitting you may find it necessary to file out the holes before you can get a parallel gap. Use a feeler gauge and adjust until you can set a gap of .028 inches with the nuts snug. It is important that the gap be equal and parallel up and down the entire 2" length of the copper electrodes.
When the gap can be set, remove the first two electrodes and smear a stiff epoxy on the back sides around the screws. Reinstall the electrodes and snug the washers and nuts down, adjusting as necessary for a parallel gap. It is important that the epoxy gushes out around the nut and washer. As the gap is run over time, heating and cooling will loosen the mounting nuts unless there is sufficient epoxy on the threads to permanently affix them. Make sure to wipe away the excess and thoroughly clean the screw threads above the nut. The screws serve as the terminal posts and if the threads are fouled with epoxy you will have to fight to get your connections on and off.
Proceed with drilling the next two holes and fit the next elec- trode. Gap as above. When you can achieve a perfect gap, remove the electrode and bed it with epoxy. Check your gaps carefully and frequently, once the epoxy sets you will never have to worry about them again!
After all seven electrodes are installed, place the gap unit under a heat lamp to speed the epoxy cure. Then assemble the blower unit.
Center the muffin fan on the PVC end cap and scribe a circle for the fan cutout. Cut the circle out and drill four holes for the muffin fan mounts. Mount the fan with the four #6 machine screws and nuts so the air flows from the bottom of the gap unit up.
Slide the lamp cord through the vinyl tubing and solder the ends of the wire to the muffin fan terminals. The vinyl tubing is important to provide some protection from the high voltage present on the exposed gap terminals, but do not rely on it. Route your 110 volt line away from all high voltage points with nylon wire ties and provide for line filtering when using the gap.
When the epoxy has set, mount the fan assembly on top, but do not glue it into place. The top is removable for easy cleaning between the electrodes with #600 or higher sandpaper wrapped on a shaved down tongue depressor. I build a wooden or plastic tripod base to set the gap unit on. The gap base should allow at least 3" of space below the gap unit for airflow, I allow 4 inches.
The gap as sketched shows the installation of an arc shield between the two end electrodes. This is important despite the fact that the gap here is quite large. With a piece of 3/8 inch plexiglass glued in this spot, gap units can be run together in series to quench higher voltage power supplies without the arc taking the shortcuts.
When run with neons at 12 kv rms, two gap units are used and all the electrodes are run in series. If higher voltage is used (up to 25 kv) gap units may be added in straight series connection providing your kva load does not exceed the individual gap unit rating for long run times. Allow 1000 volts per gap between electrodes (.028").
When more transformers are added to the coil, the capacitance is increased correspondingly, input voltage remains the same. Higher tank currents require that the primary arc be split into parallel paths to cool and quench. To meet this requirement additional gap units are added but all gaps are tapped at the center electrode and the two end electrodes are connected together with copper or aluminum strap. The second gap terminal is taken from this point. The gap is now wired for parallel operation, it will handle twice the current. A second unit is configured the same way and added in series with the first. The resultant gap system will handle twice the current at the same input voltage. For highest "Q" all connections should always be made using both available terminals from the tapped electrodes.
Quenching performance can be increased by mounting an air choke on the gap base. This will act to prevent air from passing up the center of the gap where it takes up little heat and fewer ions. I use a piece of 3" or smaller PVC pipe set on the gap base and passing up into the bottom of the gap just under the electrode ring. This forces the air to pass through the electrodes and between the gaps to remove heat and ions and improves the run time. Performance may also be improved by fitting finned, cylindrical heat sinks, available at the electronics surplus or many hamfests, into the center of the copper electrodes. A little heat sink paste here is helpful to assist in heat removal from the electrode and preventing corrosion from the aluminum/copper contact. Oxides formed by contact corrosion are poor heat conductors. For maximum effectiveness the heat sinks should be cleaned of any coating at the contact points. Finned heat sinks installed in this fashion will dramatically increase the surface area of the electrodes. This is especially true in gaps of this design using larger copper pipe and bigger gap rings.
When running these gap units as part of a system with a rotary, all gap adjustments are still made on the stationary electrodes of the rotary gap. Insert one .028" static gap (distance between each electrode in this unit) in series for every 2000 volts of line input to the coil, then set the rotary gap adjustment so that the coil system fires smoothly and reliably. Suppose your rotary system has a 12 kv line input: every electrode on the cylinder static gap unit is gapped at .028", and you need a total of 6 of these static gaps in series with the rotary for the system to function properly at 12000 volts. There is no limit to the number of parallel paths that can be theoretically used, but two is the practical limit with this design. Two cylinder static gaps hooked up for parallel operation, and run in series with the rotary will provide excellent quenching up to 2 kva continuous, 3.6 kva intermittent. Your rotary will require a much smaller gap, and your quench time will have dropped considerably. Your rotary will run cooler, your run times will be longer, and your secondary spark will be better.
Another benefit of gap systems with a rotary is that the wear caused by the hot arc is distributed among many gaps with a large surface area. The arc at the rotary is both cooler and shorter in duration, taking stress off of the stationary electrodes and reducing wear at these critical points.
Gaps of this design using 1" diameter copper pipe can be constructed as above to get 12 gaps into a cylinder ring of 13 electrodes. The 1" diameter pipe sections do not sink as much heat, but if gapped at .028 -.030 inches a single unit will quench up to 15 kv rms from neon sign transformers banked up to 1.5 kva intermittent. If the unit is constructed from 1" dia. pipe and the electrodes are gapped at .056 -.06 the arc can be split down two parallel paths (center electrode tapped) for a good quench time with a neon power supply of 12 kv rms in the 1.5 kva power range, this is of course intermittent operation but will use only one gap unit. Using the flaired end of 6" pvc drain pipe will give enough room to squeeze in all of the required electrodes and the arc shield, but the result is the fan must be custom mounted, and may have to be glued into place.
Ä Area: UUCPE-Mail ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
Msg#: 2938 Pvt Date: 11-22-95 18:41
From: Richard Quick Read: Yes Replied: No
To: Froula@cig.mot.com Mark:
Subj: Cylinder Gap Mods for 15
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
* Carbons Sent to: usa-tesla@usa.net
tesla@grendel.objinc.com
Quoting Don Froula :
Richard, a quick question on the archive site cylindrical gap design.
Shoot!
I'll be running a 15 KV supply at 90 ma. initially in my new coil, using one of the commercial caps that we recently ordered. I'd like to try out the cylinder gap design initially, but noticed that the number of electrodes and gap spacing is designed for a 6-8 KV system. I was wondering if any design modifications, particularly gap size, could be done (short of building two units) which would allow 15 KV operation at 1.4 KVA.
This design is easily modified for various voltages and power levels. The simplest modification for higher voltage applications is to make the electrodes smaller in diameter, which means you can fit more electrodes into the unit = greater number of gaps. In order to sink the heat and distribute the ionized gasses better when using electrodes of smaller diameter it helps to make the electrodes twice as long, which means building the gap out of a longer length of PVC pipe.
Another solution is to use larger diameter PVC pipe. This allows the placement of additional copper pipe electrodes within the gap without having to use smaller diameter material.
Also, I was planning on using the surplus end from my 1/8" wall, 6" diameter acrylic secondary form to build the gaps. I have a 9" length left over from my 27" secondary form. Aside from the lack of UV protection, do you see any problems with this.
None at all. If care is taken in the construction it could look quite attractive as well as being exceptionally functional.
Thanks once again for the help. The secondary will be wound after Thanksgiving dinner tomorrow (hopefully). The pile of parts in the workroom is growing steadily. My wife smelled the ozone in the basement from the transformer tests the other night, and gave me that "oh no, not again" look!
HA! We have planned nearly identical activities for this block of time. I think sometimes my wife wishes I would watch more football...!
Richard Quick
... If all else fails... Throw another megavolt across it! ___ Blue Wave/QWK v2.12
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