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RE: Vacuum Gaps
Hi Don,
>Scott, your vacuum gap design sounds interesting. Is it similar to the
>unit in the RQ video (copper pipes friction fit into a plywood
>manifold box)? Any construction details, in addition to your plexiglass
>support problem solution, would be very helpful.
The principle is exactly the same as Richard's. I just used different
materials. Richard's also has been made so a rotary gap can slip in between the
2 sets of series vacuum gaps, to minimize wire length, hence extraneous
inductance and wasted energy. I assume that is the reason for this, although
Richard didn't tell me why and I didn't ask.
I built my vacuum gap before I realized anyone else was doing it. I thought I
was the first. I found out later that I was far from the first. Here is how I
built it.
First, I got some approx. 1/8" thick acrylic. It was scrap from the local
plastic supplier. It happened to be clear smoke in color. I then proceded to
the local vacuum cleaner repair shop and dug through their old vacuum motors
that were still good. I opted for a vacuum out of a "Tristar" vacuum, high
power and relatively low noise. The shop vac motors scream in comparison and
don't have as much power.
I built what looks like an oversized square shoebox out if the arylic using the
acrylic solvent which cures in a matter of seconds. The edges of the acrylic
must be very straight and fairly smooth to use this type of solvent. The lid of
the box can lift off. I cut a hole in the lid that accepts the vacuum motor.
The motor itself extends out the lid with the vacuum portion inside the lid.
Inside the lid, I placed a gasket made of some window strip foam that I had.
Now to build the gaps.
First, I must mention that this is a smaller gap system using only 3/4" hard
copper. I intend to only use this with my low power 6000 VAC supply on a 4"
coil. I cut 8 pieces of the pipe, 2" long. I squared the ends with a belt
sander, made sure that I had the lengths within .005" of each other with dial
calipers. I shined them up with some 200 grit emery cloth. Then some copper 26
gauge sheet metal was cut into pieces 1/4" x 1". Before it was cut, holes were
drilled in each piece near one end to accept a #8 brass screw. The same end
with the hole was rounded on the outside so it has no sharp corners. On the end
without the hole, I bent 1/4" of the strips to a 90 degree angle. This small
area was then bent to a slight radius so it formed to the surface of the 3/4"
copper pipe. Using a propane torch to tin the mating surface of this piece and
a matching area near one end of the pipes, I placed the pieces together and
sweated them together with the torch. I again shined them up with the emery
cloth after removing the solder flux. That completed the electrodes.
My plans call for grouping the electrodes in groups of four, although there is
really no need. They could be all placed together. I grouped them this way due
to the size constraints of the acrylic I purchased and to keep the vacuum box a
small as possible ( it is 8"x8"x6" ). I cut out four pieces of acrylic for each
group of four electrodes. 2 pieces are square and 2 are rectangular. The
square pieces I carfully sanded down on one side until they were less than .010"
longer than the electrodes are long. The rectangular pieces are cut so that
when the 4 electrodes are lined up together, that there is plenty of room to
space them out. I cemented the four pieces of acrylic together to form a
rectangular box that has no top or bottom. Holes were drilled along one edge of
the rectangulat longer pieces, a little more than 3/8" in and spaced out a
little more than 3/4" from one another. The bottom edge of this open box (the
edge away from these holes) was sanded down until it was flat and smooth. This
was repeated to make another identical small box for the other 4 electrodes. I
laid the sanded open end of this small electrode box on the larger box, about
1/2" from the bottom of it so that the long side of the small box was parallel
with the large box bottom. I drew a line on the larger box using the inside of
the electrode box as a template. I then cut this out. I repeated this for the
other electrode box on the next adjacent side of the vacuum box. I then
cemented each of the small electrode boxes to the vacuum box over these newly
cut openings. This finished the plastic construction. I must note that I have
sanded all cut edges that were cemented and sanded and flame sealed all
uncemented edges of the acrylic to prevent cracking and grazing, and for
asthetics.
The electrodes were the slid into the 2 open electrode boxes that were on the
sides of the vacuum box. Threaded rod and lock nuts were used through the holes
and through the electrodes to squeeze the acrylic enough to hold the electrodes
in place. I then connect the 2 groups of electrodes by HV cable between the
electrodes that are closest together. I filled the ends of the gap boxes where
there is no arcing with some foam insulation to insure that I could get as much
air as possible between the gaps, with no leaks elsewhere. This finished the
original vacuum gap. All that has to be done is to wire in the vacuum motor and
turn it on. I found that I needed to use only 5 of the available 6 electrodes
gaps for my 800 Watt, 6000 VAC supply, gapped at .020". Using all 6 proved not
to be completely reliable with 600 VAC. I could alway bring the gaps closer and
use all 6 if I wanted to, but the 5 gaps -at- .020" works fine and provides VERY
GOOD quenching.
I did have to make one modification. I noticed that after less than 30 minutes
total run time, bad carbon build up occured at the ends of the plastic. It
probably would have occured almost instantly at a higher voltage. I had to
figure out a way to prevent this from occuring. I contacted Richard Quick to
see what he did to prevent this from happening. Here is a previous message I
sent out outlining the 2 methods to prevent this problem.
---------------
Method 1 is to drill holes through the acrylic at the point where they intersect
the electrode gaps. This keeps the ions from gathering on the plastic and
promotes additional air from down trough the gaps keeping the arcing from the
ends.
Method 2 is to use spacers that are narrower than the gaps to keep their ends
from touching the acrylic at the point of the gap. This also promotes
additional airflow at the ends keeping the arcing away. RQ felt that this
method is the best.
I opted to use the drilled hole method, due to it being a little quicker to do.
I will change to the other method on my next larger vacuum gap. On my small
gap, it seems to work fine. Quenching is back with a vengence.
--------------
Keep in mind that this is a gap I designed from scratch with relatively low
power in mind. With higher power, you will need to insulate the pipe's heat
from the acrylic. It would also require too large of a hole with method 1and
you would lose too much vacuum. Velocity and air volume should be increased at
the electrode's ends with higher power/larger 1-1/2" electrodes to promote the
sparking toward their centers. Method 2 is definitely the best for this. The
thickness and material choice for your spacers will have to be carefully
considered. Too thick and you get too much wasted vacuum. Too thin and the arc
goes back to the ends of the electrodes driving quench times up (bad). The
material selected should be capable of withstanding about 300-400 degrees
Farenheit, to be safe.
The heat I have seen from the gaps has been minimal, even with 3 minute runs.
But again, it has only seen 800 Watts.
I have experimented with static, static series, single vacuum, series vacuum and
air blast gaps. Of these, the series vacuum as I described above works the
best, BY FAR! (The air blast is a closest second, but requires too much extra
hardware) It is reliable and I don't need air compressors or tanks. Quench
times are great. I recommend series vacuum gaps highly.
That's it. I hope it was helpful.
Scott Myers