Perpendicular Air Blast Gap
This is the new perpendicular flow single static air blast gap I built for the 4" coil refurbishment project. It is based on 1" copper pipe and pipe caps housed in a 2" sch 40 PVC cross. The capped 1" pipe electrodes are slipped inside 2" x 3/4" bushings, which I modified with a router for a snug fit. The little squarish things at the ends of the Copper pipe are heavy-duty copper ground lugs soldered inside the pipes. The 2" cross is mounted to a powerful 120V centrifugal blower using a 2" x 1.5" bushing and a short stub of 1.5" PVC pipe, which by a stroke of luck fits snugly over the output port of the blower.
Performance is fine at 1080VA from two 9kv/60ma NSTs in parallel. It gets warm on longish runs, but not hot enough to damage the PVC bushings. This gap was not a deliberately planned design--I sort of ad-libbed it so as to make use of the big blower, which just happened to be in my junk collection. I found the blower while dumpster diving. I think it came from a shop vac, but I'm not sure. The gap is very easy to adjust. It requires no maintenance, and works fine without cleaning. It is rather loud though. BTW, the little vent holes drilled in the pipe caps are to prevent hot air from accumulating inside the hollow electrodes.