Hi All; Been burning my 6" & 7" batches hot, all day everyday. Both are located in large poorly insulated building's.
After 3 months the cobra head on my shop batch spalled enough, to just fall off! Leaving me with an open top 3.5" tall tube.
Needless to say performance suffered.
I removed the door and then the secondary tube. As I have a full working shop, it was little effort to cut off the remains and build and weld on a replacement. Problem fixed! But maybe not so easy for others without metal working tools and a ready source of metal.
I started looking at the stub on our studio batch. I could see that it was spalling badly and was going to fall apart soon as well.
This is an issue eventually with any batchbox. But in normal use, several years is expected. Replacement could be accomplished casually over the summer and not winter while it is snowing and well below freezing.
I decided to design and build a secondary air tube with a quickly replaceable stub... before my studio batch stub rotted off.
I succeeded by about 5 days. The studio stub did the same thing the shop stub did, there one minute and gone the next!. I was glad I had a complete replacement tube with a quick change stub already built. It was about an hours work to completely replace the secondary tube. I switched from the shorter cobra head to the taller Walker pipe. Performance appears identical (I have no Testo meter ). Now when this pipe spalls down to a shorter length, it will take seconds to drop in a 6" piece of schedule 40 2" pipe at a cost of a few dollars.
For those of you with metal fabrication ability's. schedule 40 2.5" @ 1.5" tall with a 6" schedule 40 2" stub slips right in.
For the cobra style 1.5" tubing slips into 1.75" tubing.