Continuous Mix Blending Stick
1. To make our Mixing Stick, we started with a 2" piece of ABS/PVC pipe, some 1 1/2" PVC caps that fit tightly inside the ABS, and a 1 1/4" piece of 1/8" thick aluminum flat bar. I think all the parts combined, including the hose clamps, mounting hardware, elbows, etc. were less than $40 at Home Depot. This was way, way cheaper than buying a ready-made stick.
Click on any image for a larger version.
These were drilled by hand, but a drill press would do a neater job if you happen to have one handy. I think these are 3/8" holes, and I kept them to one side of the cap so the air flow would have to go around both baffles.
Be very careful that you hold the cap securely with the hand clamp. Also be very careful in the placement of the clamp so your blade doesn't strike the hand screws. The picture doesn't show it, but I used a small square of plywood to keep everything indexed, square and lined up correctly.
It worked slick as a whistle! You could do the same thing with a table saw, or even a hand saw if you are so inclined. The 1/8" thick kerf created by the saw blade matches the thickness of the aluminum flatbar. Almost like we planned it that way!
We then cut semi-circular parts from the aluminum flat bar using a 1 1/2" hole saw. If you line up the hole saw so it just catches the edge of one side of the flat bar, you'll get a nice fit with just enough space on the other side for good air flow. These plates are then fit into the kerf slots cut into the caps. We wrapped electrical tape around the caps to keep everything snug and used some scrap PVC stock for spacers (that long sections with large holes in the side are just scrap material used to separate the caps, use whatever you happen to have in the garage). Then the whole assembly slides into the 2" tube, and a hole is drilled and taped for the Oxygen inlet.
The tube was topped with an air filter designed for a lawn mower and then a 3" PVC cap to keep debris and insects out of the mixing stick. The final product works like a charm!
This works so well in fact, that when a local dive shop's $2500 Nitrox Stick was stolen from the outside of the building, I made up another one of these for them (total cost for all the parts was less than $40), and they are pleased as punch. They are actually using less oxygen than they used to, and getting much more consistent mixes. I did change the design slightly for the Dive Shop, as their compressor has about 4 times the throughput of mine. I drilled extra and larger holes in all the Caps, and drilled a couple of holes in the bottom baffles of the last two stages to allow for more flow.
They couldn't be happier, and it always feels good to help our your friends!
Buy the way, if you are going to build one of these yourself, you really should have Vance Harlow's book, "The Oxygen Hacker's Companion".