DIY Gas Burst Agitation for 1 gallon vertical tanks

[Sam L]

I spent some time making gas burst agitation for my 1-gallon arkay style tanks and wanted to share what I learned.

This older thread was extremely helpful:
https://www.largeformatphotography.i...gen-Processing

In particular, this part, which is based on a Kodak technical bulletin that I was unable to find: "The bubbles come out of the plenum 1/4" from bottom in 1/64" holes (Kodak recommends 1/32" or smaller) spaced alternately 1/2" apart at 30 degrees pointing down, in one second bursts every ten seconds at 35 psi, bounce off of the bottom and flow upward forming a closely and evenly spaced group of small bubbles. The rising bubbles don't agitate the developer, they displace it 5/8" inch."

My tanks are home-made but roughly match the standard dimensions (if there is such a thing) for a 1-gallon stainless tank: 2.5"w x 10.75"d x 10.5"h. This leaves about 0.75" below the hangers to the bottom, which is enough space for a 0.25" thick plenum, 0.25" below it and 0.25" above it.

The guidance for holes is "30 degrees pointing down," which I took to mean 15 degrees off the down-facing center line.

For my first attempt, I used a thin-wall stainless tube. While still straight, I used my mill to drill 1/32" holes every inch along a line at 1" spacing. I then rotated the tube 30 degrees and drilled the intermediate holes. I then bent the tube into a spiral and welded 1/4" rod horizontally on the bottom to help it stay aligned and to space it 1/4" off the floor of the tank. Here's how it looked:


Here is a close-up of the 1/32" holes pointing down, alternating 15 degrees off the center line:


I used a 1/4" compression to 1/4" female NPT adapter and a 1/4" NPT to 5/16" quick connect adapter to connect the plenum to 5/16" polyurethane tubing. The quick connect stuff is very convenient in use since I need to be able to put the tanks away and cheap on Amazon. Here are some of the connectors:


To test it, I adjusted the gas to get an approximately 5/8" fluid rise. The issue with this plenum was that the gas burst was uneven. Here you can see the bubbles forming on the first third of the tubing length:


The pressure eventually propagates to the end but the resulting fluid movement is more of a wave from front to back, left to right. Negatives developed with this plenum were uneven with more density where the bubbles were more vigorous.