Great article David. I see that I was a bit naive in it's design and can think of several ways to improve it. I think I'll make a PVC pipe bar across the bottom to inject streams into each print cell. this could be removed and swapped to the other side periodically during wash to achieve some sort of reverse flow. Using corrugated plastic cardboard might not of been the best idea. The inside cells of the board can trap retaining contaminants and would be very hard to clean along with the surface of the cells being smooth. It would be better to replace them with some textured surface plastic or acrylic sheets. Back to the drawing board..
The Versalab uses the same general divider approach as your design. Water input is via a tube across the top at one end with holes lined up with each partition. Drainage is at the other end using a siphon with a break (a small hole in the top of the tube at the water surface - when the hole submerges the siphon runs, as it drains the siphon stops). There's a lot of argument about fixer diffusion in wash tanks. If you rinse the print before putting it in the washer, and wash in batches it shouldn't be a problem. You can always run a wash test.
Ok, made the first improvement today. I bought a few dollars worth of PVC pipe and made a T spray jet nosle to insert down one side of the tank so that each print chamber will get a directed stream of water. You can switch it to the other side half way through the wash for reverse flow. This mod only cols $15 with the tub hose and faucet coupling cone included. See pics
Have you tried putting a few drops of dye onto a print and using it to check the flow patterns?
I read that Ctein article with great interest because here in AU, water is at a premium. I use the 4-changes-of-water method (with HCA obviously; a friend of mine has FB prints from 30 years ago washed with this method and they're fine) and have had good results so far, but the manual dumping and occasional agitation is annoying me. Not to mention my "washer" is the sink.
Has anyone considered making a powered washer with a small aquarium pump to recirculate the water and either change the water a few times or trickle-fill it at an extremely low rate? I reckon I could make a 3-sheet 16x20 washer that held maybe 15L of water, for a total wash of well under 100L. Given that fixer doesn't actually sink and that there's no way to extract the higher-concentration liquid, occasional dump+fill cycles will give better diffusion (lower average thiosulfate content in the wash-water) than trickle-flow at these rates. And of course one can use a geometric sequence of wash-times to account for reducing levels of thiosulfate in the print.
I have not checked the flow pattern yet but would be interesting to do so. For water conservation, you might consider the method that they mentioned in the article where you use a higher concentration fixer for a shorter time. It was interesting how little the print absorbed when fixed for 1 minute.
My last mod. I added a cheap pump on the opposite side of the inlet jets that pumps water from the bottom into a spray jet bar that runs across the top of the chambers and points back towards the input side, setting up a circular water flow in each print chamber. Water spills out the top on the inlet side.
Thanks for the tips on building a print washer. I am looking for a larger washer as I am doing 16x20 prints and I am just using a large tray on a slant into the floor drain. It cleans OK but it gets quite messy after a few prints. And I do know of a pet store in my neighborhood that just closed and several large aquariums collecting garbage in the back. They were designed for display so they are long but not very wide + or - 12". Ideal for this. Dennis