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DIY Gas Burst Agitation for 1 gallon vertical tanks
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:
Attachment 223489
Here is a close-up of the 1/32" holes pointing down, alternating 15 degrees off the center line:
Attachment 223490
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:
Attachment 223491
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:
Attachment 223492
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.
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Re: DIY Gas Burst Agitation for 1 gallon vertical tanks
From the first plenum, there were a few things I wanted to improve:
1. 1/32" holes were too big. Too much pressure was dropping in the first few inches of tubing because it wasn't restrictive enough. Increasing pressure would make the bubbles more even but the resulting fluid rise would be so great as to overflow the tank.
2. There was no way for the pressure to equalize between the three legs of the plenum
3. Bending the stainless tubing was hard and I couldn't get the legs to run directly under the hangers so that the bubbles would travel along each face of the negatives
For my second plenum, I chose copper tubing. Though it is more reactive than stainless, it is much softer and is easy to solder. I couldn't reliably drill holes smaller than 1/32" in stainless but in copper it is possible. I bought 1/64" carbide drill bits from ebay, which are inexpensive and readily available as surplus from PCB manufacture. Rather than bend a spiral out of the tube, I cut and mitered short sections and soldered them together using plumber's solder and a torch. The layout includes crossover tubes at each end to help balance the pressure across the three legs. The legs align under the hangers. Here's how it looked:
Attachment 223493
And here are the 1/64" holes:
Attachment 223494
The bubbles from this plenum were much more evenly distributed at lower pressures:
Attachment 223495
I have been able to achieve much more evenly developed negatives with this plenum.
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Re: DIY Gas Burst Agitation for 1 gallon vertical tanks
The next challenge was to control the gas bursts. In spirit, the mechanism is very simple: a solenoid on a timer. Amazon has 12VDC normally closed solenoids for about $10. These can be controlled in various ways, but I chose to use an Arduino driving a relay. Getting into how this works is beyond the scope of a forum post. I'm happy to share the code but if you know what to do with the code you probably don't need the code!
Here's the controller:
Attachment 223496
An easier option might be to find an on/off timer that can be adjusted down to seconds and connect that to the solenoid.
I made mine adjustable in the same ways the commercial ones were, but found that every change to timing I tested made the development less even. I suggest it is sufficient for the controller to only do 1s on 10s off.
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Re: DIY Gas Burst Agitation for 1 gallon vertical tanks
Finally, the gas source. Everything I read suggested an industrial gas bottle of nitrogen, which is inert and so won't oxidize the developer. I don't have a nitrogen bottle, but I do have argon for my welder (much more expensive but also more inert) so I did most of my testing with that. Connecting the quick release fitting to the flow meter was not easy. I ended up with a hack: a short length of flexible tubing and two hose clamps from home depot:
Attachment 223503
This worked ok but flow meters are not regulators and so they can't maintain constant pressure for bursty loads. This doesn't matter at 10s intervals but at shorter intervals I tested it did not work. A proper nitrogen regulator that can handle low pressures is better (and the quick connect would just screw in):
Attachment 223504
Industrial gasses are really a pain. The bottles are heavy and the stores that sell gas are generally hostile places for regular people. If you are going to go this way, you may want to buy an "owner bottle" (non-rental) locally and swap it for a full bottle at the store. However, it turns out none of this matters because if you have a compressor and use one-shot developer you can just use compressed air. Here's how to hook your compressor to the plenum:
Attachment 223505
Everything I read suggested using inert gas was important but I tested compressed air and development times were unchanged and the negatives look good. I toss the developer after one use anyway so it doesn't matter if it is oxidized.
Re: DIY Gas Burst Agitation for 1 gallon vertical tanks
Re: DIY Gas Burst Agitation for 1 gallon vertical tanks
Re: DIY Gas Burst Agitation for 1 gallon vertical tanks
I should have used all SS fittings, too much $$$
The very quiet compressor is in the furnace room then through the wall with water into a spare bedroom, now totally blacked out
No need for black paint
I have a Snap-On pencil air gun that takes 25 psi down to almost nothing for dust
There are 6 enlargers on the dry side
Adding Alt Process fake Sun
This DR was moved from a bigger Chicago space
Re: DIY Gas Burst Agitation for 1 gallon vertical tanks
That's an impressive set up!
Are you seeing corrosion on non-stainless fittings?
Re: DIY Gas Burst Agitation for 1 gallon vertical tanks
I bought my own gas bottle online and just swap them out at the welding gas store. They price it very reasonable for me the times I was in there. The other item that one needs to remember is inert gases will aggregate in your darkroom displacing oxygen which is a concern if your darkroom is small as in oxygen deprivation which can be a very serious personal safety issue. So vent extensively and concurrently introduce fresh air supply into your darkroom continuously. Safety first. Compressed air obviously takes this variable completely out of play.
Re: DIY Gas Burst Agitation for 1 gallon vertical tanks
I used huge amounts of N2 in 5K big bottles in rooms smaller than my DR for 30 years
I would often use the whole bottle in one minute
Yes we had massive fresh air in and bad air out with doors wide open
I worried more about dropping one and knocking the valve off, instant torpedo, we watched the safety movie
A scarier thing was HALON misfire, 20 seconds to get out
But nothing get your wits up like indoor gasoline leaks at 150 psi
