Dear Michael,
I am sure many people will be extremely interested in this. How hard is nitrogen to buy/plumb in? I assume you use manual control of the gas bursts?
Cheers,
R.
I have been processing sheet film in 3.5 gallon tanks for 30 years with gaseous burst agitation, although I only use gaseous (Nitrogen) burst agitation for color materials, not b/w.
In the United States, one gets bottles of Nitrogen gas from Welding Gas supply vendors. They usually deliver. Generally speaking one rents the cylinder (gas bottle) and pay for the gas. When you use it up, they exchange the cylinder for a full one. You can also purchase the cylinder, but when it comes time for more gas, they still exchange the cylinder, it is just that you have no rental charges. Nitrogen is an "inert" gas (non-flammable), therefore does not have the same restrictions on it that some other gases do.
I built a control panel consisting of a greylab timer for overall process timing, plugged into this is another industrial timer that makes one revolution per minute, around the circumference of this timing wheel are tabs you can move in or out. In the positions where the tabs are out, they press on a microswitch. Thus you can set any interval of "on" for the microswitch during a 60 second cycle. The microswitch sends power to a 110v solenoid air valve that opens and shuts the gas from the processing line. Of course you absolutely must have a gas regulator on the cylinder, from which you regulate the pressure down to just a very few ounces. Well, when you turn on the greylab timer, it starts timing the processing step, and in addition sends power to the 60 sec programmable timer which starts the burst cycles of nitrogen to the tank. I have wired an override switch across the contacts of the microswitch in the timer, so as to give me the option of continuous burst for initial agitation.
The plenums that bubble gas up thru the chemistry are just made from some salvage stainless steel tubing bent into a squiggly multiple "S" shape in the bottom of each tank, with a long straight bend up and out of the tank at a corner. From this you can attach a hose to the gas supply. The stainless tubing has little holes drilled on the bottom side of the squiggly "S" shape on the bottom of the tank.
This is the simplest description I can give of my set up. Mine is actually a little bit more complicated because I can also send compressed air thru the same system for the aeriation of the bleach and fix steps of E-6 and C-41, so there is some additional duplication of parts not needed if you are just considering using gaseous burst for b/w processing.