Film processing: Agitation by pumping?

Discussion in 'Darkroom Equipment' started by knutb, Oct 11, 2005.

  1. knutb

    knutb Member

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    Hi.

    I have been thinking about building a home made automated film (b&w) processor - load the film, start the processor and forget the whole thing for a while :smile: Manual film processing isn't that much fun, consistency could probably be improved, and not least: it seems like a fun project. Some way of agitating the film will obviously be required, but the big question is how. Among others, a rotary processor is a possibility and mechanical inversion of a daylight tank should be possible... But what about using a circulating pump? Drain fluid from the bottom of the tank, feed it through the pump and return it at the top of the tank. Or place an impeller (more or less a propeller) at the bottom of the tank. A somewhat modified standard tank such as a Paterson could be used. Agitation (ie. pumping) frequency and duration can easily be controlled, and the system would contain no moving parts (well, the pump obviously has moving parts, but consider it a readily made black box for this purpose). Add a handful of valves for filling and draining the various liquids, and the device should be complete.

    Any comments on the principle of using a circulating pump for agitation?

    Knut
     
  2. FrankB

    FrankB Member

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  3. gbroadbridge

    gbroadbridge Member

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    You either want consistency (provided by a rotary processor), or consistency (provided by irregular inversion).

    A pump provides nothing but irregularity unless the film is also in motion.

    Graham.
     
  4. knutb

    knutb Member

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    Thanks for the link FrankB. I've seen ads for this processor, but could not remember who makes it. Interesting with a more detailed description of the design. Such an approach may very well be the safest, as it resembles very closely the usual manual agitation. It should also be possible to make a similar processor with automatic filling and draining. Among others, a modified tank cap would be required. Definately something to consider.

    But the pumping concept has a number of advantages, as the thing should be homebuilt with relatively inexpensive (as always) off the shelf parts.

    Knut
     
  5. Bosaiya

    Bosaiya Member

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    One thing I've thought about is modifying automated egg-turners. These are devices that sit inside an incubator and rock the eggs back and forth. Most have some adjustment of timing possible, and most will rock to one side a bit, wait a little, rock to the other side, wait a little, and repeat. They're very inexpensive.

    The problem as I see it is that the whole tray doesn't rock, just individual rows, but perhaps that would be part of the modification process.
     
  6. Michel Hardy-Vallée

    Michel Hardy-Vallée Membership Council

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    In light of the problem of designing an automated film processor, are there any processors on the market that can do agitation by inversion? I don't know, something like a paint mixer, but with a slightly irregular and intermittent pattern of agitation.
     
  7. Baxter Bradford

    Baxter Bradford Member

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    I have just constructed a tank for supplying water at 38 deg C for E6 to my Jobo. To circulate the water around the heating element for a uniform temp, I have used a 320l-hr mains operated pump for an aquarium. This is pretty small and quiet and ought to do the job.

    Not sure how much automation you require, but......

    To pump the water into the Jobo on demand, I am using a 12V submersible Whale pump from a camping shop which has proved effective. This (or even these if you get very ambitious!) might be employed to pump chemicals into the tank, but would need a timer to get correct amount of solution.

    Like Graham, my instinct is to have concerns about how uniform the agitation would be...... but I wish you luck and please keep us posted.
     
  8. knutb

    knutb Member

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    Egg-turners - cool idea..!.. Didn't think of that one - maybe because i didn't know that such animals actually exist :wink:

    mhv: Check out the link provided by FrankB.

    gbroadbridge: The general idea is to provide motion of the film relative to the developer, isn't it? What's the principal difference between moving the film (such as using film hangers in deep tanks) and moving the developer liquid by circulating it? In practice there are a number of challenges of course; such as providing a reasonably even flow distribution over the entire film area. Particularly for a spiral reel a la Paterson, this can very well be a problem, or maybe a show-stopper. I guess flow rate and pump pressure would be quite important parameters. A quick google search for (film agitation, pumping) gives several hits, but as far as I can see, these are about rather big automated processors.

    Knut
     
  9. Donald Miller

    Donald Miller Member

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    The problem that exists in pumping developer over the surface of film is that the laminar flow must be absolutely even or uneven development will result. Even a design with a manifold incorporating precisely drilled orifices will result in some uneveness because there will be a pressure differential and differing flow characteristics from the inlet to the terminus of the manifold.

    Stop and fixer would not be so critical.

    If I were going to design something of this type, I would probably look at a design incorporating agitation rather then pumped chemical flow. If I were to get so involved as to incorporate replenishment or dump and fill, I would look to peristaltic type pumps for their precision in volumetric delivery.
     
  10. Donald Miller

    Donald Miller Member

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    Jobo has a reputation for very even film development. Why reinvent the wheel? If someone wants to build something themselves, copy from their operating characteristics. That can be done without infringing on their patent rights.
     
  11. Bosaiya

    Bosaiya Member

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    Chickens? Yeah, they're something I've been working on for a while now...

    But seriously, here's a link to one. It's the first link returned by the search, I know nothing of the manufacturers product specifically:

    Automtic Egg Turner

    For what it's worth, do NOT use these for your incubating eggs, the mortality rate will be astronomical. Can't say if the same would be true for your negatives.