Pumps and valves for photo chemistry - which material?

Discussion in 'Darkroom Equipment' started by movin, Apr 20, 2012.

  1. movin

    movin Member

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    I'm thinking about building some kind of contraption that will take care of filling/ dumping the chemicals from the development tank.
    I think I can manage the mechanical/electrical side of things. The major Problem is my lack of knowledge about suitable materials that will both withstand and not ruin developer and fixer.
    Are plastics to be preferred to metals, which materials to avoid etc.
    I would appreciate it if somebody could point me in the right direction or share his experiences.

    Movin
     
  2. Bob-D659

    Bob-D659 Member

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    Avoid any metals except type 316 stainless. Up to 40C, most any plastics are ok. Nylon, PVC, ABS, styrenes for fabrication. If you are gluing parts, avoid polyethylene and nylon, really tough to glue.
     
  3. George Nova Scotia

    George Nova Scotia Subscriber

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  4. johnielvis

    johnielvis Member

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    pumps and hoses could work--probably the best controlled are the peristaltic types that use the hose as the pump--all plastic and no liquid touches the pump.

    the problem is how big of a tank? you want to empty/fill fast--for empty--that's easy--no pump needed--gravity can do the work better than any old pump. but filling like a big 8x10 tank--that takes my kitchen a while to do--filling/emptying quickly is a problem with speed that I can't see any way around--unless it's a BIG pump and a small tank.

    how about some kind of gravity drain and gravity fill system--you pour to a supply tank higher above the process tank--fill it slowly as you want---then that has a big pipe on it and whoosh when you open a flap valve--just like an old toilet design with the tank up high--that's about the most low tech and best speed solution I think there is---no electricity or nothing just set up the solutions on top and WHOOSH in they go while the old solutions go out...like use rinse water to flush out the developer..then let gravity drain the rinse water....you just need to have something higher up--and the drain has to be lower than the drain in the room too--those are the only 2 constraints..but I think that these low tech solutions are the best and can generally outperform any old pump--put gravity to work for you.
     
  5. johnielvis

    johnielvis Member

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    pumps and hoses could work--probably the best controlled are the peristaltic types that use the hose as the pump--all plastic and no liquid touches the pump.

    the problem is how big of a tank? you want to empty/fill fast--for empty--that's easy--no pump needed--gravity can do the work better than any old pump. but filling like a big 8x10 tank--that takes my kitchen a while to do--filling/emptying quickly is a problem with speed that I can't see any way around--unless it's a BIG pump and a small tank.

    how about some kind of gravity drain and gravity fill system--you pour to a supply tank higher above the process tank--fill it slowly as you want---then that has a big pipe on it and whoosh when you open a flap valve--just like an old toilet design with the tank up high--that's about the most low tech and best speed solution I think there is---no electricity or nothing just set up the solutions on top and WHOOSH in they go while the old solutions go out...like use rinse water to flush out the developer..then let gravity drain the rinse water....you just need to have something higher up--and the drain has to be lower than the drain in the room too--those are the only 2 constraints..but I think that these low tech solutions are the best and can generally outperform any old pump--put gravity to work for you.
     
  6. David Brown

    David Brown Subscriber

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    Why?
     
  7. Bob-D659

    Bob-D659 Member

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  8. movin

    movin Member

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    Thanks for all the suggestions.

    With a little bit of further research I found this extensive chemical resistance chart:
    http://www.buerkert.com/media/COM_Chemical_Resistance_Chart.pdf

    It actually has a category "resistance to commercial products" (p. 22) with photochemistry as one (albeit pretty general) item.
    Valves and pumps that only use materials with complete resistance to constant exposure are pretty expensive.
    Also they seem to be kind of overengineered for my application because they would not be in constant use (like in roller development machines)but only for a very short time.

    I think a system designed only around solenoid valves will fit my needs (both speed and cost). I am currently experimenting with this series of valves:
    http://www.rpesrl.it/product.php?lang=2&cat=10&p=3#3
    Results are promising and the prices are pretty cheap (24€ per valve).

    Movin
     
  9. Mike Wilde

    Mike Wilde Member

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    Look up Wing Lynch. They made a single shot automated film processor. You could process many 35mm or 120 films reels (Paterson type), as well as 8-4x5 at once or even 2 8x10, I think.

    Usually for E-6, but if you are up to making one from scratch you are up to modifying the resistor matrix board to modify the thing to run a B&W process for an 4 series machine.
    They made OEM B&W cards, but they are a fair bit rarer.

    I understand the Wing Lynch 5 series machines were cpu controlled, but I have not played with one of these to see how modifyable the programming is.

    Every small town lab that ever processed e-6 likely has one of these on the verge of being thrown out, now that e-6 film processing volumes have cratered.

    That is how I came by the one I had. It was neat to play with but I did not have the volume to make it worth my while to keep it.
     
  10. jodys

    jodys Member

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    There is a chapter on materials in "Handbook of Photographic Science and Engineering" 2nd Edition. IIRC, it covers in detail which metals, plastics, etc. are safe for use in photo-processing equipment. FYI, the book is well worth your time and money. It serves wonderfully as a reference to all things photographic (circa the mid-90s), with extensive references if you need more information.
     
  11. DREW WILEY

    DREW WILEY Member

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    Any true industrial plastic and pipe distributor should have chemical compatability info in their catalog. But I don't get it either. It is quite difficult to get pumps to fill and drain quickly for even processing. A lot has to do with the design of the drum or tank itself. High-end commercial lab processors are so so common and affordable on the used market right now, or even downright free, that it seems one could simply use one of these outright, or cannibalize one for parts.
     
  12. Lowly

    Lowly Member

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    But aren't all these commercial machines too large physically, and/or require commercial volumes for processing? I'm very interested in these threads where people design and build things for hobby uses/volumes.
     
  13. graywolf

    graywolf Member

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    Carboys of chemicals on an overhead shelf is probably the simpelist solution. solenoid valves could do automatic fills, or replenishment. The CNC hobby has brought a lot of computer controlled robotic stuff into the low budget market. However, if it is not used a lot, at least daily, a replenishment system does not make a lot of sense. But contrary to some comments, if you are using a replenishment system, you may not need that quick a fill, as you are just adding small amounts frequently. A solenoid operated dump rinse tank also does not need to refill all that fast, so what if it takes 5 or 10 minutes to fill as long as the film or paper does not have time to dry out, it will be OK; and smaller, like 1/2 gallon tanks should only take a couple of minutes to refill.

    This sort of thing is almost trivial nowadays.