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#11
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I have a copper cylinder and a Pro-Co thermostatic mixer cost me £7 at a camera sale. The immersion heater keeps the tank hot (set at min. 55degC) easily as it does not take much hot water to maintain a temperature of 20 to 25C. It does need a small header tank which all fits into my garden shed. I would say you could get reasonable control with a shower mixer or even two gate valves in the cold and hot water supply before joining them to a tap. The gate valves would give pretty fine flow adjustment.
Tony |
#12
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The widest range of continuous-flow electric heaters is from the German company Stiebel-Eltron. They are intended for use with mains water pressure and won't work at all with typical loft-mounted storage tanks because the safety device will actuate at low pressure. The output is suitable for use with a thermostatic water mixing valve.
Storage hot tanks intended for domestic use are bulky and expensive and also require a thermostatic mixing valve because the heated water forms layers, hot at the top, cold at the bottom. The alternative is to install an inexpensive 3kW continuous-flow water heater intended for hand washing, which can be plugged into a UK standard 13A socket. It is also intended for mains pressure. This type has the flow control on the inlet - the vessel enclosing the heating element cannot withstand the pressure of a closed-off outlet. The temperature depends on the incoming temperature and is adjusted by limiting the flow. The performance is given by the equation (watts x seconds) / 4.2 = calories = temperature rise (in deg C) x volume (in ml). So if the incoming water temperature is 8 deg C and the desired temperature is 30 deg C, a rise of 22 deg C, the system will yield 1938ml, around 2 litres, per minute. If you set a temperature of 20 deg C (12 deg C rise) you will get 4.3 litres per minute. You will of course need a thermometer. Last edited by JOReynolds; 24th February 2014 at 07:03 PM. |
#13
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I pondered a lot in this question when I built my darkroom. The cheapest way is to do as Tony has done with a thermostatic mixer and a hot and cold supply. In the end though I went for accuracy and a wide temperature range from a pro co instant heater unit I picked up off ebay. It soon died. So I coughed up for an American eemax heater and doubled the cost of my darkroom .... but I have water at 20 deg or 40 deg whenever I want.
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#14
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#15
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Thanks for all your replies. It is obviously a lot more complicated than I first thought. What does everyone else do when washing FB paper? Do you run it straight from the cold tap or use water a little warmer? Do the Heatrae type heaters plug into the normal ring main?
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#16
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Jeff - Heatrae manufactures a range of heaters, some of which can be plugged into a 13A ring main. PM a description of what you need and I will do the calculation.
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#17
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Water coming in is at 2bar... not sure what the minimum is for the unit. I also run it through a filter after the water is heated rather than before. |
#18
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Just wonder how importent water temperature is for washing prints. Ilford times for washing are for temperatures above 5degC with no reduced times for warmer water. I doubt if mains water temperature falls below 5degC except on very rare occasions.
Tony |
#19
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Having read through all the replies I'm certainly a lot wiser than before. I did nearly buy one off ebay but after reading forum replies I decided to pause. The one off ebay sounded just right, about £50 fitted under the sink and temperature depended on flow so my thoughts were to fine tune the flow to get the right temp. In the end they said I needed a separate 16A supply so abandoned that. As Tony says if print washing above 5 is fine then perhaps just having one of the wall mounted storage ones for washing and chemical mixing use you would suffice. This has all been triggered because I picked up a 4' x 2' Pro Co sink off ebay in wonderful condition for a song. I have been using a corroded domestic sink but when you are washing trays the stuff gets everywhere so now I will be able wash the trays with plenty of room to spare.
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