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Thread: Preparing for a Grow Rack -- Reverse Osmosis Units

  1. #9
    Tony Paroubek's Avatar
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    It will depend somewhat on the faucet. First thing is to unscrew the aerator from the faucet and bring that with you to the hardware store to match the one side. Kitchen faucets usually have threads on the outside so you will need a female fitting. Bathroom faucets usually have the threads on the inside so you will need a male fitting. They make fittings that will go from either faucet to a female hose fitting. They are usuually in the brass fittings/adapters in the plumbing section.

    All the RO units I have seen have a female hose fitting on the water input tube. You could use this or remove it and get another fitting that will slip into the tubing on the unit. There are alot of options for the unit side. It depends what kind of adapter you find for the faucet side.

    Once you remove the aerator there will be plenty of water flow through the faucet so as not to impede operation of the unit from insufficient water flow. The limiting factors at that point become line water pressure and less so temperature since you can feed a little from the warm water side if you don't mind paying to heat up your water before dumping 3/4 of it down the drain.
    Is that a Nepenthes in your pocket or you just happy to see me?

  2. #10

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    Another question. If i got a unit that could run off of a water hose and use it outside, would the waste water be much worse than tap? If i collected the waste water from it into a bucket or something would i be able to water the same things i use tap water on?

    Thanks. This is a great thread... just in time too.

  3. #11
    rattler's Avatar
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    depends on what your water is like........the waste water from ours would kill all but the most alkaline tolerant plants........
    cervid serial killer
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  4. #12

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    Thanks. I appreciate the help you all have given so far. I have a few more questions.

    1) After a lot of research, I'm thinking this is just easier and probably cheaper in general to put under your sink with a saddle valve. I have read many recommendations around the forum for pumps to raise the pressure of the RO system. Most of the directions I could find with google didn't really get into pumps. So why the recommendation to get a complete system with a pump up front? Is this more of a just in case type of thing or is it something that would improve the operation of the unit regardless of initial line pressure?

    2) Im unclear how the units stop running. Is this purely based on pressure inside the storage tank and water pressure or is this an electrical switch? Does the storage tank require power for pressure or is this achieved from the line pressure?

    3) Regarding the recommendation for a higher GPD than you expect to use. If there is a 2 or 3 gallon storage tank, is this as much of a concern? I understand the price difference between a 50 gpd and a 100 gpd is relatively small... but if I find a good deal on a lesser model is it likely I would even notice a difference at the tap? I dont imagine i would exceed 20 gallons per week but i never really thought about what my water use is for cooking/drinking.

    4) And lastly, my sink has 2 drains... left and right. The left one has a garbage disposal connected and the right side has the dishwasher. Where would be best to connect the drain line? Bear in mind im about to replace the disposal and the trap kit with new parts... so reconfiguring a bit isn't a problem.

  5. #13
    Av8tor1's Avatar
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    Abc,

    There are two different pumps really, a permeate and a booster...

    RO systems are highly dependent on line pressure, so if you have low line pressure then you will have to use a booster pump or the system will not work properly (somewhat common) or not at all if the line pressure is excessively low (rare).

    Ideal = 60psig, anything below 45psig will start causing problems with 50 being the recommended minimum and 80 the recommended max (typical)

    Lower pressure = lower efficiency, lower rejection ratio, increased recovery time, increased brine ratio, decreased prefilter and membrane life

    Normally if someone is having repeated issues with their RO system, this is the root cause.

    However, if the pressure is fine, then its not needed unless you just want to tweek the system for max performance

    Permeate pumps are the other hand are primarily used to overcome the decrease in pressure differentail across the membrane and the jump in brine rate as the holding tank fills. This wastes water, lowers membrane efficiency, increases recovery time and decreases prefilter life.



    (notice that the membrane outlet pressure remains a constant 5psig regardless of tank pressure)

    Permeate pumps while not required, are a very nice upgrade. They can really increases filter life and rejection ratio on captive tank systems. Usually anyone who has installed one will tell you they love it.... plus they just sound kewl LOL

    (They can also help with low line pressure issues, but this is not their designed purpose)

    So when you research pumps be sure you are comparing apples to apples mate

    #2 = if it is a captive air tank (accumulator) type system, the system is shut off buy a hydraulically operated auto shut off valve. It will shut off the inlet flow when the output pressure is approx 60% of inlet pressure. If you upgrade with a permeate pump, you can swap this out for a 90% ASO valve (auto shut off) or no ASO valve at all since the tank pressure is now isolated from the membrane outlet. (maximum membrane pressure differential is maintained regardless of tank pressure (the permeate pump isolates the membrane outlet and "pumps" the permeate into the tank.)

    #3 The gpd rating is of the membrane with "ideal" pressure diff and water temp. This is not a "real world" value to begin with, plus the larger system will give you faster recovery times. Normally its also easier and cheaper to find the 100gpd membranes when you need a replacement.

    Membrane Output Calculation
    Membranes produce the rated gallons per day (GPD) at 60 psi (4.1 bars) operating
    pressure, 77°F (25°C) operating temperature and 500 ppm total dissolved
    solids.
    Membrane output gallons per day (GPD) depends on operating pressure, water
    temperature and the ppm TDS in the feed water.
    Expected GPD = Rated GPD × PCF × TCF
    PCF is the pressure correction factor
    TCF is the temperature correction factor
    Calculation of Pressure Correction Factor (PCF): The output (GPD) from
    the membrane is directly proportional to the applied pressure.
    Note: The membrane is rated to produce the rated GPD at 60 psi. For any pressure
    other than 60 psi the output GPD is multipled by the PCF.
    PCF = Line Pressure (in psi) ÷ 60
    Calculation of Temperature Correction Factor (TCF): The output (GPD)
    also decreases with decrease in temperature. This is because water viscosity
    increases with decrease in water temperature.
    Temperature Correction Factor Table (TCF)
    °F /°C TCF °F \°C TCF °F \°C TCF
    41.0 /5 0.521 59.0 /15 0.730 77.0 /25 1.000
    42.8 /6 0.540 60.8 /16 0.754 78.8 /26 1.031
    44.6 /7 0.560 62.6 /17 0.779 80.6 /27 1.063
    46.4 /8 0.578 64.4 /18 0.804 82.4 /28 1.094
    48.2 /9 0.598 66.2 /19 0.830 84.2 /29 1.127
    50.0 /10 0.620 68.0 /20 0.857 86.0 /30 1.161
    51.8 /11 0.640 69.8 /21 0.884 87.8 /31 1.196
    53.6 /12 0.661 71.6 /22 0.912 89.6 /32 1.232
    55.4 /13 0.684 73.4 /23 0.941 91.4 /33 1.267
    57.2/14 0.707 75.2 /24 0.970 93.2 /34 1.304
    SpectraPure ®
    SpectraPure®Inc. Fax 480.894.6109 Fax us toll-free 1.877.527.7873
    E-mail: spectra@spectrapure.com Visit us on the web www.spectrapure.com 13
    Production Rate
    Membrane Output Calculation Example
    What is the expected GPD from a 75 GPD System at 40 psi pressure and 60°F
    water temperature?
    PCF = 40 ÷ 60 = 0.666
    TCF = 0.754 (from Table 1)
    Expected GPD = 75 × 0.666 × 0.754 = 37.7 GPD ± 15%



    #4 as long as the drain will not experience any type of "back" pressure from the plumbing and maintains some type of suction break.,

    Av

  6. #14
    mark.ca's Avatar
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    I got my system on ebay too. Payd like 80$ for a "0 ppm" unit. I don't get a 0 ppm ....i get around 10 ppm wich is more than fine by my standards...no tank on mine but i do suggest to get one. It's a 5 stage filter unit.
    Best regards,
    Marius

    My Website: http://droseragemmae.com/

  7. #15

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    Thanks for you replies. I think i got what i need to move forward with my RO system. Now to wait for payday.....

  8. #16
    mcantrell's Avatar
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    Got my TDS tester a few days ago. 350+ TDS in my tap water. Yeow. RO Filter is the way to go, I guess, but given the hard water stains everywhere, that was kinda obvious.


    So for home use, it doesn't matter too much as long as I get a carbon prefilter? And ... maybe a pump? How do I test my water pressure?

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