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post #21 of 26 Old 11-01-2010
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Originally Posted by RichH View Post
Midwest RO Reverse Osmosis and Water Filters and Membranes in Illinois is probably the cheapest. Probable best and most compact hi Pressure pump is the Giant Model 218 @ $350.00 (brass head not bronze).
I am researching building my own watermaker. If I do it, I will detail the process here and what I bought and how I did it.

One question: On the WM's you have helped put together, did you use a electric motor or engine driven?

Also, who would you reccomend for the membrane? I have a couple of sites I am looking at, but curious who has bought/has experience with them?

Thanks.

Brian

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post #22 of 26 Old 11-01-2010
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Open question:

I have a bit of a problem to work through.

I have a 3.5kw generator. That would be my preferred method of running the watermaker. However, I will be limited to 26 amps max. In reality, I should keep it under 23 or lower, with lower being mych preferred. I have the HP on my main engine to run a watermaker, but unfortunately, not much room. So the preference really would be a Generator run watermaker.

So, most of the watermakers call (ideally) for 3-4 gpm with 1000 psi. That will be difficult to obtain and stay under my parameters as I suspect that will take a 2.5 hp motor. As such, do you (G LUcas or Rich H or others) feel that I can run a 2.5 X 40 with 3-4 gpm and 800 psi? I hav been told, not sure it was reliable, that 800 psi was the test pressure for most membranes and should be fine.

Also, regarding motors, I have several to choose from. Rich suggested a Giant motor which only pulls 17.5ish amps. Another option might be this Baldor EL1405T:

http://www.baldor.com/products/specs.asp?1=1&page=1&catalog=EL1405T&exact=1&product=AC+Motors&family=Premium+Efficiency|vw%5FACMotors%5FPremiumE fficiency&winding=36WGY526&rating=40CMB%2DCONT

It is a premium efficiency motor and might be a better choice as it has a lower draw, but am curious what others think of it??

So there is a start. Thanks for everyone's opinions.

Brian

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post #23 of 26 Old 11-01-2010
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Another question on watermakers:


If I reduce the GPM, that will only reduce the output, right? If I want max output, I must maintain max GPM? But if my putput drops to say, 2.8 gpm versus 3-4, but I maintain my 800+ psi, I will only make slightly less than rated water, correct?

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post #24 of 26 Old 11-01-2010
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The 800 psi is not a test pressure. We are REVERSING osmosis, the natural tendency for a liquid with a low concentration to permeate through a membrane into a higher concentration thereby diluting it. We need to force the liquid in a high concentration (seawater salt) to pass into a low concentration ( the clean permeate) Osmosis is so powerful it pushes water from the roots to the tops of giant redwoods!

So you need the 800 psi to overcome the natural osmotic pressure of seawater. If the pressure is lower permeation will happen but more salt will be passed through too. RO elements are never 100% filters. They may be 99.8% for seawater at the right pressure. On glycol they pass 7%, and we use three stages to get 7% of 7% of 7% for the final discharge.

The rate of permeate discharge is not related directly to the feed flow in GPM. Slowing down the flow using a smaller pump at the same pressure will produce the same permeate rate, for a while. The concentration of salt left behind will be higher, more likely to precipitate instead of staying in solution, and there will be reduced flushing, all leading to fouling quickly.

Baldor premium efficiency motors are very good, and increasing efficiency to get a lower amp rating is a good idea and not too expensive at this size motor. I don't work with single phase motors much any more. If this were a 3 phase motor I'd put a soft starter on it. That would allow you to use almost all the horsepower of the generator because it would be easy to start he motor. You might look at using a 3 phase motor (cheaper, lighter and more robust) with an inverter GS2-23P0 $300 from AutomationDirect to run it from the generator. You could then ramp up the motor gently and exactly match the required pump speed too. They have great tech support, you could discuss this with them.

Gary H. Lucas
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post #25 of 26 Old 11-01-2010
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By the way, run that motor on 230 Volts if your generator produces it! Otherwise you'll drawing twice as much current on half of the generator windings and that will surely cause you trouble.

I once went on a trouble call (industrial electrician in a former career, this is #3) on the biggest sump pump I've ever seen in a basement, a 4" discharge! It was overloading the lady's backup generator every time it kicked on. IT was 120 volts, but the generator was 120/240. I installed a 240 to 120 volt transformer and used 240 from the generator and the problem was solved.

Gary H. Lucas
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post #26 of 26 Old 11-02-2010
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Anybody have any experience using the Pur 35 watermaker? I would be interested in this one, because it can also be used in manual-mode, albeit FAR slower and lotsa work. I think the sell for $1800, but much less used...just hard-to-find used.

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