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Old 08-10-2010, 09:39   #196
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Just to reiterate you need a pressure gauge. I cant remember seeing any mechanically driven RO without one.

Secondly an "Unloader" valve will not work if used in the normal way. remember you must generate "back pressure " for the membranes to work, an unloader is a relief valve there is no restriction to flow until "something " else generate a high back pressure, like shutting off the washing lance trigger.

You could however plumb an unloader or bypass regulator into the output of teh membrane so that the flow is effectively through the normally closed route through teh unloader. Then it would act as a back pressure regulator, you would "cap" the normal output of the unloader and the brine exists via the relief outlet. Some unloaders however have a full flow action where upon on unloading the valve springs fully open, this type will not work well as a back pressure regulator.

NOte if you have a fairly constant flow through the watermaker, ie you are driving it from a constant rpm source, then a simple needle valve will act to provide back pressure. Thats what most RO makers use. Engine driven pumps need a good quailty back pressure regulator.

Of course for safety you also need an unloader ( relief) valve after the pump outlet set to 1000psi to protect the pump and the membrane from excess system pressure.

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Old 08-10-2010, 14:30   #197
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Originally Posted by Yachts66 View Post
After reading the posts above some seem to think such things as pressure gauges superfluous.

Thanks,

Thomas

Thomas---

Is that little guy whistling "Dixie?" I plan to use flow gages and an load pressure gage plus a vacuum gage on the pressure pump's input. That should give alert to change the filters.

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Old 08-10-2010, 14:32   #198
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Dave--

GOOD POST!!!

Foggy
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Old 11-10-2010, 14:22   #199
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Does anyone know how RO will work with intermitent flow, say pressure for a few minutes then no pressure then pressure angain? and if I size it small enough to run 24 hours a day how offen do you need to flush with fresh water?
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Old 11-10-2010, 14:52   #200
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Does anyone know how RO will work with intermitent flow, say pressure for a few minutes then no pressure then pressure angain? and if I size it small enough to run 24 hours a day how offen do you need to flush with fresh water?
Just barged in. Haven't looked at previous posts yet so forgive me if I am missing obvious things here...

Letting the pressure drop to 1 bar fast and lletting it rise back to 50 bar fast, is not a good idea. That way your membranes will not have a long lifespan.
One should increase/decrease pressure slowly. I always take some 30 seconds to get slowly from 1 to 50 bar (DIY, AC, Catpump-based, 2 membranes, 55 gph) and back.

Running 24 hours a day sounds interesting. What kind of system? Engine or AC driven hp pump? In that case you are facing extended periods of time with corrosive saltwater in your manifold.
Flushing would be obsolete cause you are not building any growth that you want to get rid of.

But give some more info on your system first.

Cheers,
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Old 12-10-2010, 06:44   #201
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Does anyone know how RO will work with intermitent flow, say pressure for a few minutes then no pressure then pressure angain? and if I size it small enough to run 24 hours a day how offen do you need to flush with fresh water?

Intermitent pressure should not be a too big of an issue. Sheneker and Spectra water makers create intermitent pressures in their operation. Where you might get into trouble is the flow. I too would be very interested in what design you are considering. The bigger issue maybe intermitent flow. Flow inrush can be more damaging if not properly regulated. Also I get the idea that this is gong to be a very small unit because you want to run it 24 hours a day. If so you need to provide enough flow. It's always pressure and flow that run hand in hand. Creating pressure is the easy part. Creating flow and pressure in the right combination is more difficult part.
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Old 12-10-2010, 06:57   #202
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Also flushing is sometimes misunderstood. While you are running your water maker it is constantly being flushed. As long as the pre-filters are doing their job you are keeping the membrane clean. Flushing with fresh water is only an attempt at clearing out as much sea water as possible so the unit can sit for a short period of time without use. Fresh water shouldn't contain as much small life forms in it as does salt water, but most people have no idea what is growing in their tanks that can start problems. When a water maker sits for a day or two these small animals die. When they die biological growth occurs on the dead remains. It is the fast bio growth that clogs a membrane. So a water maker that runs 24/7, like many commercial watermakers do, won't need much if any flushing. But water makers on boats are a whole different ball game with a whole new set of issues to deal with that 24/7 commercial units just don't need to worryabout.
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Old 12-10-2010, 14:03   #203
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I was thinking of something similar to the Spectra Clark pump with a bit larger cylinders, say 8 inch with a 1 inch shaft, so it would have a 60:1 pressure boost and using a low pressure pump to drive it, I would need 14 psi, 32 feet of head to drive it, with a large flow, 80 gph, without having to flush I could just size it for daily usage, and it would give the membrane a 60:1 flush.
I'm still trying to work it out in my head, down to mostly valves now that pressure fluccuations are not much of an issue
My other thought was to get a small high pressure pump and a circulator pump that will recurulate pressuized water through the membrane and pump in discharge a small amount of water out of the system to keep the salinity from going to high, say pump in 4gph and drain 3 1/2gph the other 1/2gpm goes through to become fresh water.
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Old 14-10-2010, 13:07   #204
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I do not know what the parts add up to now a days - but I do know the prices of complete R.O. units from the major manufacturers has gone up in price from 3x to 4x the price I paid 8 years ago. They are now considered a must have piece of equipment on modern cruising boats instead of a novelty nearly a decade ago so the prices have gone up as demand has increased.

That makes D-I-Y units attractive.
My DIY 540 gallon per day watermaker cost me roughly $700
No complaints.
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Old 14-10-2010, 18:10   #205
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Geez Brent, I spent that much just on a brass pump and a 2HP motor. On top of that, I just purchased a SS pressure transducer to measure the membrane pressure. Chalk up another 125+ shipping.

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Old 14-10-2010, 21:46   #206
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In Australia, I have puchased a petrol powered, brass pump pressure washer from ebay $400.00. A pressure gauge and regulator $150.00, 2 x Filmtec 2 X 2 1/2 x 40 inch membranes and fiberglass housings $1,000.00. Just a bit of plumbing and I am set to test it.
Under $2,000 and I should get 300 litres/hour
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Old 15-10-2010, 08:12   #207
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In Australia, I have puchased a petrol powered, brass pump pressure washer from ebay $400.00. A pressure gauge and regulator $150.00, 2 x Filmtec 2 X 2 1/2 x 40 inch membranes and fiberglass housings $1,000.00. Just a bit of plumbing and I am set to test it.
Under $2,000 and I should get 300 litres/hour



Hi beau,

I hope you don't mind my .02 cents. It's meant with only good intent. Your post above sent off a few red flags for me. I've seen this before in real world applications. My comments are made in general and are NOT directed at you. These are just observations on the small post you made above that can be applied to others who want to take a DIY water maker project on. Like others have said, it is not rocket science. But even a rocket scientist can get into costly mistakes if he doesn't have enough information about things that are not rocket related.


Your figures are either a typo or a miscalculation. I'm guessing a typo but for fun let's say it's a miscalculation. If it were 30 liters per day (8gpd) or 300 liters per day (80gpd) the water maker would be very anemic and the two 2540s would foul in short order. If it is 300 liters per hour as posted (79 gph/1900gpd) it would be very impressive. For a short period of time. Filmtec 2540 membranes are rated for 700gpd production and 6gpm flow in perfect conditions. Pushing them to 300 liters/hour would mean you would have to get 950gpd from each. The excessive pressures and flow needed to achieve that rate would send the membranes to an early demise. The pressures inside the membrane vessels would well exceed the 1000psi limits, pressures that many side walk cleaners can easily produce. Many vessels will not take these pressures and in time will burst. Also in your short list of materials you have left a few items out. What about a boost pump? You will certainly need one capable of delivering the volume of water a pump of the size needed to drive two 2540s will demand. Ceramic plungers will over heat in a matter of moments and will crack with a small amount cold sea water inrush. The energy used for the boost pump is a calculation that should be considered as well. You also don't mention the anticipated costs of good quality high pressure hoses and fittings. Will you use SS fittings attached to a brass pump? A $400 pump off of E-Bay, is this a new pump along with the gas motor to drive it? Are you planning to run a gas engine below decks? Most people won't. If not how will you drive the pump? Engine take off or electric motor. Those considering not using a gas motor below decks will need to consider the added costs of an electric motor capable of handling a pumps demand to feed two 2540s and the associated electrical needs. If it is an engine take off, what about a 12V clutch? They're not $20 a pop either. What about a PTO pulley if either the engine does not have a spare available or you need an extra groove to drive a twin belt clutch. What about an engine mounted bracket to bolt your pump to. A dedicated forward facing through hull deep below the water line would be highly recommended for a water maker of this size. At least 3/4" in size, a 1" with a good ball valve would be preferable, if you have one unused on your boat great, many people don't. How large are your fresh water tanks? Not only will you need to run your water maker a few hours at a time to keep the membranes healthy you'll need to take back enough fresh water made to give your water maker a fresh water flush after each use. Figure at least a five minute run with most water makers, probably more because you are using brass. Figure the flush flow at 6gpm. With a water maker of this size a boat should have fairly large holding capacities. Anything under 100 gallons and in my opinion this unit is too big for the boat. These are just a few things that people run into when building their own that they may not have anticipated. I never, never discourage anyone from this project. But if anyone thinks that it is just a membrane, a high pressure pump and some plumbing fittings you really need to study a bit more first or chances are very good that you will be disappointed. Water makers, even home built ones are expensive. What is good for one is not going to be good for the next. Buying or building the wrong one with too little information happens too often.
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Old 15-10-2010, 16:03   #208
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Any pressure washer pump with ceramic plungers, which can put out at least 3 GPM, is fine for a water maker, and is far more ruggedly built, for much higher pressure than a watermaker will ever use.
They can be found for under $3
Italian made ones are the best.
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Old 15-10-2010, 16:36   #209
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Any pressure washer pump with ceramic plungers, which can put out at least 3 GPM, is fine for a water maker, and is far more ruggedly built, for much higher pressure than a watermaker will ever use.
They can be found for under $3
Italian made ones are the best.
Mind sharing your source Brent...you can PM me if you'd rather.
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Old 15-10-2010, 18:46   #210
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Tellie, i appreciate your comments and support.
I have been told I can get 40 gallons per hour of fresh water from 2 x 2 1/2 X 40 inch membranes in series and yes 40 US gallons is 150 liters, my mistake.
yes, I have a 12 v boost pump which cost $65.00.
The pressure washer is 6.5 Hp driving a Brass (italian designed pump) max pressure is 3,500 psi. of course I wont be using more than the 800 -1000psi.
the gasoline motor will be run outside (of course)
i have a complete spare pump which cost $150.00, a full set of seals etc cost $35.00.
I am replacing the original plungers with ceramic ones.
http://www.westward-ii.com/PDF's/How...watermaker.pdf
Is the design I am using.

I appreciate your comments and support
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