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Old 24-12-2019, 09:54   #1
er9
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reverse osmosis / desalination

ok so I have to admit im a bit confused on this topic.

if basic reverse osmosis desalinates sea water why are 'desalination units' like the katadyns so expensive when basic RO units only $200-300? why would we spend $4k on a Katadyn or comparable unit?
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Old 24-12-2019, 10:08   #2
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Re: reverse osmosis / desalination

The pressures required to desalinate saltwater are orders of magnitude greater than that needed to purify freshwater. Thus the need for higher quality parts and a much higher cost pump and membrane as well as much greater power demand to run it all.

How much freshwater do you want? Comparing a hand pumped survival type unit with one like our Sea Recovery 30 gallon per hour unit is apples to watermelons.
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Old 24-12-2019, 10:24   #3
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Re: reverse osmosis / desalination

interesting. i'm looking at a small portable katadyn for now but want to maybe play around with making a DIY RO unit at some point when I have the time. I thought I remember a thread on CF where someone was working on a DIY unit but cant seem to locate it.
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Old 24-12-2019, 10:31   #4
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Re: reverse osmosis / desalination

The pumps used in a RO unit are basically the same as used in pressure washers. Then you need a motor to run it, and 12v DC motors that strong are expensive. Then you need a membrane filter, which ain't cheap, then you need a way to flush the brine between sending loads of fresh salt water through the membrane, then you need a set of solenoid water valves, then you need a timing circuit to control all that, then you....

If you want to engineer your own as a very expensive DIY project, go for it, but don't expect to ever finish the job.
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Old 24-12-2019, 10:55   #5
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Re: reverse osmosis / desalination

Here is a place that sells DIY kits and parts. There are tons of YouTube videos on it also.
https://seawaterpro.com/
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Old 24-12-2019, 11:30   #6
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Re: reverse osmosis / desalination

If your going to build one I would recommend against DC, unless and maybe 1% or less of people do, have a truly massive DC system both in storage and charge capacity.
AC will require a generator, cause if you run one off of an inverter, it’s DC, just less efficient than DC direct, but it is an option if the generator is broken, just run the motor to operate the alternator to keep from slaying the bank.

Th power required to pressurized water to 800 PSI or more is often underestimated with simple pumps.
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Old 24-12-2019, 11:34   #7
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Re: reverse osmosis / desalination

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Originally Posted by Gtstricky View Post
Here is a place that sells DIY kits and parts. There are tons of YouTube videos on it also.
https://seawaterpro.com/
thanks for the link. those look like good quality affordable units.
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Old 24-12-2019, 11:38   #8
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Re: reverse osmosis / desalination

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Originally Posted by a64pilot View Post
If your going to build one I would recommend against DC, unless and maybe 1% or less of people do, have a truly massive DC system both in storage and charge capacity.
AC will require a generator, cause if you run one off of an inverter, its DC, just less efficient than DC direct, but it is an option if the generator is broken, just run the motor to operate the alternator to keep from slaying the bank.

Th power required to pressurized water to 800 PSI or more is often underestimated with simple pumps.
wow! 800 psi? ok now its starting to make sense.
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Old 24-12-2019, 11:52   #9
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Re: reverse osmosis / desalination

Kits are doable. I made my own a couple times, Once with a Cat pump and system from a 120V unit. Mounted on the engine. 25 gal per hour.
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Old 24-12-2019, 12:41   #10
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Re: reverse osmosis / desalination

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wow! 800 psi? ok now its starting to make sense.
Plus or minus, lower is lower output of course and I believe the membranes are good for 1,000 PSI.
But then you need to remember that to keep the membranes flushed clean you have to pump roughly three times as much water at that high pressure than what you make.
I believe my pump is 1.6 gpm to make 1/2 gpm of fresh water. Salinity and water temp will vary that number by a significant amount of course.

Dont get the required amount of water and your membranes will not last long of course.
Id look for a book that discusses watermaker design if you can find one for smaller units.

They are actually very simple systems, but the components if you use quality ones will cost you more than you may think.
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Old 24-12-2019, 12:57   #11
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Re: reverse osmosis / desalination

I've built several watermakers. But in learning, wasted a lot of money. If I was going to build another system, I'd buy one of CruiseRO's. My current 40gph is similar to theirs.

Yacht & Boat Water Maker by Cruise RO Water & Power
While I can build a cheaper watermaker now, my first one, by the time it was reliable and I didn't ruin membranes, cost at least double. And there's a lot of searching for all the parts, gauges, flow meter, high pressure plumbing, and so on.
Another thing to remember, membranes are rated at 77F. Colder sea water means less fresh water.
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Old 24-12-2019, 13:41   #12
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Re: reverse osmosis / desalination

They are simple systems if you are willing to adjust manually. But yes $ add up.
One thing to keep in mind is pump material. Salt water sitting in the cylinders of a pump can do damage... unlike a common pressure washer that is used for fresh water. Either may have a Cat brand pump, but they may not be the same material.
I was able to find a 12V clutch readily for my 120V water maker conversion to engine drive.
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Old 25-12-2019, 09:09   #13
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Re: reverse osmosis / desalination

Are not expensive to make compared to the retail units , your most expensive part in the CAT pump , everything esle can be found in Ebay or your local hardware shop, and then the parts are cheaper as well , a decent DIY skill set can create your own
this link is from YBW forums in the UK were cruisers built there own and plenty of YOUTUBE videos to make it ,
cost around $1500 to make compared to the $4000 + units advertised , and as you built it you can repair and replace with confidence,
https://forums.ybw.com/index.php?thr...-maker.505461/
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Old 25-12-2019, 09:42   #14
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Re: reverse osmosis / desalination

Quote:
Originally Posted by er9 View Post
interesting. i'm looking at a small portable katadyn for now but want to maybe play around with making a DIY RO unit at some point when I have the time. I thought I remember a thread on CF where someone was working on a DIY unit but cant seem to locate it.
This is the guy you want to talk with basic systems reliable, best pumps..
cant say enough about him, answers the phone, answers email... easy to repair your self ..... Best bang for the buck...

http://sunpurewatermakers.com for boaters...
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Old 25-12-2019, 14:08   #15
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Re: reverse osmosis / desalination

I'll second the nod for CruiseRO watermakers. All the stuff is off-the-shelf (NOT manufacturer-specific), support is great, and the system works! You assemble and install, so you know the system, and can repair/tweek it as required. Ours is a 2015 30gph, and today produces 36-38gph!
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