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  #11  
Old 10-06-2009
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GREAT thread, guys.

- CD
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  #12  
Old 10-06-2009
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Quote:
Originally Posted by geraldartman View Post
Glad I sail the Great Lakes. $70 filter will handle a couple of hundred gallons. Have to hand pump though.

But you have a 'special' problem on the GLakes .... cryptosporidiuim - a very nasty oocyst that can be easily taken onboard from water distribution sources that dont have the proper filtration on them. Crypto is resistant to chlorine sanitization ... so you really have to be sure to filter any 'questionable' water you take onboard - with a 'FDA certified' filter that is 'validated' to remove 'cysts'.
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Old 10-06-2009
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Quote:
Originally Posted by night0wl View Post
This project has me intrigued. What is a good source (online or otherwise) for membranes and membrane housings?
Actually membranes are not difficult to source. Along with the other suggestions, try here

FILMTEC Membranes

Coincidentally, I am busy building a water maker as we speak. I have a piece of stainless tube and the membrane and am now busy with machining the end pieces to locate the membrane, provide the water/brine seperation and attach the hoses for water in and out.

I have a 110v inverter and a genset (not in yet) so I will be running off a 110v motor for the pump. This gives me the best of all worlds. I can run on shorepower, I can run it while I'm motoring (large-frame alt puts out 180amps) or I can run it off the genset.

As far as raw water supply, I have thought about teeing into another skin fiitting and for reasons already espoused on other posts, I'm nervous of the possibility of other appliances drawing water away from the pump because the engine and/or genset will probably be running at the same time. The answer for me is to T off one of the head inlets.

Good post. Thanks
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The rule of thumb on water makers is to put the thull as far forward as practical to lessen the liklihood of contamination - like from the sink, for example or God forbid the head.

- CD
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That is a good article, I build RO systems, for wastewater not clean water. A couple of comments.

I prefer the BlueWhite flowmeters over the Dwyers. They have union ends that make swapping or cleaning the flowmeter much easier. They also come in elbow end style that is very easy to mount.

The Wanner pumps mentioned are very good. They are hydraulicly driven diaphram pumps in an axial configuration. All the moving parts run in an oil bath and they are very tolerant of abrasive or aggressive fluids. They are MUCH quieter than piston pumps, and have much less vibration. Both very good on a boat.
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I'd like to add one other thing about safety. The PDF file showed two Y valves used in the feed and permeate lines. Those are good choices, but it is important to know why. The author mentions that the brine line after the control valve and the permeate line are both low pressure. That's true, only if nothing ever blocks them!

I've had three high pressure RO explosions in the past five years. One because someone plugged a drain line that the relief valve was plumbed into. One because two 2-way valves were used instead of a no-center-off 3-way valve. Finally, because the permeate pipe froze, and so did the two relief valves!

So don't be tempted to go adding lots of 'convenience' valves to this design!

Gary H. Lucas
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Gary

I intend to have my brine line going out above the water line to prevent it cloggng with sea life etc and to save having another below waterline skin fitting.

On the permeate line I intend to build a stainless manifold. I have three tanks so I want to have the manifold equipped with obviously an incoming line from the membrane cylinder and then four valved outlets. One will go to a sampling tap to be able to ensure that the water is good before sending it to a tank. The other three will go to each of the tanks so that I can fill the one that needs it.

On this manifold I will also put a relief valve that will vent at about 200PSI to prevent any pressure build up if something goes wrong downstream or if all 4 valves are accidentally turned off.

Is this OK or am I over-killing the thing?
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Old 10-07-2009
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I'd try to do it without the relief valve, by running the permeate into a vented tank or open top PVC standpipe, then gravity flow through 4 inexpensive plastic valves that will see no pressure. You want to maximize your clean water production and backpressure on the permeate lines always reduces it.

Another interesting thing. Membranes will produce poor quality water if run at too low a pressure. You can get water out of a membrane at almost any pressure, but the water will be the highest quality when the pressure matches the membranes design pressure.

If you take your boat up a river into fresh water you'll find that the RO will produce a lot more permeate at a much lower pressure, like 300 psi. You wouldn't want to run it at 800 psi because the flux rate (permeate flow) would be way to high and you'd run the risk of fouling the membrane.

One last thing. When the differential pressure from the feed end to the discharge end starts to increase you have fouling going on. The membrane should be cleaned immediately, or you run the risk of never being able to clean it. If you clean it and the differential pressure is still high you didn't get it clean, and another immediate cleaning is warranted. Often you need to change cleaning chemistries, because the foulant may be something you weren't expecting. Membranes have a bad tendency to get into a death spiral. One bad cleaning leads to another until the membrane is shot. On a boat you are talking $100 to maybe $700. On our systems it is more like $10,000!

Gary H. Lucas
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Old 10-08-2009
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Quote:
Originally Posted by GaryHLucas View Post
I'd try to do it without the relief valve, by running the permeate into a vented tank or open top PVC standpipe, then gravity flow through 4 inexpensive plastic valves that will see no pressure. You want to maximize your clean water production and backpressure on the permeate lines always reduces it.
Gary, seems my "layout" wasn't that clear. The permeate would flow into the manifold and four valves (taps) which would allow me to direct the flow (not under pressure) to where I want it. The relief valve is simply to ensure that I don't accidentaly pressurise the inside of the mambrane by shutting off all 4 valves.

Quote:
Originally Posted by GaryHLucas View Post
One last thing. When the differential pressure from the feed end to the discharge end starts to increase you have fouling going on. The membrane should be cleaned immediately, or you run the risk of never being able to clean it. If you clean it and the differential pressure is still high you didn't get it clean, and another immediate cleaning is warranted. Often you need to change cleaning chemistries, because the foulant may be something you weren't expecting. Membranes have a bad tendency to get into a death spiral. One bad cleaning leads to another until the membrane is shot.
The system I am contemplating has only one presssure guage - on the brine line at the output end of the membrane (to adjust the pressure on the high pressure side of the membrane). How do you know that a differential pressure exists? That implies two pressure guages. Please explain the setup as you see it.

Thanks
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  #20  
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I understood your layout, I was just suggesting that the manifold could be an open vented tank so you don't need the relief valve. The flow rate is so low it would never fill the tank unless your lines were really tiny.

Yes, I would put two pressure gauges, one on the feed end one on the concentrate end. You want some pressure drop across the membrane. If there isn't any pressure drop then there isn't any turbulence and it will foul rapidly. There is a minimum GPM through flow for each size and type of membrane. So the two gauges tell you that you have sufficient flow, and then that the membrane is fouling.

Gary H. Lucas
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