Running freshwater through your WM, could this cause problems?

[autumnbreeze27]

I was talking with an engineer on a megayacht, and he runs his freshwater through his watermaker to get the PPM down very low (close to 0). Makes it easier to keep the boat sparking clean.

A very knowledgeable source told me to never run freshwater through the membrane at pressure, that it would damage the membrane.

I'm looking for other input on this. I'm thinking I could use the freshwater flush setting and really clean the water... I know that it's good to have some stuff in the water for drinking/health reasons, so I don't want to argue the merits of 10 PPM water, I just want to know if I risk damaging anything if I do this? Our watermaker usually produces water in the 280 ppm range, but I've turned it on before when I still had freshwater in the system and seen very low numbers. We always fill with dock water before leaving the dock, and sometimes that water isn't the greatest and I'd like to filter it more than the 2 micron I'm using now.

Our watermaker is a village marine little wonder VIP200.

Also the manual says never run freshwater over 35 PSI through the system with flushing. My freshwater system is 45 PSI and I usually either use the valve or open other fauces to reduce the pressure when flushing. Would 45 PSI really damage the membrane? Seems kinda silly to me since it's pushing water at 800 PSI?

[a64pilot]

Ask a manufacturer, but if you have the pressure right you can run fresh water through, as long as there are no chemicals especially chlorine in the water.
For washing the boat or similar, I'd get a de-mineralizer as that sounds like what you are after. There are filters for washing cars just for this purpose, not filters so much but de-mineralizers


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[s/v Jedi]

You can but must adjust pressure to stay within membrane maximum product output, which will be around 200psi.

[a64pilot]

Watch this, it may help

https://m.youtube.com/watch?v=aVAE5ZOKWAk

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[a64pilot]

Sorry it's this one
http://youtu.be/Ht2B3lpFbdQ


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[SV THIRD DAY]

Originally Posted by autumnbreeze27

A very knowledgeable source told me to never run freshwater through the membrane at pressure, that it would damage the membrane.

If you have the ability to manually adjust the system pressure on your water maker, then you can indeed run the standard sea water membrane on 100% fresh water. The IMPORTANT part is that you do not do it at 800psi, but rather only increase the system pressure until you reach your rated output, which will happen about 200-300psi.

The 800psi is the pressure needed to overcome the osmotic pressure of sea water and drive some fresh water through the membrane. But with no salt in fresh water, the osmotic pressure is MUCH less, so water will flow through the membranes at a much lower PSI. In fact, at 800PSI more water will want to flow through the membrane than the molecular pores in the membrane can handle and KA-POW...you can rupture you membrane.

Now one more thing to watch out for.
There had better be NO Chlorine in that tank water or another disaster, because Chlorine will oxidize the active layer of the membrane and KA-POW...another way to kill it.

Pure sea water 800PSI
Pure fresh water 200-300PSI

But what happens if you are in some unknown brackish water?
Easy...just slowly increase your system pressure until you reach your rated product water flow and stop, you will not risk your membranes at that level and can make all the water you want.

Oh and who is that ugly guy in the video...he does have a nice boat however....

[Tellie]

autumnbreeze27 What your engineer friend was more than likely talking about is a "Double pass " system. These are becoming more and more common these days in the mega yacht class of boats. Basically they are what they sound like. They pass dock water through either a SpotZero type or similar system to pre-treat the dock water before it then passes through the yachts watermaker before it is sent to the fresh water tanks or a separate dedicated holding tank meant solely for washing the yacht. Water that has been double passed is extremely clean and void of minerals, like calcium, lime, etc., those particles that leave spots on the yacht when it is rinsed down after washing. On large yachts this can save huge amounts of man hours wiping and buffing down the boat and more importantly reduce the wearing down of the finished surfaces of mega yachts. These systems reduce huge costs in maintenance and man hours alone and make double pass systems extremely cost effective for the big boat crowd.

Halden Marine Services | Marine Watermakers, Solar Panels, Wind Generators

[Tellie]

Originally Posted by a64pilot

Sorry it's this one
http://youtu.be/Ht2B3lpFbdQ


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Sorry is right! I almost fell backwards off my chair!

Just Kiddin Rich.


Halden Marine Services | Marine Watermakers, Solar Panels, Wind Generators

[autumnbreeze27]

I have a nut that regulates my pressure, would be nice to get a plastic piece made to fit over it to make it a tool free adjustment; anybody ever seen those online? Otherwise I'm thinking starboard and an afternoon with the dremel, but with my luck there won't be room in the housing. Anyhow, thanks for the explanation; we had a water softener at the dock but sold it when we left to cruise.


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[Paul L]

Originally Posted by autumnbreeze27

I have a nut that regulates my pressure, would be nice to get a plastic piece made to fit over it to make it a tool free adjustment; anybody ever seen those online? Otherwise I'm thinking starboard and an afternoon with the dremel, but with my luck there won't be room in the housing. Anyhow, thanks for the explanation; we had a water softener at the dock but sold it when we left to cruise.


Sent from somewhere in the Pacific

My Little Wonder uses an Allen key on the pressure regulator. I just leave the key in place.

[autumnbreeze27]

So I'm thinking about filling my stb tank, 100 gallons, and then run that through the watermaker to the port tank.

So that will likely take 10 hours still, since I have to run it at it's rated flow? and how much water will it put overboard? Any idea?

I may try this today. But if anybody has any experience with it I'd appreciate any insight.

I checked the manual, I didn't see anything about this procedure. I will check to see if there's a rated max flow for the membrane. It's a double small membrane, I think they're custom.

[SV THIRD DAY]

The answer depends on what water maker and RO Membrane you have.
Perhaps your membrane has additional rated fresh water output that your normal production rate is not getting due to the Hp pump size. So before giving you advice that could literally Damage your system....we need some additional details. The safe way is to just not exceed the rated output and that would be my answer without knowing more details.

[autumnbreeze27]

I checked the whole manual and it doesn't specify that info.

The closest I can get is looking at the temp correction factor chart. Uncorrected product flow is 5.67 gph, at 1C the TCF is 3.64, so that's 5.67 * 3.64 = 20.6 gph

Since the gauge only goes to 10 or 12 I guess I'll have to time how long it takes to fill a 1 gallon jug and do the math. (3 min per gallon)

Or does that not work because I need to take the actual temp of the water? The water is about 78, that TCF is 1, which means I'd only be making 5.67 gph, but I usually still make 8-10 gph.

[SV THIRD DAY]

Need brand of water maker and size (length and diameter) of RO Membrane. Get out of the technical weeds...you are overthinking with the temp issue, all we care about here is the Maximum rated flow rate of your RO Membrane and if we know the size of the membrane we can figure that out.

[autumnbreeze27]

I've got two 2.5" x 19" elements, membrane type is thin film composite

Note: water from Marina Vallarta that is in the tank right now is 160ppm after going through a 2 micron filter that turned dark brown. Water from the marina in barra is 360ppm after going through the same filter, it hasn't turned color yet (after 20 gallons), and it's reported that this water will stain stainless steel sinks if used regularly.