Understanding the Watermaker Equation

[witzgall]

Hi all;

I have ben futzing around on the internet researching watermaker parts and design. The Filmtec membranes of the 2.5x14 inch size variety take 800psi, and the output is 150 gpd. How much gpm will the high pressure pump need to deliver to push that much water through the membrane? Or put another day, what is the typical rejection rate for a Seawater watermaker?

Chris

[s/v Thea]

Dow has a software package you can download to design/rate watermakers:

ROSA

Doug

[GordMay]

The supply product ratio is ROUGHLY 10:1, so the 150 GPD (6 1/4 GPH) watermaker pump will require ABOUT 62 GPH.

[Tellie]

Gord is right a rough estimate is a 10:1 ratio.
I'm assuming you're intent is to design and build your own watermaker. So my question to you is why are you considering a 2.5"x14" membrane?

[witzgall]

I am trying to see what I can come up with on the lower DC draw side of things. Most likely, it is only an academic exercise, as it looks like even matching the gal/AH of the Katadyn's is hard to do.

Chris

Originally Posted by Tellie

Gord is right a rough estimate is a 10:1 ratio.
I'm assuming you're intent is to design and build your own watermaker. So my question to you is why are you considering a 2.5"x14" membrane?

[Tellie]

Originally Posted by witzgall

I am trying to see what I can come up with on the lower DC draw side of things. Most likely, it is only an academic exercise, as it looks like even matching the gal/AH of the Katadyn's is hard to do.

Chris

Yeah it would be very hard to do on a 12V home built unit.
Is an engine driven pump out of the question?

[witzgall]

No, engine driven is not out of the question - and the boat was cruised by the original owner with one. There is a PTO on the front, and he had a shaft over the engine to drive both a WM and refrigeration. Both are gone now, and I removed the shaft, but I could easily mount a pump on top of the engine driving it from the double pulley PTO.

Running the engine every few days for water would not be so bad, but I am trying to exhaust other possibilities before going that route. We have 240w of solar and soon a wind genny, so right now I think we are energy independent. Once we have it all up, and can spend some more days on the hook, I will have a better idea.

Chris

Originally Posted by Tellie

Yeah it would be very hard to do on a 12V home built unit.
Is an engine driven pump out of the question?

[Tellie]

Originally Posted by witzgall

No, engine driven is not out of the question - and the boat was cruised by the original owner with one. There is a PTO on the front, and he had a shaft over the engine to drive both a WM and refrigeration. Both are gone now, and I removed the shaft, but I could easily mount a pump on top of the engine driving it from the double pulley PTO.

Running the engine every few days for water would not be so bad, but I am trying to exhaust other possibilities before going that route. We have 240w of solar and soon a wind genny, so right now I think we are energy independent. Once we have it all up, and can spend some more days on the hook, I will have a better idea.

Chris

The nice advatage to an engine driven unit is you can make it big enough to make a lot of water faster with less operating intervals. Staying energy independant on 12V watermaker gets real hard without energy recovery. If you decide to build an engine take off let me know. I usally have a bunch of used spare parts that might help you keep the cost down, membrane vessels, valves etc.