Watermaker without a high pressure pump

Discussion in 'Sailboats' started by GoSlow, Nov 30, 2008.

  1. GoSlow
    Joined: Apr 2007
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    GoSlow Junior Member

    I was recently introduced to a watermaker manufactured by Schenker in Italy. The product seemed unique in that it did not have a high pressure pump, used about half of the normal amperage of a conventional machine, and was very quiet. I assume the demo model I saw is representative of the entire line however I have never heard of the company or the product. Is anyone familiar with these watermakers? I am US based and there is no dealer here so I am concerned about parts and support.
  2. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member

    Thanks for the post. I don't know anything about them.


    The world is a small place these days and international orders are often faster than local orders particulalry if the local dealer is out of stock.

    I think this is Charlies line so we'll see if we can summon an expert.

  3. DGreenwood
    Joined: Aug 2004
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    DGreenwood Senior Member

    The similarity with thehttp://www.spectrawatermakers.com/is uncanny. I suspect that is why they are not for sale in the US??? I don't see that their power consumption is much different.
    I have installed a number of Spectra Watermakers to great satisfaction. Just another option.
  4. GoSlow
    Joined: Apr 2007
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    GoSlow Junior Member

    I agree...very similar. I was not aware of the Spectra product. We have consistently installed Village Marine products. We have not been dissatisfied, however seeing the Schenker, and now the Spectra, it appeared there may be technology available I was unfamiliar with. Being able to operate the watermaker from the battery instead of DC inverted to AC seems to make better sense. Thanks for the feedback.
  5. StrandedMariner
    Joined: Sep 2007
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    StrandedMariner Steelboatsailor

    There are basically two families of RO watermakers. With and without energy recovery. The basic principle is always the same. You need to overcome the osmotic pressure between sea water and fresh water, and that means you have to push pressurized sea water through a membrane. Hence the name Reversed Osmosis'.
    If that high pressure is directly or indirectly achieved (a characteristic of most energy recovery systems) does not change anything on the principle.

    Energy recovery typically has a lower energy consumption, but also a higher degree of complexity (read: stuff that can break and/or needs regular replacement).
    From what I could see in the information on the web site of Schenker, their system looks indeed very much the same like Spectra's.
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  6. JesperW
    Joined: May 2006
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    JesperW http://journeyman.se

    I sailed 18 months with one of their 60l/min units.
    It was very reliable, and as the OP says produces more water per Amp hour than any others I know. I had it running of the 12V service bank, with individual switches for the pumps so I could run it at half speed if I wanted to.

    It has some kind of energy recovery unit that goes "thump" every five seconds or so, so I wouldn't necessarily call it silent, but then I don't have much reference, maybe other brands are noisier!

    It doesn't like bubbles in the incoming seawater, but recovers production quickly as soon as it gets bubble free water.

    The only quirk it has is that if you are unlucky when you turn it off, the thing going "thump" will stop in a bad position and refuse to restart. In this case you need to press a mechanical lever on the machine. Mine was mounted in a way that this lever was very hard to get at, which was a bad mistake :rolleyes:

    It produced superb water and never had any trouble or malfunction for 18 months. This was 4 years ago. I just saw their new units last week at METS, and the only thing that had changed was the color. I belive this points to a solid design.


  7. charmc
    Joined: Jan 2007
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    charmc Senior Member

    Hi, all,

    Thanks for the message, Mike. The original question posed by GoSlow, whether anyone has experience with these more efficient reverse osmosis systems, seems well answered by DGreenwood and JesperW. I have no personal experience with these companies; their products are smaller than the systems I normally design. Stranded Mariner accurately pointed out the major difference between these and other RO systems; the mechanism for energy recovery. The Clark pump is the only difference between the Spectra and Schenker systems and all other RO systems. The polymer RO membranes which do the actual separation of molecules are made by a relatively few chemical companies in the world, and are virtually identical regardless of manufacturer. There has been progress over the past 20 years in membrane chemistry, enabling current systems to recover as much water with 15-20% less energy input than older systems. Only a small portion of the water is "filtered" through the membrane surface, leaving the majority to be discharged, still under nearly all the pressure needed to overcome the osmotic pressure of seawater, typically around 900 psi/60 bar. Most energy recovery systems channel this concentrated waste stream through a turbine which powers another pump doing much of the work to increase the pressure of the feedwater, enabling the main pump to operate with less power. The Clark reciprocating piston pump appears to be significantly more efficient than a turbine, enabling even more reduction in power required for the main pump.

    Spectra claims to have invented the Clark Pump; I don't know anything about the two companies, possibly one is licensing the other. Ultimately, the decision for long distance passagemakers is to find the best combination of capacity, power consumption, cost, and reliability.
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