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Old 20-10-2010, 15:32   #1
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Engine-Driver Watermaker

Hi all,

I would like to build an engine driven watermaker based on Brent's TT9111 pump.

Here are a few questions:

1. The pump is rated at 1500 PSI not 2500 as Brent stated in one of the posts. Is this still okay?

2. How do I avoid the electric clutch? I like to go simple.
3. I spoke with one watermaker manufacture who said that his design will work with RPM of 1200-2200. How can you have such a wide rpm?
4. The priming pump- go 12v electric? or??

Thanks,

Mike
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Old 20-10-2010, 18:00   #2
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You only need 800psi. Plunger pumps output is a direct relationship to RPMs. If the pump is outputing 3 gallons/minute at 1000 rpm, it will output 6 gallons at 2000 rpm. Pressure will be what ever it needs to be to move the fluid or up to the point where the driving force cannot tunr the pump shaft, the pump's regulator limits the pressure or the pump destroys itself. But something must give.

Remember, HP = pressure*flow/1460(or so) So if the engine's rpm changes the gallons of output will change along with the HP needed to turn the pump. Better check the limits of the membrane you plan to use. That will set the limits of rpm.

Personally, I would not venture down the path to an engine driven watermaker ..........but never the less, they do work.

Foggy
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Old 21-10-2010, 19:23   #3
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Mike

system operating pressure is set by the back pressure regulator, placed after the membrane. If the pump is revolving at a fixed RPM, then a simple needle valve will act as a pressure valve.( other wise a proper back pressure regulator is needed like teh CAT 7070) The system will also have a relief valve set just above the normal max woorking pressure ( usually its the membrane thats the limit) , this is typically 1000 psi. The working pressure is from about 700 to 900 psi depending on water temp and salinity.

I wouldnt reccomend an engine driven unit, either.

My advice is either build a 12V DC version which in reality is limited to about 1HP, whoch gives around a 2G/minute watermaker hence about about .3GM product flow or about 18G/H. For this size to work you need to be able to let it run for some time. But its the most versatile system and regular long runs are better for teh membrane. However 1HP is a big current draw

AFter that its a AC system, with 2 or 3HP motors.

I dislike engine driven units, firsly the mounting of teh pump can be difficult, secondly there is the need for mechanical clutch and the whole thing is subject to vibration, not to mention the problem of 800psi leaks of saltwater in the engine bay. Again the engine mounted one limits the pipe runs to the membrane so it has to be mounted close by.

Dave
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Old 21-10-2010, 22:56   #4
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Dave,

I was looking at building a 12V system but at around 10GPH with around 25Amps!!! I woulld need to run this for 2.5 hours per day to meet our water needs. I do have 525W of solar but still, 60-70 extra AMPS is a lot. I will need to run the engine to help the solar panels therefore I was thinking about an engine driven system
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Old 21-10-2010, 23:19   #5
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I second and third the above belief on engine driven water makers. Main engine driven water makers are not for the typical cruiser that I've come in contact with. Do they work? Sure they do. But you need to be intimately knowledgeable about them. Your few questions alone bring up many issues. Plunger pumps as foggysail and goboatingnow state will produce differently at different rpms. It's always about flow and pressure. The system you describes life will depend on very good pressure regulation. A simple needle valve set to create 800psi inside the membrane vessel will be it's undoing if your rpms double. The pump will create more flow and the water will still try to escape through the needle valve set at a lower flow. It's the same principal pressure cleaners use. Increase the flow and the pressure rises dramatically the smaller the opening is. So if you increase the rpms without opening the regulator at the same time the pressures will increase beyond the rated 1000 psi the membranes and membrane vessels are rated at. You can ruin the membranes, burst the vessel, hoses and fittings spraying salt water all over. I would not avoid the clutch. It is the one switched part you can instantly shut off at a distance if something goes wrong. The boost pump is important to make sure the high pressure pump is fed properly. For the most part they are always a 12V constant run pump. Not a cheap intermittent pump. I don't know which manufacturer you spoke to. I have a good idea, but be careful, they are trying to sell you their stuff. Up front most members know I'm a water maker dealer. I only give general advice on the board. My advice is to search all the water maker threads here on Cruisers Forum. There is a ton of information about water makers. Several members have or are building their own as well. They love to relate their experiences and are willing to give advice as well.
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Old 22-10-2010, 13:09   #6
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Tellie,

Thanks for the input. I don't have much knowledge on watermakers but can sure build one once I understand it.
I appreciate your input on this and, yes I know your are the Spectra dealer.

I also like Brent Swain's approach (In general) to make life simple.
We are 2 on board and like to shower everyday. Our boat is setup with 525W solar, 110Amp Alt. And 1080 Amp/H Batteries.
I will be upfront too and will say that I will not pay $5000-6000 for a Spectra. Not because I don't think they are worth it (although some people look at the parts cost running around $2000 they forget the front end R&D that goes into the product and the back end like customer support and warranty) I just want to build my own.
Looking at the other 12V that people here did, the AMP count is around 29 amps per 8-10 Gal. I would need to run this setup for 2-1/2 hour per day. I don't think my solar will handle that plus my other 12v systems like fridge/ ssb etc.
This means that I will have to run my engine, therefore I was in agreement with Brent.
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Old 22-10-2010, 17:49   #7
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Quote:
Originally Posted by wingover View Post
Tellie,

Thanks for the input. I don't have much knowledge on watermakers but can sure build one once I understand it. I appreciate your input on this and, yes I know your are the Spectra dealer.
I also like Brent Swain's approach (In general) to make life simple.
We are 2 on board and like to shower everyday. Our boat is setup with 525W solar, 110Amp Alt. And 1080 Amp/H Batteries.
I will be upfront too and will say that I will not pay $5000-6000 for a Spectra. Not because I don't think they are worth it (although some people look at the parts cost running around $2000 they forget the front end R&D that goes into the product and the back end like customer support and warranty) I just want to build my own.
Looking at the other 12V that people here did, the AMP count is around 29 amps per 8-10 Gal. I would need to run this setup for 2-1/2 hour per day. I don't think my solar will handle that plus my other 12v systems like fridge/ ssb etc.
This means that I will have to run my engine, therefore I was in agreement with Brent.

I like Brents take on things as well. I enjoy his other subjects and his back to basic KISS approach on cruising. His posts convinced me to go with a composting head. I couldn't be more happy that I did. I've said here before that I'd like to see his work shop, I'm sure I could spend hours there. Good luck on your build and keep us up to date as you go along.
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