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Old 07-06-2010, 21:21   #31
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Originally Posted by Brent Swain View Post
Pressure washer pumps work well. Just make sure they are over 3gpm and have ceramic plungers.
What if they don't have ceramic plungers? What other material would they be made from? The pump I listed has a 1.5gpm rate. Why is this too small?
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Old 08-06-2010, 07:49   #32
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Originally Posted by dennisail View Post
What if they don't have ceramic plungers? What other material would they be made from? The pump I listed has a 1.5gpm rate. Why is this too small?
Hi Dennisail,

Brent is right. The pump you posted above will let you down in very short order. Most of those inexpensive pressure washers ues aluminum pumps most of them are diaphragm type pumnps. They certainly are not up to the task of the demanding requirements a water maker will need. First off the rated flow and pressures are a bit exaggerated for those units. Even if they could meet those numbers I would expect that the pump would fail within the first hour of use adapted to a small salt water membrane RO system. They are $130 because they are cheap even for their designed use which might be short bursts to wash a car off. They use cheap plastic pressure valves and very weak seals and O-ring connections. Replacement parts for these units are often more expensive than the unit itself. Small RO systems that only flow those numbers will be required to run for hours at a time. These cheap pressure washer pumps just aren't going to stand up even once. If you are serious about building your own unit start with a decent pump like a CAT. It's true that water makers aren't rocket science, but they don't have any classes in rocketry school about water makers. There is plenty of info here and on the net about building your own from others such as Brent and myself who have built many. Ask and you shall receive.
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Old 08-06-2010, 10:13   #33
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Thanks Tellie. Here are some questions then How much does the cat pump cost? Does it have a motor? How much can I expect a fully operational DIY water maker cost me to build? I think the prices companies want for a complete unit is ridiculous.
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Old 09-06-2010, 08:32   #34
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Originally Posted by dennisail View Post
Thanks Tellie. Here are some questions then How much does the cat pump cost? Does it have a motor? How much can I expect a fully operational DIY water maker cost me to build? I think the prices companies want for a complete unit is ridiculous.

This post might be a bit controversial but it is from my personal experience. Take it for what it's worth, which isn't much.

Cat pump prices are easy to find on their website. It all depends on what you want and what size water maker you intend to build. A reasonable starting point would be close to $400 for the pump, no motor. Giant also makes an acceptable pump for less. Cat have pumps that are best suited for water makers but they get pricey quick.
As far as how much a DIY water maker will cost depends on what you want, what corners you're willing to cut and which ones others will that you won't, and what power you're willing to commit to run your DIY project and replenish that power. There are several DIY plans available on the net that can give you good ideas as to the cost of the basic materials. But two big questions often over looked. How good are your mechanical abilities and do you value your time? Ex. engine driven pumps are attractive but do you understand side loading issues with some marine engines? DC powered units will pull plenty of amps. Do you have them? How do you put them back for your boats other needs? AC driven units require inverters/generators. These are just a few simple questions that can add a few thousand dollars to your build before you start buying water maker parts and begin assembly. You may already have all this aboard. How much water do you want and how much do you need to make and in what time frame to keep your water maker healthy and operational? Some will poo poo the above but I have delt with all these issues and more before.
All that being said, I wouldn't discourage anyone who wants to build their own water maker from doing so. It can and has been done many times with information from the net and a few fine folks here. You can save some boat bucks to be sure. Just be a bit wary of "How easy it is" sometimes the simplest of things can get complicated and time consuming real quick. Real tangible costs could be $1500-$3500 depending on your McGiverability. Add your time for running down parts, fabricating brackets, buying a few items you didn't know you'll need for your particular application, the learning curve, and those prices can double.
Commercial water makers are expensive. I could write pages on the expenses companies go through to bring anything to market. Especially a small niche business as small water makers for cruisers but that could open a can of capitalistic worms here I'm not willing to debate.
My suggestion is to do a bit more research first. Check E-Bay for really cheap plans for DIY water makers, worth every cent. Ask here with any questions you encounter that arise. We'll help.
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Old 09-06-2010, 15:12   #35
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Thanks for that. My mechanical ability and McGiverability is excellent. My car I were recently featured on the cover of a magazine because I built it myself and made a crapload of power and fast quatermile times for very little money using alternative ideas. I had no real previous experience in doing engine conversions etc and just read what people had to say on forums like this (with large grains of salt) and came out on top.

A large part of doing something like this is finding out all the various ways to do it then pricing the parts and weighing advantages. At this stage I still need to learn a lot about these systems. There are so many pumps and motors out there I just don't know where to start. I would probably base my system around what motors and pumps will most suit my needs.

At this stage if I could find a cheap pump with an AC motor already attached, I would run it off an inverter. Hence my failed idea of a pressure washer due to reliability. Inverters seem to be cheap off ebay. (note I would also carry a 240v generator on board). I like the idea of electric as if my engine lets me down I can still make water. I realize it will tax the living crap out of my batteries. But in the event of an engine failure I will still have the ability to make water from renewable energy (albeit very sparingly) and I will have my 240v petrol generator.

Under normal circumstances I would size it so I can run it for an hour or so whilst my engine is running so my alternators are supplying the power rather than my battery banks. This may require the use of 2 alternators on my engine (which is a good idea for redundancy anyway). I would want to get enough water to fill my tank. I am looking at buying trimarans so I would have small tankage for reduced weight and fill the smallish tank every few days (prob around 100L).

How is my line of thinking so far?

Here is a list of membranes and pressure vessels.

Part Size (inches) Square Test Flow Stabilized Quantity Pricing (each)
Number Diam. x Length Feet PSI GPD Rejection
60. SW30-2514 2.5 x 14 61/2 800 150 99.4 $ 171
61. SW30-2521 2.5 x 21 13 800 300 99.4 $ 171
62. SW30-2540 2.5 x 40 29 800 700 99.4 $ 190
63. SW30-4021 4.0 x 21 33 800 800 99.4 $ 302

2521 1000 psi $219
2540 1000 psi $319
4014 1000 psi $-----
4021 1000 psi $369
4040 1000 psi $456

It seems the 700gpd version is a good price for the membrane $190. But it is 40" long. The 800gpd verison is only 21" long but it costs $302.

What sort of pumps would I be looking at for membranes of this size? IS there a percentage rating I need on the pump compared to GPH of the membrane? EG I need a pump that has 4 times the flow at 800psi of the product rate of the membrane?
Attached Files
File Type: pdf FilmtecPL.pdf (41.4 KB, 245 views)
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Old 09-06-2010, 16:35   #36
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My General TT911 pump cost me around $300, and works well.
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Old 09-06-2010, 16:48   #37
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How many GPD membrane would you use with a TT911? And what size AC motor would it require?
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