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Old 24-10-2019, 12:25   #1
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Small watermaker 3 gph

I am sharing my 3 gph watermaker design for those who want to DIY. After many months of experimentation I settled on the following design:

Parts
- Pumptec 116C stainless steel pump/motor combo. Make sure you order the .105 CAM which gives you around 15 gph total flow. The cost is substantially less than $500, feel free to negotiate with distributors but I can't disclose the actual discount I am getting.

http://www.pumptec.com/media/downloa...8215_80940.pdf

- Fiberglass pressure vessel and membrane from HCTI. The company is very easy to work with and they have great prices, expect to pay less than $400 for the pressure vessel and the membrane. I am using the 2514 size but I believe the 2521 could work as well.

HCTI - Vessels

The rest is fittings, pressure hose, a simple needle valve and a pressure gauge. You should aim to obtain all parts for less than $1,000.

Design
Salt water goes from intake to a strainer, 20-micron filter and then to the pump. The pump has three inlets and three outlets. Plug the four that you do not need. The pump output is attached directly to the pressure vessel (to minimize the number of connections). The high pressure output from the vessel goes (via a suitable length hose) to a t-connector that has a 1,500 psi gauge on one end and a needle valve on the other end. After the needle valve you can use common low pressure hose and fittings.

For extra safety, you can get a 1,000 psi pressure switch that can be inserted in one of the free pump outlets. It will cut current to the pump motor if the pressure is exceeded. You do not need a regulator, although Pumptec sells some if you want to experiment with one.

Performance
This design makes between 2.8 and 3.2 gph (Socal waters) at approx. 14A or about 4.5A/gallon. Water quality is 105-110 ppm. You do not need a feed pump (adds complexity). Best performance is around 850-900 psi. The pressure can vary somewhat with voltage (i.e. if you set the unit in operation at 12.2V and then the solar panels kick in raising the voltage to 14.4V, then the pressure will increase by about 100 psi. So, either you need to be careful when setting the max operating pressure, you need a safety switch or you need to tend to the watermaker. I typically run it when the engine is running to minimize the relative noise.

Improvements
I believe the water maker can be improved in a couple of ways. If we connect a longer membrane, say 2521, I believe the water output will increase to around 4 - 4.5 gph without losing much water quality (i.e. the ppm can jump to 200-250 ppm but that is still reasonable). One can add a soft start circuit to the motor, so that the needle valve can be left in its position and you only use an on/off switch to operate.

I believe this is the lowest cost watermaker on the market today, using standard parts (stainless steel pump, good pressure vessels, etc.). For the record, I experimented with cheaper stainless steel vessels rated for 300 psi and they work fine at 1,000 psi after strengthening the bolts, etc. but it is too much effort to save a few bucks. The pump motor combo is incredible, the pump is supposedly 96% efficient, the motor has average efficiency. It may be worth experimenting with a more efficient, higher output motor (the pump will just turn faster, allowing higher water output) but I never bothered.

Comparison to PS35 / PS40.
This unit makes double the water for one quarter of the price of the PS40. It is noisier but the noise is a regular pump noise vs. the thumping sound of the PS40 which some find objectionable. I have both on the boat and I use 3 gph watarmaker much more often.

Reliability
I have had the pump in various configurations for over a year. Max continuous run times has been about 18 hours. Never had any issues. I have had the watermaker sit unused for over two months, then it starts with no problems and the water quality is as described above. I see no need for regular cleanings, just run it every now and then to replenish the water.

Good luck and let me know if you have questions.

SV Pizzazz
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Old 26-10-2019, 14:16   #2
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Re: Small watermaker 3 gph

I am looking to build a watermaker and came across this thread. My plan was to go with a 1.6gpm hp pump driven by a 1hp 12v motor ( I have a 300ah lithium bank and a high output alternator) and a 2540 membrane but I am intrigued by your system. It certainly wins on cost and current draw. But isn't the recommended min flow on the membrane around 1.4 gpm?
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Old 26-10-2019, 15:44   #3
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Re: Small watermaker 3 gph

It depends on the membrane. It is suggested that the product to bribe ratio is 1:3 minimum (25% recovery but you can go to 30-35% recovery without losing too much ppm). Most small watermakers operate at 20-30% recovery, essentially trading membrane life for efficiency. Since membranes are $150 today, it is a good trade off. I am using the smallest membrane (14) which gives me a 1:4 ratio, and I think you will be OK with the next size up. The key cost driver is the pump/motor combo and this is the best I could find searching the web. Of course you can go to a 1 hp motor and above but the costs become significant ($500 for the motor, $900 for the pump) plus the current draw and noise become onerous. My design is driven by the pump/motor combo, it works well and is all stainless. The other way is to drive the design by the membrane (30 gph recommended for 21 and 90 gph recommended for 40). It really depends on what you are optimizing for, cost, simplicity, output, membrane life, etc.).
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Old 26-10-2019, 16:30   #4
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Re: Small watermaker 3 gph

Pizzazz,

Thanks for posting this. A DIY Watermaker is a very interesting topic.
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Old 26-10-2019, 18:10   #5
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Re: Small watermaker 3 gph

thanks for the reply, your design has given me some good food for thought, in addition to the low cost and low draw I really like the simplicity and of your design.
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Old 26-10-2019, 18:44   #6
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Re: Small watermaker 3 gph

Just FYI, I had a much more complicated design with solenoid switches for water intake and cleaning, a voltage regulator (instead of a pressure regulator) and so on and in the end decided that the complexity is not worth the cost. My guideline has always been the PS35, which only has one switch, on-off with nothing ever to adjust. This one gets close, you still need to adjust the pressure to suit different waters but the adjustments are minimal. The safety switch at 1,000 psi gives you a peace of mind, for example, I would switch it on, on a timer for 10 hours, then leave the boat to go to the islands. When I come back in the evening, the tank is full. But it does take some effort to make sure all the connections are air tight. For example, I was using an older filter housing with a degraded o-ring. The pump kept losing the pressure and I could not figure out why until I replaced that seal. It was a simple fix if you think about it but it took me some time .
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Old 26-10-2019, 19:27   #7
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Re: Small watermaker 3 gph

When you say water quality in relation to ppm, what is the ppm? Salt?
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Old 26-10-2019, 20:03   #8
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Re: Small watermaker 3 gph

Quote:
Originally Posted by Pizzazz View Post
I am sharing my 3 gph watermaker design for those who want to DIY. After many months of experimentation I settled on the following design:

Parts
- Pumptec 116C stainless steel pump/motor combo. Make sure you order the .105 CAM which gives you around 15 gph total flow. The cost is substantially less than $500, feel free to negotiate with distributors but I can't disclose the actual discount I am getting.
Have you found any other suitable pumps? Any other ways to obtain the pressure, even with lower efficiency if the cost is much lower?

I don't know much about the price of the pump but the electric motor itself should not cost much at this power level (15 amps). A brushless motor would cost $20 to $30 and have even higher efficiency than what you are using.

Quote:
Design
Salt water goes from intake to a strainer, 20-micron filter and then to the pump. The pump has three inlets and three outlets. Plug the four that you do not need. The pump output is attached directly to the pressure vessel (to minimize the number of connections). The high pressure output from the vessel goes (via a suitable length hose) to a t-connector that has a 1,500 psi gauge on one end and a needle valve on the other end. After the needle valve you can use common low pressure hose and fittings.
Could you post a schematic?
Quote:


Performance
This design makes between 2.8 and 3.2 gph (Socal waters) at approx. 14A or about 4.5A/gallon. Water quality is 105-110 ppm. You do not need a feed pump (adds complexity). Best performance is around 850-900 psi. The pressure can vary somewhat with voltage (i.e. if you set the unit in operation at 12.2V and then the solar panels kick in raising the voltage to 14.4V, then the pressure will
What about using a voltage regulator to supply 12.2 volts always? The supplies that can do this are very cheap and can also set a current limit in amps. Could this eliminate the need for pressure valves.
Quote:
increase by about 100 psi. So, either you need to be careful when setting the max operating pressure, you need a safety switch or you need to tend to the watermaker. I typically run it when the engine is running to minimize the relative noise.
Noise insulated box?
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Old 27-10-2019, 07:12   #9
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Re: Small watermaker 3 gph

The key to Pizzaz's design is the low cost hp pump. Stainless high pressure pumps that can do 800psi are ~1,000-1500 USD and up. Its the cheapest HP pump I have seen in my research for my DIY watermaker by a good margin and comes with the motor to drive it. The next cheapest option that is stainless and not brass that I have found is about 1,200 USD for motor and pump for a general pump wm series and a cheap Chinese 12v motor to drive it.
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Old 27-10-2019, 07:59   #10
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Re: Small watermaker 3 gph

Hi Pizzaz,

I used this pressure pump on my water maker, 40 inch x 2.5 inch,
Its a 240 volt motor I run off my 3000 watt invertor,
It puts out 3200 PSI but is regulated to run a constant 900 PSI thru my pressure gauge and valve before it goes into the Pressure vessel and Membrane,

Water inlet is thru a dedicated thru hull, then a course strainer and then 20 Micron filter into the pump,
Its Just a pressure washer similar to a karcher, But the Karcher was too big for where I wanted to install the motor,
I have only tested it on the watermaker using a water hose connection,
My boat is still on the hard,
Next week I will use sea water to test it out, My boat will be back in the water,
This particular pump sucks water up about 3 feet, Self priming,
I havent tried it above 3 feet,

Its an aluminium pump, But for $90-00 delivered, If it packs it in, I just buy another one,
The clip on fittings I have installed cost aprox $30-00, But I can also use it as a pressure washer to wash my boat just by clipping on the washer hose, Or as a fire hose in case of fire,

So far I have used the pressure pump for about 24 hours continuous, washing my boat, With no problems,

I did this to replace the 12 volt motor on my Little wonder water maker,
12 volt motor for my little wonder was $1100-00 plus delivery,

This Pressure gauge and valve were $30-00 the pair, Delivered, I bought them as spares,
I go this idea off Youtube where there was a DIY watermaker using the Karcher pressure washer as the pressure pump for the watermaker with off the shelf parts,

Thanks for your system too,

Cheers, Brian,
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Old 27-10-2019, 09:37   #11
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Re: Small watermaker 3 gph

Brian, aluminum pressure washer pumps do not work well with salt water. We have discussed this many times. Many people have experimented with these and they do work for a while but eventually they go bad. There is good design and bad design. Aluminum is just a bad design choice for a good water maker. It will work for a while, may be for a crossing but then you will have to replace it. So you will get tired of fiddling with it. You want a system that will work reliably one, two, five years down the road. This means stainless steel pumps and fiberglass vessels. On that note, I experimented with cheap stainless steel vessels, rated for 300 psi. Spoke to the manufacturer, they said the pins will bend at high pressure. So I replaced the pins with stainless steel bolts. It worked no problem and you could have a pressure vessel for $100 vs. $300. However, after a while the 304 steel starts rusting, the bolts get embedded into the tube, so it is difficult to replace the membrane and the savings were not worth it. So I went to fiberglass which works well.

The big issue with watermakers is that it is a low volume business and the parts are expensive. The key is to find good enough components from other, high volume industries (misting pumps, etc.) that are rated for corrosive liquids. The same can be said about pressure regulators. These things should cost $10 (it is a simple pressure relief valve) but it is difficult to find one for low flow applications.

If we want to try to improve on the design above we need to find the right components without sacrificing reliability and efficiency. A voltage regulator can help (you can regulate voltage in lieu of pressure) but you lose efficiency with those cheap regulators and you want to run the spec at max voltage anyway because it is a small pump. A pressure regulator could be ideal but I have not found a suitable pressure regulating valve (I found one for $600 which defeats the purpose). A great way to improve the design is to find a more powerful and more efficient motor but again these are expensive (you want a fully inclosed, 1/4 hp 12V motor with the right shaft and mounting holes, at least 70-75% efficient - if you find one for less than $400, please let us know).

What I like about my design above is that is has been running for years without issues. You need this on any boat systems. By the way, if you talk to pumptec, they will let you know that many people buy these pump/motor combos either for lab liquids or for watermakers. They are even thinking about building larger pumps to address the market.

Good luck and thank you for the comments.

SV Pizzazz
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Old 27-10-2019, 10:10   #12
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Re: Small watermaker 3 gph

Pizzazz--

Can you share the list of components in your finalized design? Pretty please?
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Old 27-10-2019, 10:14   #13
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Re: Small watermaker 3 gph

Good info - thanks
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Old 14-11-2019, 17:43   #14
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Re: Small watermaker 3 gph

I'm getting close to puling the trigger on parts for my own DIY watermaker. I'm either going with your design or a 1.6gpm general pump stainless HP coupled with a 1HP 12vdc drive motor feeding a 2.5x40 membrane and have another question about your system.


Is a feed pump not needed because of the design of the pumptec being tolerant of a possible run dry situation or does your design skip it as an acceptable risk due to the low cost of the pumptec?
thanks again!
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Old 14-11-2019, 17:50   #15
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Re: Small watermaker 3 gph

This is very interesting.

Could you please give me a ball park idea of the dimensions and weight of this rig?


Thanks!
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