Small watermaker 3 gph

[Pizzazz]

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