Small watermaker 3 gph

[Pizzazz]

All membranes are more or less the same. In a small watermaker design you run the membrane at a much higher recovery rate than publishes. This reduces your power requirements, decreases the quality of the product water and shortens the life of the membrane. But it is a good trade off. I was told by Dow to aim at recovery rate of 1/3. This means that if the pump can push 15 gph through the membrane, I should aim for 5 gph product water and 10 gph brine. With the 14” membrane I am getting 3 gph (I think the pump is making a little less than 15 gph too, it depends on the battery voltage) @ 110 ppm fresh water quality. If I used the longer, 21” membrane, I expect around 4.5-5.0 gph but the product water quality will likely decrease to 200-300 ppm or higher. Without getting into too many details, there is a trade off between pump power, flow, membrane surface (length), quality of product water and membrane life (how quickly it will become congested).

In our case, we have selected the pump motor combo and it makes around 1/5 hp. This gives you a certain flow, that also depends on the dialed pressure.

The 14” membrane gives a little less than 3 gph at 110 ppm in my case. I was told to expect membrane lifetime of 2-3 years, have had no issues so far. This is a recovery rate of around 20-25% last time I calculated it.

If you use the 21” membrane, I expect around 4.5 gph and product quality around 300 ppm but I have not tested it.

If you use the 40” membrane, I think the membrane will foul up after a few minutes because 15 gph is a very low flow for the large membrane. It will be a waste.

As I have mentioned, I am happy with the 2.8-3.0 gph I make, and I stopped experimenting. Also, you can always increase the flow by raising the voltage (ie operating the watermaker at 14.4V, I think at some point I had connected three golf cart batteries in series to go to 19V and the motor took it well but it may burn faster this way). If someone tests the pump with the 21” membrane, please let us know.

One design choice that becomes apparent here is that you can increase the efficiency of the watermaker by increasing the recovery rate, allowing ppm to increase as well. It is not linear and after a certain point it jumps exponentially. However, you could probably make 5-6 gph at 500 ppm which is acceptable if you use the water for dishes, cooking (add less salt), etc. and not drinking.

Most of the commercial watermakers try to avoid liabilities and aim for higher quality water than what you need (temperature, initial salinity, membrane age, etc. all affect ppm), so if you are using this commercially, you want to have enough headroom to cover variability in those factors.

Lastly, the membranes that you buy from Dow have +/- 20% variability as well. It is not a precise science.

Bottom line, you can pair this pump either with 14” membrane to give you 3 gph (best case) @ 110 ppm or a 21” membrane to give you close to 5 gph at higher ppm. I chose the first option.

SV Pizzazz

[RaymondR]

That is a beautiful design Pizzazz.

[BjarneK]

Thank you very much for the detailed explanation. I get it now. It is amazing how many different things there are to learn as a sailor.

[Pizzazz]

If you want to get even more technical about the design and why I think this Pumptec pump is amazing for our needs, read the following.

Let's say we had unlimited resources and wanted to design a watermaker from scratch. We would chose a motor, pump, flow and membrane that provide a good flow, a good recovery rate and long life for the membrane. There will be enough headroom in the motor specs and the flow specs to guarantee years of reliable performance under different salinity, temperature and membrane variability. The cost will be a few thousand dollars, then we add support and profit and we end up with a $5,000 water maker and a market limited to offshore sailors (less than 8,000 globally, most of them already have one).

The other solution presented here is to take an existing high volume application (a misting stainless steel pump) and design around it. The Pumptec 116C pump makes 10.5 gph @ 800 psi with the .075 cam. We put on the biggest cam recommended by the manufacturer (.105) to get close to 15 gph. By doing so, we are stressing out the cheap motor, drawing higher amps. Is it more likely to burn out? May be but this is why it is so cheap. Then we optimize the membrane surface for the highest recovery rate (hence my suggestion to try it with both the 14" and the 21" membrane). With the longer membrane we are sacrificing long-term membrane life for better efficiency and accepting a lower product quality water. So, basically we have a design that uses off the shelf components and stresses each parameter as much as reasonable. This way we get a 3 to 5 gph watermaker for less than $1,000 that produces fresh water at 3 to 4.5 AHrs per gallon which is nearly twice as good as commercial alternatives (excluding Spectra which is an energy recovery watermaker). We accept that we will be replacing membranes more often (once every two years) because the cost of new membranes is ridiculously low (you will spend more on pre-filters than on membranes).

That is all there is to it. It would be difficult to sell commercially but for DIY I think it is close to perfect.

SV Pizzazz

[RaymondR]

And all that is why I feel you have created a beautiful design.

Spectra have a pump with energy recovery at the cost of considerable complexity and the baggage which always accompanies it - not just in the fabrication but also in the ongoing maintenance.

Provided one has the real estate to mount them, with the low cost of panels now, it is probably more economically efficient to expand the power supply than to recover the energy dissipated in the throttling device.

[jimbojonesbos]

Originally Posted by Pizzazz

As I have mentioned, I am happy with the 2.8-3.0 gph I make, and I stopped experimenting. Also, you can always increase the flow by raising the voltage (ie operating the watermaker at 14.4V, I think at some point I had connected three golf cart batteries in series to go to 19V and the motor took it well but it may burn faster this way).

I will be running mine at ~14v because I have a battleborn lithium bank. I am leaning toward not launching this year due to the pandemic so I likely won't be able to report back on experience with this pump at the higher voltage until 2021.

[Anders]

Very interesting design but how noisy is the pump?

[Capdave360]

Originally Posted by RaymondR

And all that is why I feel you have created a beautiful design.

Spectra have a pump with energy recovery at the cost of considerable complexity and the baggage which always accompanies it - not just in the fabrication but also in the ongoing maintenance.

Provided one has the real estate to mount them, with the low cost of panels now, it is probably more economically efficient to expand the power supply than to recover the energy dissipated in the throttling device.

So - real world, working today on anchor in Grenada - specs on a Spectra Cape Horn Extreme: Making 16 gph @ 9.5amps X 27V straight from the solar panels. So that's about 16W/gallon. The system first described here was 4.5amps/gal @ nominal 12.2V is 55W gal - That's a really really big difference.

We actually use about 15 gals/day with showers and dive gear rinsing and fresh water heads and galley and etc. Putting that back in one hour at 2pm with the batteries already at full charge and the solar panels putting out 600+W is easy....

The problem with low output watermakers is you have to run them for so long, and listen to them for so long. And at 55W/gal it becomes impractical.

So I put up with the complexity of the Spectra - which is essentially all in the Clarke pump; I carry a rebuilt spare. The rest of the system is OTS stuff. There's not really any additional maintenance - there's no maintenance items on the Clarke pump.

[Pizzazz]

Originally Posted by Capdave360

The problem with low output watermakers is you have to run them for so long, and listen to them for so long. And at 55W/gal it becomes impractical.

This is a very valid point. If you are cruising often, you either get a Spectra if running a DC boat or a high output AC watermaker if you have a generator. We settled this a while ago.

The problem with the Spectra is the high initial capital cost. Few boaters on smaller, less valuable boats will spend $5-6,000 on a watermaker, especially if they cruise part time. May be a different market than the readers of this forum, who seem to be hard core cruisers but the majority of the sailors around me like to go around the islands for one week at a time, then go back to work. For them, spending five six grand to be able to have unlimited water supply for a few weeks of the year is just not reasonable. But they do complain that the major limiting factor is that they run out of fresh water.

The idea of the small watermaker was to mimic the performance of the fridge. It costs around $1,500 to install a marine fridge, it takes around 60 AHrs per day to run and most boats have one. Cold beer I guess. The idea is to spend $1,500 for a watermaker, accept 60 AHrs a day electricity cost and have 15 gallons of fresh water per day which is about right for a couple. Unfortunately, it is noisier than a fridge and there is not much I can do about it right now. If you run it while sailing or motoring you don’t notice it but at a quiet anchorage/mooring, it is quite noticeable (to put it nicely).

On the power consumption side, imagine someone offered an energy recovery fridge that cost $6,000 but consumed 15 AHrs per day vs. 60 AHrs. Some will invest in it but most will just say, it is too much for a cold beer. The question then is why you value a fridge more than fresh water?

Also, if it breaks down (the pump or the membrane), the cost to fix is minor vs. the cost to fix a Spectra.

I agree though that if I were cruising for more than a few months every year I would probably invest in Spectra.

One additional thought I have had as a result of these discussions is if it makes sense to have the option to produce high quality and low quality water water through a combination of pump voltage or membrane length. It is a waste to use 100 ppm water for deck washing or even dish washing. Low quality water (500 ppm will do fine. Many of us drink bottled water, so technically one could set the water maker to high quality and refill the 2.5 gallon containers I use for drinking water, then set to low quality to refill the main tank and use that for everything else. Not sure it is worth the hassle but logically it makes sense.

SV Pizzazz

[RaymondR]

Precisely the point I was attempting to make.

The combination of the Pazzazz watermaker and the panels to run it is far cheaper from a capital expenditure viewpoint than the Spectra whilst the Spectra is considerably more efficient from a power consumption viewpoint.

However, once installed the sun light is effectively free and since it shines for say eight hours per day you just let the little Pizzazz run all day.

The Pizzazz is has considerably less space requirements also making it easier to locate in a boat.

Low cost for the economy cruiser, easily fabricated by the DIYer, small and easy to locate, simple to maintain and operate. Inherently safe (The motor will just stall and blow the fuse if you shut off the pressure bleed valve) It's an exceptionally good design and Pizzazz is to be congratulated for having devised it.

[Capdave360]

Originally Posted by RaymondR

However, once installed the sun light is effectively free and since it shines for say eight hours per day you just let the little Pizzazz run all day.

Not everything is about money. I don't know if you've ever actually operated such a high pressure pump, but believe me, you'll be dying to turn it off after an hour or two. Running it all day - maybe if you're not onboard??

Pizzazz talked about extending the water range of a 1-2 week cruise twice/year without investing in an expensive watermaker. His device might fulfill that mission, though I wonder about the Total Cost of Ownership over five years with budget components perhaps needing replacement.

And of course there's the electricity infrastructure - getting an additional 60AH/day out of solar panels/alternator/batteries on a small boat is not cheap either unless you already have it to spare.

I understand the desire to have it all on a tight budget, but in the end you can have good, fast, or cheap - pick any two.

[Pizzazz]

Originally Posted by RaymondR

The motor will just stall and blow the fuse if you shut off the pressure bleed valve) It's an exceptionally good design and Pizzazz is to be congratulated for having devised it.

Raymond, thanks for the kind words, no need for exaggerating my role, I just happened upon a good misting pump. One clarification, though, it is a positive displacement pump, so it will keep adding pressure until something breaks or the motor stalls. Pumptec told me to expect max pressure around 1,700-2,000 psi. Typically, the fiberglass vessels we use have 1,000 psi nominal rating, 6,000 psi test rating. The high pressure hose is 3-4,000 psi. Thus, most likely the motor will stall or a fitting will give (no big deal as it is a liquid, not a gas, so it will not explode and it is unlikely it will sink the boat for a couple of days.

Nevertheless, in order to save the membrane I would suggest a 15A fuse (limiting power to 180W) and/or a mechanical pressure switch or bleed valve at 1,000 psi. Last thing I want to do is encourage someone to sink her boat.

SV Pizzazz

[seandepagnier]

Originally Posted by Pizzazz

here is not much I can do about it right now. If you run it while sailing or motoring you don’t notice it but at a quiet anchorage/mooring, it is quite noticeable (to put it nicely).

Would it be possible to put it in a sound proof box? I have seen it done with engines.

What would you recommend if I would rather make only 1 gallon per hour and be as cheap as possible, but 15 amps is fine (plenty of solar)

I did just get an evacuuated tube for about $100. It is great for cooking as I have used it every day for more than a week even with clouds it cooks (takes much longer) it can also evaporate more than a gallon of water a day which puts it on similar price point as homemade watermakers.

[Pizzazz]

In designing an RO watermaker, we are bound by available membranes and the need to make 800+ psi pressure. The lowest output watermaker is the Powersurvivor 35 which makes 1.2 gph using around 4.5A per hour. It drives a large piston back and forth slowly. The operation is very quiet but at every cycle (once a second), there is a large thumping sound when max pressure is reached and the valve releases. It can drive you crazy. If the design can be modified to remove this noise, that would be a good silent water maker. It uses 12x1.8” membranes that HCTI makes for around $170 (half the OEM price).

There is also a 06 manual watermaker that makes 0.25 gph, may be it can be modified to take an external pump but the membranes would be hard to find.

All the other pumps use metal valves that produce a fairly significant chatter. You can definitely enclose the pump (it gets cooled down by the sea water anyway but I doubt you would make it as silent as a fridge. I will produce a short video shortly so that you can judge for yourself.

In terms of other technologies (flash evaporation, using engine hot water, etc.), the last time I looked at it, they were at least 3x-5x less efficient than RO. Fun to look at but a pain.

[RaymondR]

"Not everything is about money. I don't know if you've ever actually operated such a high pressure pump, but believe me, you'll be dying to turn it off after an hour or two. Running it all day - maybe if you're not onboard??"

You're waving a red rag at a rogue bull mate. I used to be an oil driller. The average offshore rig has at least two couple of thousand horsepower, positive displacement, pumps pressure rated to about 6,000 psi, so yes, I have operated a high pressure pump.

Then when one participates in the notorious "fracking" on deep, high pressure wells one uses a dozen or more smaller high pressure pumps to power "intensifiers" (Basically what your Spectra pump is) to boost the pressure up to 15,000 - 20,000 psi. You don't know noisy until you wander past all those GM 871 diesels going flat out.

The cleverness of Pizzazzs watermaker is it's extreme simplicity and use of low cost, off the shelf components. It's the balance of all factors economic and functional which makes it a good design.

The "doer and "haver" dichotomy.

Some of us don't have a lot of money to spend, some of us are just cheap buggers, some of us like to build stuff and some of us just like to dream ie doing. Then some of us just like spending money ie having.

There's a bit in there for everyone.