Water maker comps

[GRNordstrom]

For "a64pilot": Who is Tellie and how do I call him?
Thanks,
Ray

[ronstory]

see Post #134 for Tellie

[Tellie]

Originally Posted by GRNordstrom

For "a64pilot": Who is Tellie and how do I call him?
Thanks,
Ray

I don't who he is anymore and my wife has thrown her hands up in the air and given up on him too. Please don't call him what she does. But try this number anyway. (954) 515-7077

[Pizzazz]

I came across an interesting pump that can be used for seawater desalination and I am trying to figure out if it is worth experimenting with to build a lower cost watermaker.

The pump/motor combo is stainless steel, ceramic plungers, optimized for seawater. It is 94% efficient (the vendor states highest efficiency pump on the market). It is a small pump though, producing 0.25 gpm @ 800 psi @ 14A @ 12V. I believe it is a 1/6 hp motor. The set can be had for around $450 I believe.

Should I use a 2.5 x 21" or 2.5 x 40" membrane with it? I also learned (in this forum) that the recovery rate will increase with decreasing flow up to a point and then once the increased osmotic pressure of the concentrate approaches 800 psi, the salinity of the product water will increase dramatically. The question is, what is that recovery rate limit?

Dow states that membranes perform optimally at 5-8% recovery and the max recommended recovery is 15%. They also state that in small applications, such as those on a sailboat, many vendors run the systems at recovery rates of 30-35% and this is OK, although it shortens the life of the membrane by a bit. Some research papers state that the max recovery for cross-flow membrane systems is around 45%.

The simpler way to ask the question is, do you believe that running 0.25 gpm through a 2.5 x 40" membrane will increase the salinity of the product water too much to make it unusable?

Further, if operating close to the limit may be efficient, the system may be sensitive to the temperature, salinity, etc. I want to avoid a situation where the watermaker makes 4-5 gph in warm waters but it goes over the limit in cold waters so it becomes unusable. So, there has to be a margin of error built in.

If all works out, though, I believe it would be possible to put together a nice, 4-5 gph watermaker system with a stainless steel pump, reasonably efficient at around 2-3 amps/gallon for less than $1,000. Brand new.

Thank you,
SV Pizzazz

[Tellie]

.25gpm is way to low a flow. If the pump is $450 how are you going to put the rest of it together for less than $550?

[Pizzazz]

Tellie,

$450 is for the pump, motor and safety valve combo. It a positive displacement pump, so not need for a feed pump at all. It just has to be flooded or below the waterline. You know the rest of the prices better than me.

On the flow rate, .25 gpm is low but this is the best value pump I could find. It depends on the membrane, right? We know that 0.5 gpm works on the 21" membrane with approx. 20-25% recovery. So, the 14" membrane, which has half the surface area should work, giving 3 gpm. The question is if we can get 5 gpm with a longer membrane. The 40" likely would not work, the 21" - may be.

A related question, one of the vendors claimed that it was not salt water per se that was damaging to the pumps but dry salt on the surface that when exposed to air starts eating away the metal. It made sense to me but I am not sure if that is totally correct. He claimed that you could use a brass pump just as well as stainless as long as you always keep the brass pump submerged (even flushing with fresh water would not remove all the salt). Does this sound plausible to you?

SV Pizzazz

[Fuss]

Originally Posted by Pizzazz

Tellie,

$450 is for the pump, motor and safety valve combo. It a positive displacement pump, so not need for a feed pump at all. It just has to be flooded or below the waterline. You know the rest of the prices better than me.

On the flow rate, .25 gpm is low but this is the best value pump I could find. It depends on the membrane, right? We know that 0.5 gpm works on the 21" membrane with approx. 20-25% recovery. So, the 14" membrane, which has half the surface area should work, giving 3 gpm. The question is if we can get 5 gpm with a longer membrane. The 40" likely would not work, the 21" - may be.

A related question, one of the vendors claimed that it was not salt water per se that was damaging to the pumps but dry salt on the surface that when exposed to air starts eating away the metal. It made sense to me but I am not sure if that is totally correct. He claimed that you could use a brass pump just as well as stainless as long as you always keep the brass pump submerged (even flushing with fresh water would not remove all the salt). Does this sound plausible to you?

SV Pizzazz

While I admire being inventive and I like doing these things myself, you have to really know what you are doing when reinventing the wheel, else over time you will end up with either, something that doesn't work properly or something that works properly but ended up costing more than if the correct parts had been bought in the first place. Sort of pay me now or pay me later.
I think building a watermaker is an interesting project, but I would recommend using tested parts and knowing what production rate you want to achieve. So buying the correct membranes and pump to suit is important, the rest you can experiment with, there is more than enough other parts required that you can be inventive with.

[Tellie]

Yeah, I'd find another vendor. Brass will work, for a very short period. Just like galvanized nuts and bolts on a boat will work, afor a very short period. No one in the industry would use brass on anything, no one reputable that is. I think Fuss above has given a great response also. I never started out wanting to be in the watermaker business, man I was retired back then. I started out when the wife stated she wouln't step back on board if I didn't get a watermaker. I looked at the prices and like so many others said I could build my own cheaper. I built many watermakers after my first one. It took me three tries to get it right for my own boat. By the time I was done (and valued my time at minimum wage) I could have bought any commercial watermaker, had money left over, and saved a whole lot of time that could have been better spent sailing. One of my weaknesses is that I tend to take on "distracting projects". If you could make a decent 3gph watermaker for anywhere near 1K I'd triple the price and still beat the begeeebers out of the small watermaker companies, and I would have been rich by now. I applaud your desire and willingness to research this and I would never discourage you. But if you can do this, let me be the first to know. I assure you with your system and my contacts we'll both be looking at bigger boats within two years, and selling the company for millions in four years. I would suggest that what you are really looking for is something like Rich Boren offers with his Cruise RO systems or a Rainman which we offer.