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04 Marine · 21-09-2009, 11:57

Have you ever opened a bottle of pop? What happens to the compressed gases, they bubble right through the liquid and out the top. Same thing that will happen when you open a valve to let that water gas mixture out of the cylinder. The up side is that you will remove pollen and dust from the air as it moves through the membrane, might help your allergies and reduce the dusting requirement in the boat, but your air tank will quickly assume 0 PSI.

Now if you want to blaze that new technology, use the air pressure to drive a piston to pressurize the water. Now develop a system to release the pressure and one to return the piston to the starting position so that water can be injected in front of it again and then drive the piston forward once more. Sounds like we are building a steam locomotive. Can you imagine what that would sound like each time the air pressure was released. Perhaps it would be less objectionable to others in the anchorage if you used the air pressure to drive a music box wheel that could play sea shanties.

I build custom things out of metal and use argon gas to sheild the TIG welder. It starts with about 3,400 PSI in the cylinder which hold 55 cubic feet of gas. That cylinder is empty in about 6 hours of welding. Less if I use a higher flow rate. With 2,000 PSI trying to keep an 800 PSI system charged I suspect your time between refills would be minutes not hours.

If your handy with tools and wait for the right Ebay price you should be able to build a watermaker for around $1,000 to 1,200. admittedly, every major tool in my shop, plasma table, lathe and mill are CNC driven. I would like to think that I can keep my cost under $800 or 900 and be able to produce 5 or 6 GPH with a low draw on the 12VDC system.

I'm not trying to be mean, just to offer a pinch of reality.

sandinmytea · 21-09-2009, 15:02

I am not suggesting purging a bunch of air into the water, I was suggesting using the piston concept you just described. I am also not talking about purifying a ton of water.

A small air compressor compressing air into a small air tank. That air is forced into a small piston/cylinder arrangement containing raw (particulate filtered) seawater. That seawater is forced at high pressure through a small channel, and then through the R.O. membranes. Finally, it would empty l into a tank of (allegedly clean) water.

When you are releasing your welding gases, they are doing just that, venting into the air. What I am trying to describe is a (fairly) closed system that would use a compression chamber to force water. The pressure provided by the air cylinder could only be released by forcing the water through the appropriate filtration membranes. There wouldn't be any major release of air. When the raw water in the compression cylinder is exhausted, you would need a piston upstroke, as you described, but nothing fantastic. It could be done manually even, if nothing could be built to provide the return force.

We are not talking about 200gal/day or anything. The thread got started describing a guy's decision to try and cheat to find a way to get 2 or 3 gallons a day. I've thought about this quite a bit. I will give it a run once the opportunity presents itself. I am not trying to reinvent the wheel, nor sell my idea. Just thinking of cheap alternatives.

osirissail · 22-09-2009, 05:57

- - I also thought you were thinking of a tank with water in it and then pressurizing it to 800-820 psi by injecting air. As stated that would not work as the air would pass through the water then the membrane leaving the water behind.
- - Using a pump like the "Clark" pump that is in the "Spectra" water makers - an opposing dual cylinder piston pump - driven by air pressure if possibly do-able. But any piston system would have to add air to keep the pressure steady at 800-820 psi as the volume of the moving piston changes. Here you are using an intermediate motor to drive an aircompressor to drive the water piston pump. Why not just drive the water piston pump directly and cut out the "middle man?" The extra step means extra energy (electricity needed).
- - How about switching mediums and eliminating the electricity? Use steam generated by gas flame. The old steam locomotives worked quite well and it might be interesting to hear your boat go by making the chugga, chugga, whomp, whomp, hsss noise as you make R.O. water. And having a steam whistle would be neat.
- - The most practical way to power an R.O. system is your engine. A high pressure pump mounted directly on the engine with sufficient belts to transfer the power to the pump. Then h.p. hoses to the R.O. Membrane. All the parts necessary are available either new individually or you can purchase old parts from the scrap heaps of dead R.O. machines and put a system together.
- - Basic parts needed are 5 mic particulate filter; low pressure pump to suck the seawater through the filter and deliver it to the h.p. pump; R.O. membranes/container units; a h.p. regulator valve between the output of the R.O. membrane container and the brine discharge line along with a ball valve to bypass the regulator for cleaning.
- - For fresh water rinsing you need a charcoal filter and a valve to supply fresh water to the inlet of the 5 mic particulate filter.
- - Some of these parts are available at your local discount home store and the others off the internet or boat junk stores (stores selling discarded and old parts from boats).

seandepagnier · 22-09-2009, 10:40

Quote:

Originally Posted by osirissail

- - I also thought you were thinking of a tank with water in it and then pressurizing it to 800-820 psi by injecting air. As stated that would not work as the air would pass through the water then the membrane leaving the water behind.

That is actually not true. If gravity keeps the water in place, the air will not be in contact with the membrane (try not to do a 360 when making water)

- - Using a pump like the "Clark" pump that is in the "Spectra" water makers - an opposing dual cylinder piston pump - driven by air pressure if possibly do-able. But any piston system would have to add air to keep the pressure steady at 800-820 psi as the volume of the moving piston changes. Here you are using an intermediate motor to drive an aircompressor to drive the water piston pump. Why not just drive the water piston pump directly and cut out the "middle man?" The extra step means extra energy (electricity needed).
- - How about switching mediums and eliminating the electricity? Use steam generated by gas flame. The old steam locomotives worked quite well and it might be interesting to hear your boat go by making the chugga, chugga, whomp, whomp, hsss noise as you make R.O. water. And having a steam whistle would be neat.
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Or run it on drift wood. Then it heats your boat too.
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