Desalination Theory

How Desalination Works

Desalination sounds complex, but it’s really quite simple in practice.

The Rainman desalinator works by reverse osmosis, where high pressure is used to force water through a membrane, leaving pure water on one side, and salty water on the other.

It’s a bit like forcing water through a filter, except with reverse osmosis the pure water is forced through the membrane on a molecular level.

Sea water reverse osmosis takes a lot of pressure- about 800 PSI or 55 Bar. That’s about the pressure you’d find half a kilometre beneath the sea.

In the Rainman desalinator, a Honda engine or electric motor drives a Jabsco impeller pump and a General Pump high-pressure plunger pump. If the setup reminds you of a high-powered pressure washer, it’s because it is similar. Honda engines and General Pump Piston Pumps are the workhorses of the commercial pressure washing industry.

The impeller pump lifts the seawater, and the high pressure pump raises the pressure to around 800 PSI.

The high-pressure seawater is fed into a fiberglass pressure vessel that contains a Dow Filmtec reverse osmosis membrane.

The water flows past the outside of the membrane, which resembles a hollow plastic tube. In fact, the membrane is layer upon layer of thin films of plastic, which allow fresh water to permeate through to the inside of the tube.

Only a fraction of the high-pressure seawater is converted to pure drinking water. About 85 percent simply washes by the membrane and is flushed out the other end. It might seem wasteful, but the constant flowing of water past the membrane cleans it, preventing the membrane from clogging up.

To see how this theory applies to Rainman’s portable system, have a look at our¬†detailed schematic¬†diagram.