How Desalination Works
Understanding how desalination works helps one to realize that despite how complex it sounds, it really is quite simple.
The entire process of desalination is one of reverse osmosis. Basically water is forced through a membrane using high pressure. The result is fresh drinking water on one end and salty water on the other. This process is almost pushing water through a filter with the exception that reverse osmosis makes use of a molecular membrane.
In order to get the sea water out through reverse osmosis a lot of pressure is required, up to 800 PSI or 55 Bar. That level of pressure is usually what is found half a kilometre beneath the sea.
The Rainman desalination system makes use of a jabsco impeller pump as well as a General Pump high-pressure plunger pump which are both run by either a Honda engine or an electric motor. There is a marked similarity between this pump and a high-powered pressure washer and this is because most commercial pressure washing machines are powered by Honda engines and General Pump Piston Pumps.
There is a fiberglass pressure vessel which has a Dow Filmetec reverse osmosis membrane and it is into this that high-pressured seawater is channelled. In order to get the necessary 800 PSI or pressure, the impeller pump is used to lift the seawater to a certain level so that the high pressure pump can function.
On the outer part of the membrane is what looks like a hollow plastic tube and water flows through this. The membrane itself is more like several layers of thin films of plastic designed to let fresh water permeate inside the tube.
It is important to note that the amount of high-pressure seawater that is converted to pure drinking water is a small fraction as up to 85 percent flows past the membrane and gets flushed out at the other end. This continuous flow of water is necessary to prevent the membrane from clogging up.