How do they work????

How do they work????

Most marine watermakers use a process known as reverse osmosis to extract fresh water from brine. Basically it involves putting the sea water under pressure (some 800 - 900psi) over a semi permeable coiled membrane. Fresh water then migrates through the membrane and is collected, leaving a more concentrated brine solution behind. As only about 10% of the brine passed over the membrane passes through, the remaining 90% is dumped overboard. There are basically two ways to achieve the pressure needed for reverse osmosis to take place. Traditionally a high pressure piston 'cat' type pump is used, this has the advantage of being slightly less expensive than other methods but on the downside these type of pumps use a lot of power, are noisy, require regular maintenance and will unfortunately die if run dry. Modern technological advances have seen the evolution of the energy recovery pump. This is a unit driven by a small dc feed pump which amplifies the pressure to the required level using a combination of Valves and pistons. Energy recovery units are very efficient, quiet in operation and need little maintenance. The diaphragm pumps used are self priming and suffer no ill effects if run dry. On the down side energy recovery systems tend to be more expensive.