Marine Reverse Osmosis Systems
by Craig NortonCommercially, the reverse osmosis system has been in use since the early 70’s and although technological advancements have made systems smaller and more reliable since then, it is still the number one cause for headache onboard charter yachts. Problems arise particularly due to the continuous loads of heavy water demands and mostly because of inadequate service and maintenance. The theory of ’don’t fix it if it isn’t broken’ is usually the cause of your water maker breaking down.
Common problems can be avoided with a simple knowledge of how your reverse osmosis system works and what you can do to extend the life of all its components.
The feed water with which you pass through your system is most important to the lifespan of your pre-filters and membranes. Avoid running the water maker in heavily polluted anchorages or marinas, heavily silted waters and especially water with any fuel or oil present. The primary sediment strainer should be cleaned often and regular replacement of pre-filters will reduce loads forced on the pump.
The high pressure pump is the most expensive mechanical component of any system and should be cared for as such. Commonly used Cat pumps and a number of other brands require a lubricant to be added to the top of its valves and this should be added to your regular routine maintenance before every charter week or once a month under light load. Other maintenance to the pump could include making sure the belts are aligned and properly tensioned to avoid undue stress on the bearings.
Leaks are most likely to occur after the pump along the high pressure lines as these are under the most stress. Any salt buildup or beginnings of corrosion should be tended to and cleaned immediately. Slight corrosion in fittings and joins will soon become a drip and quickly compromise your system. Ensuring these high pressure lines are secured to something solid will reduce high pressure vibration which works SS fittings loose over time. When a fitting first shows signs of leaking, remove and clean the salt and rust deposits and refit with a little silicone. (Always use two wrenches when working with high pressure fittings).
The membranes of a reverse osmosis system are the single most expensive consumable item. It is therefore vital that the aforementioned pre-filters are changed frequently to maintain the health of the membranes. Water lying dormant within the membranes is equally as damaging as pollutants passing through. For this reason it is essential that your water maker be run as often as possible. Running the system at two thirds of its capacity reduces wear and can allow for more frequent uses when power consumption is not an issue.
When the raw water is of questionable quality the system can still be run by feeding fresh product water from your tanks to the intake of the system which is a great method to keep water flowing across the membranes while in the marina. This fresh water flush is also beneficial as it allows more time between operations without the water becoming stagnant. If you plan to leave the boat without the system being run for more than 5 days then pickling the membranes is highly recommended. When water consumption is low and you find yourself running the system just to keep it operational, you will find it better to run for 3 hours every three days than one hour per day.
Having worked as First Mate/ Engineer aboard the same charter yacht for 5 years I have been able to maintain a reverse osmosis system and avoid a costly membrane replacement or other serious defect by using these simple rules in my routine maintenance and service.