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OP-4 FRESH WATER FLUSH
The purpose of the fresh water flush is to replace the sea water in the watermaker with fresh
water whenever the system is not operating. The “Auto Flush Mode” on the MPC 3000
changes the fresh water every five days if the system has been idle that long. The watermaker
will last longer and operate better if it is always kept filled with fresh water between uses.
Most spectra watermakers are equipped with a fresh water flush module. This module in-
cludes a 50 micron filter to filter out abrasive particles in the feed water that might damage the
feed pump, a charcoal filter to remove any chlorine in the fresh water that might damage the
membrane, an electrically operated valve and a check, or “one way”, valve. The electrically
operated solenoid valve opens during the fresh water flush allowing the boats pressurized wa-
ter system to supply water to the system. The check valve prevents the fresh water from going
out backwards through the sea strainer and sea cock. The charcoal filter has a maximum flow
rate of 1.5 gallons per minute (6lpm) so the feed pump is operated at a reduced speed on some
models, or is cycled on and off on other models, to avoid exceeding this flow rate.
If the ship’s water system is unable to provide flush water at the required flow rate, sea water
will be drawn in to make up the difference. This will cause the flush water to be brackish, and
ineffective in preserving the watermaker. At initial startup the fresh water flush system should
be tested by taking a sample of the brine discharge water just as the flush cycle is ending.
This water should not taste salty, and should read less than 1000 ppm on a digital tds meter.
The flush cycle can also be tested by closing the sea cock during the flush cycle. If the MPC-
5000 display gives a CK SEA STRAINER alarm this means that the fresh water supply is in-
sufficient.
Because the pre-filters trap the plankton in the feed water they can be subject to “going an-
aerobic” or starting to smell like rotten eggs, as the trapped plankton decay. For this reason it
is advisable to always put in clean elements if the unit is going to be left on Auto Flush Mode.
In daily or regular use the fresh water flush after each shutdown will help prevent this prob-
lem, but in excessively warm or fertile waters the pre-filters will need regular attention.
7/26/04
