Optimizing Freshwater Flush - Vane Pump Systems


Note: Vane Pump systems include Catalina & Newport Models


Optimizing the Fresh Water Flush Duration Overview:

5 minutes or so is usually the right flush duration to ensure that sea water is thoroughly flushed out of the watermaker using the least amount of fresh water. However, due to different lengths of hose runs, different rates of flow, and different pressures in shipboard fresh water systems, the flush duration can be optimized for your boat; Your system may require more than 5 minutes to adequately flush the system, or you might need less time, allowing you to save more fresh water. However, you must ensure the system is adequately flushed. Do not try to save a gallon of water at the expense of your system longevity, run your watermaker for a few more minutes to make up the difference.

Optimize the time:

Ideally the salinity of the brine discharge will be completely fresh just as the flush cycle is completed. Using the brine discharge service hose, direct the brine discharge into a bucket. While the system is freshwater flushing, take repeated samples from the brine discharge and test it with a handheld salinity meter. When the PPM drops below 1000 you can consider the system to have been fresh water flushed and note the elapsed time. This will be your optimum flush duration going forward.


If the water is salty, then you must increase your flush duration to the appropriate time necessary to get all the salt out of the system. Many people will start the test over and take various samples to dial in the exact time necessary.

If you continue to have salt in your flush water, you are most likely drawing seawater in during the flush. This is because the Spectra vane pump and the ship's freshwater pump speeds do not match. One way to confirm this is to close your thru-hull and perform a freshwater flush. You might see/hear air being drawn into the filter bowls, a cavitating feed pump, or even a prefilter fault alarm. The remedy for this is to slow down the pump flush/service speed (for DC systems this procedure is described here Slowing Down Vane Pump During FWF).

Once you change your flush speed, you should make water for a few minutes and again check the ppm of the discharge with the thru-hull open to be sure the flush duration does not need to be extended.