Some thoughts on feed flow, Hp pump vibrations and flow. Im not sure how in-tune you are with your watermaker, but i keep an eye on the pressure gauge placed between micron filters and HP pump inlet. If feed pump cuts off I hear and observe immediate difference and shut the watermaker down before serious damage (manifold cracks due to vibrations or fiberglass
vessel endcap fails due to pressure spikes). I have observed better brine flow(lower vibration) performance with higher PSI at the inlet of HP pump. I've tried anywhere from small vacuum to 45 PSI. HP pump specs will show recommended inlet PSI. Usually in the range of small vacuum to 60PSI.
I am currently using flojet 4125 series. these pups are heavy duty and have integral overheat/over-current protection that will cut off if they run too hot. Prior to this I was given for free a flojet 4325 which was an overkill. I have an engine
driven cat 290 (2.5gal/min) with 2 filmtec 2540 membranes in parallel. Few things i learned from this feed pump:
If feed pump is too powerful it will run too hot, with plenty of inlet pressure, but protection will cut power off, and you might have to wait for pump to cool off. If there is no protection pump could get damaged. Look for words like continuous duty to ensure pump can run for long times. In my case I tried cooling
the pump but never got the fan and cooling
What worked better is adding a Tee with a valve after the feed pump so i could lower and adjust feed pump pressure. Keeping 5-10 PSI prevented the 4325 from further overheating
and diverted large portion of the feed water overboard
prior to micron filters.
After converting to lower flow pump (flojet 4125), I kept the bypass and I have had two seasons of use with anywhere from 5PSI to 30PSI of inlet pressure and 4125 never overheating
. I have not tried increasing the inlet pressure(shutting the bypass) due to prior experience of overheating. 4125 feels noticeably cooler to the touch. Ive been meaning to add a fan so i can increase the inlet PSI possibly eliminating the bypass, but have not gotten around to it. Also i have a rather large WM inlet . Its an 1.5" with scoop strainer. it was the old engine
intake so I just kept it instead of reducing. What i've learned is that sometimes I get significant vibrations on the high pressure side. Root cause was inadequate inlet flow(could be clogged filter, sometimes bioluminescents and other crap in harbors, or just maxed out inlet flow given the brine flow/pressure settings). As a result of using such a large inlet, I get much better performance if boat is moving forward while making water. It allows me to improve brine flow by rising engine RPMs and still avoid vibrations. While at anchor
same Brine flow/engine RPMs would result in much higher vibrations. So i just got used to making water while under way. It keeps me away from debris-filled harbors, and allows me to keep brine flow higher which helps with membrane clogging and growth accumulation.