Originally Posted by 44'cruisingcat
Thanks for the detailed answer Tellie. I'm not sure I worded the question very well.
Let's say I have a 60LPH watermaker
, with a 10:1 bypass ratio. So the pump delivers 660LPH at 800 psi.
I'm wondering if I changed the membrane to one rated at 120LPH at 800psi, but ran it at a lower pressure, so it was still only producing 60LPH of product, so it would still be running at a 10:1 bypass ratio, because the pump is still delivering 660LPH, but at maybe 650-700psi. (the bypass ratio might possibly be slightly more, since the pump tends to run a little faster at lower pressure.)
But by running at the lower pressure it might use a little less power. (I've observed this - at lower pressure the pump does run faster and draws less amps.)
Seawater at 36,000 PPM typically has an osmotic pressure of about 376 PSI (26.75 Bar). At 800psi from the pump the differential pressure would be 800- 376=424psi.
This is the actual pressure which forces the water
to move through the membrane.
If you lower the pressure to 650 psi the diff. pressure would be only 274 psi. If we assume linear relation, you will lower the water
production by 35%