You need to understand how the membranes work to see the difference.
High water pressure is used to force pure water through the membrane leaving the salt
behind, but the water left behind remains at high pressure,
and once made its way through the membrane is dumped overboard
, loosing all the energy used to create the high pressure.
Putting a second membrane in series takes the high pressure saltier water left from the first membrane and gives it a second chance to get through the second one before going overboard
. Well why not a third or fourth too?
Because it became saltier, the second chance is less productive.
In fact, you can take that 2nd chance water and run it through the same membrane twice and not pay for a second membrane, but that requires more complicated plumbing
The best setup is to take that high pressure water and use it to increase the pressure of the next batch of incoming low pressure water, the so-called energy-recovery pump watermaker
Putting a second membrane in parallel splits the flow between the two membranes at the same pressure, so the output is reduced, you need higher flow to get more production, but this uses more energy, really just like a second watermaker
running, but sharing a pump that works twice as hard,
so there is no energy savings, just more production.
Hope that helps.
Originally Posted by ericoh88
I got this boat last year. Managed to work on the 20gph water maker (Watermaker, Inc) last week. The set up is a 110v 3/4hp booster pump 4024 below water line with a 110v 1hp CAT pump with a cut out at 1025 psi with a single 40" membrane.
Ran the wm twice for 2 hours producing some 45 gallons with 205 ppm reading. Really cool.
I read from the specs from manufacturer website and others, that this 1hp CAT can drive 2 membrane giving additional 10 gph making this set up a 30gph.
I have seen from diagrams, some membrane are installed parallel while most are in series.
My question is which set up is better, in series or parallel?