I am not sure either of you guys has any idea what goes on inside a R/O
pressure vessel. First of all the normal pressure range for a seawater
system is between 750 and 850PSI. Seawater R/O membranes are made from
completely different materials and construction from municipal and most
other industrial purification membranes. They can withstand pressures
almost twice that high. Unless they are damaged by chlorine they don't
leak. The only O-ring that might potentially leak brine into the product is
at the output end of the product tube. Any leakage there would immediately
raise the salt level above the drinkable level. The other two O-rings seal
the pressure vessel itself and when they start to leak with 800PSI behind
them the result is more than a little bit noticeable.

Now as to squashed bacteria. The process of reverse osmosis is not simply
squeezing water through super small holes. The salt is rejected by the
electrical charge of the salt ions. The charged ions are pushed away from
the membrane surface. In the process bacterial is pushed away with the
ions. The seawater flow across the membrane surface is 7 times that of the
product flowing through it. Bacteria being several million times larger
than the salt ions are swept away so they never get a chance to collect on
the membrane in normal operation. If you leave the membrane idle for
several days however the bacteria can settle on the membrane and start
reproducing and THAT can cause clogging. What causes scaling is the
accumulation of molecules of minerals with very low charge. A flush with a
mild acid every couple of hundred operating hours will take care of that.

Normally R/O desalinated water is 100% free of bacteria but if you are
drawing from a harbor or other polluted water with a high virus count
statistically some viruses can get through the membrane and that is what UV
post treatment is for.

--
Glenn Ashmore

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