SALT DIFFUSION
23
Rev C
Figure 15 Option 3 with Pressurized Tank
SALT DIFFUSION
Like all reverse osmosis systems, the Merlin uses semi-permeable
membrane elements to filter contaminants. When pressurized, this
membrane element allows water with low salt concentrations to pass
through, leaving higher concentrations of salt on the opposite side of the
element. Unpressurized, naturally occurring diffusion takes place between
the low salt permeate water and higher salt concentrate water. This
process, which happens in all RO systems when not in operation, begins to
equalize salt concentrations on each side of the element. After periods of
inactivity, measured TDS rejection of the permeate water held within the
RO membrane elements and manifold will have dropped below steady-
state rejection levels.
Salt Diffusion in Traditional RO Systems
In a typical home RO system, the salt-diffused permeate water created
through periods of inactivity is mixed into the storage tank. Over time, the
salt concentration within the storage tank slightly increases. The end
users are eventually forced to use salt-diffused water. This is one reason
why most RO manufacturers recommend flushing holding tanks on a
weekly basis — it minimizes, but does not eliminate, salt diffusion effects.
Salt Diffusion in the Merlin
After extended periods of inactivity in the Merlin system, any salt-diffused
water will be exhausted through the faucet when the system is operated.
After this water is flushed from the system, the RO continues producing
water at typical steady-state high rejection levels. The Merlin, therefore,
allows users to eliminate the effects of salt diffusion by simply running
their system for 1 to 4 minutes after extended periods of inactivity. For
most end users, the salt diffusion will be undetectable. For those users
Merlin RO Assembly
Inlet
Pressure
Pump
If a pressurized tank must be
used, install a diaphragm-style
pressure pump between the
Merlin and the pressurized tank.
Size the pressure pump for Merlin
permeate flow (~ 0.5 gpm).
Pressure pump must have a
pressure switch to control the
pressure in the tank.
To Point of Use
Pressure
Tank