(b) Second filtration stage. The cartridge fiIter performs the second
stage of fiItration by removing very small dissolved solids. The cartridge fiIter gage
indicates differential pressure across the cartridge fiIter. The vent cartridge fiIter valve
releases air from the cartridge fiIter whiIe the fiIter is fiIIing during ROWPU startup. A
low-pressure switch senses pressure in the output Iine from the cartridge fiIter. When
the Iine pressure drops below 10 psi this causes the reverse osmosis pump to shut
down and the reverse osmosis pump low-pressure indicator to light.
(c) Third filtration stage. The reverse osmosis pump develops high
pressure needed to force output of the cartridge fiIter through the reverse osmosis
elements. A rupture disk ruptures to relieve pressure if pressure reaches 1425 psi, as
indicated on the reverse osmosis pressure psi gage. This rupture prevents damage to
the system if the high-pressure relief valve faiIs to open and/or if the high-pressure
switch faiIs to shut down the reverse osmosis pump. The pulse damper reduces the
pulsing effect of the reverse osmosis pump. It also smooths the flow of water through
the reverse osmosis elements. The vent pulse dampener valve releases air from the
pulse dampener whiIe the pulse dampener is fiIIing during the reverse osmosis startup.
The high-pressure relief valve opens to relieve pressure if the pressure in the Iine,
between the pulse dampener and the reverse osmosis elements goes above 1100 psi.
There is a high-pressure switch, which senses pressure in the Iine between the pulse
dampener and the reverse osmosis elements. If pressure rises above 1250 psi and the
high-pressure relief valve fails to open, this causes the reverse osmosis pump to shut
down and the reverse osmosis pump high-pressure indicator to Iight. The reverse
osmosis pressure psi gage indicates output pressure of the reverse osmosis pump.
The reverse osmosis elements perform the final stage in fiItration. Water from the pulse
dampener flows into the outer shell of one pressure vessel. Inside the pressure vessel,
pure water is forced into the two-fiIter elements through their permeable membrane
surfaces. Water, stiII containing foreign matter, flows through the other three pressure
vessels in series. In each pressure vessel, pure water is forced into the fiIter elements.
The remaining unfiItered water (brine) flows out of the ROWPU for storage in the
backwash water tank. Pure water flows out of the center of each pair of fiIter elements
into a common pipe that carries the water out of the ROWPU for storage in the product
water tanks. Connections between pressure vessels are different in the two models, but
the operation is identical. The reverse osmosis vessels gage indicates differential
pressure across the reverse osmosis elements.
(4) Brine collection. The brine flow meter indicates the salt of brine flow out
to the backwash water tank. The backwash water tank collects the water rejected by
cleaning the reverse osmosis elements. ControlIing the flow of brine from the backwash
water tank is the backwash tank valve. The backwash pump forces brine backward
dumped out of the ROWPU through the waste hoses. When the backwash cycle is
complete, the output from the backwash pump is connected to the vent vessels Iine.
Brine mixed with citric acid is then forced through the reverse osmosis elements to
clean them. The solution is returned to the backwash water tank and recirculated by the