c. Function of ROWPU Main Components.
(1) Water intake. The suction hose strainer prevents large pieces of trash
from entering the system; whiIe the float holds the suction hose strainer between
surface and bottom of the raw water source. The raw water pump draws raw water
through the suction hose strainer and sends it under pressure to the multimedia fiIter.
(2) Chemical input. The chemical feed metering pump assembly draws
chemical solutions from cans and injects them into water at various points in the
purification system. The chemical feed metering pump motor provides power for four
chemical feed metering pump drive units that are illustrated in figure 5-23. These units
are as follows:
(a) The Polymer drive unit adds polymer solution to raw water.
Polymer solution collects small pieces of floating solid matter into groups large enough
to be removed by the multimedia fiIter. This is a clear tube with inside support.
(b) The sodium hex drive unit adds sodium hex to raw water. Sodium
hex prevents scaling. This is a yellow tube.
(c) The citric acid drive unit adds citric acid to output of multimedia
fiIter prior to ROWPU shutdown. Citric acid removes scaling developed in the system
during operation. This is a black tube.
(d) The chlorine feed pump uses calcium hypochloride to disinfect the
water. This is a regular clear tube.
(3) FiItration. The raw water flow meter indicates the rate of flow of water
drawn in by raw water pumps. The backwash valve, in the normal position, allows raw
water to enter the multimedia fiIter and closes the backwash Iine. When the backwash
valve is in the backwash position, it allows brine to enter the multimedia fiIter and closes
the raw water line. There are two stages of fiItration. These stages are:
(a) First filtration stage. The multimedia fiIter control valve (MMFCV)
routes the flow of water into and out of the multimedia fiIter. During normal ROWPU
operation, the MMFCV raw water from the backwash valve to the top of the multimedia
fiIter whiIe routing fiItered output from the bottom of the multimedia fiIter to the booster
pump. During backwash, the MMFCV routes two flows of water. It routes brine from
the backwash valve to the bottom of the multimedia fiIter as it routes contaminated
water from the top of the multimedia fiIter out of the ROWPU, through the waste outlet
on the front panel. The MMFVC also changes the flow rate during different stages of
backwash. The multimedia fiIter performs the first stage of fiItration. It removes most of
the dissolved solids. The multimedia fiIter gage indicates differential pressure across
the multimedia fiIter. The vent multimedia fiIter valve releases air from the multimedia
fiIter whiIe the fiIter is fiIIing during the ROWPU startup. The booster pump forces
output of multimedia filter through the cartridge filter.