General. Suspended solids filtered from feed water will accumulate in the media filter and must be removed in accordance
with the following circumstances.
At least once each day.
Every six hours on rivers and lakes with a lot of organic matter, where turbidity is over 15 NTU and water
temperature is over 70F (21C).
Whenever media filter outlet turbidity increases by more than 0.5 NTU over lowest reading since last backwash.
Whenever the MEDIA FILTER PLUGGED yellow light (1) and horn go on and the media inlet/outlet pressure gage
(2) reading is over 25 psi (172 kPa) differential, (Warning horn should come on).
As specified in shutdown procedures.
Preparation. Prepare for backwashing the media filter as follows:
Pouring the contents of the hypochlorite packet all at once into the tank can cause the
powder to clump together and clog the suction strainer.
Check hypochlorite tank level. If less than nine gallons, add six gallons of product water from the product utility hose and
one packet of hypochlorite and turn on mixer.
Check to be sure that clean/flush tank has 200 gallons (757 I) and one 2-ounce packet of sodium bisulfate was mixed in
Check that air tank air pressure at gage (Item 4, Figure 2-8) is 900 psig (6.2 MPa) or more. If less, wait until pressure
builds to 900 psig (6.2 MPa). If pressure is less than 900 psig (6.2 MPa) and air compressor is not running, troubleshoot
AIR BLANKET blue light (37) must be OFF and media filter level should be below level switch P36.
Refer to Figure 1-11 for illustrations of backwash cycle. Refer to para. 2-34, page 2-156, for
manual backwash instructions if automatic operation fails to function.
Fully open system pressure control valve (Item 3, Figure 2-51).
Push HIGH PRESSURE PUMP STOP (4) and wait for the feed control to drop below 60 gpm (227 Ipm)
Wait for the feed flow meter (5) reading to stop dropping and then push in sequence. CHEMICAL PUMP (7) and RAW
WATER PUMP (8) STOP pushbuttons
Close feed valve (9) almost completely.
If the system pressure control valve is not closed, raw water will back up into the elements
which may cause damage.
Close system pressure control valve (3).
Set OPERATION MODE switch (10) to FILTER BACKWASH.
Push INITIATE (11).
If the feed pressure low alarm sounds, push SYSTEM RESET (12).
The flow rate of 30 gpm (114pm) must be obtained to loosen the packed media beds. Higher
flow rates will result in a loss of media out of the waste hose.
When 2/3 of the flags turn white, the media filter pressure drops below 3 psig (21 kPa), and the raw water pump should
come ON. Adjust the feed valve (9) to obtain a flow rate of 30 gpm (114 Ipm) at flowmeter (5).
As the media filter level drains down, the level indicator (13) flags flip from orange to white
until 2/3 of the flags are white. (Red indicates water level.) If the drain down is not observed
or stops, check the media filter pressure gauge and manually assist the drain down as
· If the pressure is over 5 psig (34 kPa), open the upper drain valve (16). Close when the
raw water pump starts.
· If the pressure is near zero (or falls to near zero) open the lower drain valve (14) and the
vent valve (15). The upper drain valve (16) should be closed. The flags should now flip
showing the drain down. If not, also open the level indicator drain valve (36). Close drain
and vent valves immediately when the raw water pump starts.
· Refer to troubleshooting if the raw water pump still does not start.
Change 12 2-93