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2.2.1 Backwash Set Point
DP switch showing adjusting screws
The DP set point may be adjusted by turning the
adjusting nut located inside the switch cover. Turning
this nut will alter the setting on the indicating gauge
located on the outside of the switch. This indicator is
for reference only. The actual differential pressure at
which the switch operates is determined by calculating
the difference between the inlet and outlet pressure
gauges.
It is imperative that the clean DP of the filter be
ascertained prior to setting the backwash set point on
the switch. To set the DP set point, determine the
maximum acceptable DP that the filter can impose on
the overall system and set the switch accordingly.
Note, the closer the backwash set point is to the filter’s
clean DP, the more frequent the filter will backwash. It is usually necessary to try a number
of settings until the best compromise is reached.
Maximum setting for the DP switch is
40 psi
.
The DP switch is factory set at approximately 10 psi.
Note: For effective cleaning, the
filter requires a minimum of 30 psi on the discharge side of the filter at time of
backwash.
2.2.2 High Set Point
The High set point is adjusted by the second adjusting nut located in the DP switch, situated
on the right hand side of the switch. When making adjustments to this setting it is
imperative that the setting is not to close to the backwash setting. This will avoid a false
alarm condition during a backwash sequence. Normally a difference of 10 psi should be
sufficient between both settings.
2.3 Backwash Duration Timer
The backwash duration is the amount of time each pod is backwashed. The backwash
duration is the length of time the Indexing Valve Shoe remains stationary at each pod and
the time that the pneumatic Backwash Valve remains open. This is how adjustments are
made to achieve optimum backwash efficiency. The backwash duration can be set as low
as 2 seconds without hindering backwash efficiency, and is dependent upon system
pressure. The backwash duration is factory set to 3 seconds and this setting is
recommended for most applications. The longer the duration, the longer the remaining five
elements are “on line” before they are cleaned. Therefore, at some point, a full cleaning of
the filtering elements will be impaired.
The objective when setting the backwash duration is to find the optimum balance between
low backwash wastewater and full element cleaning. Full element cleaning is demonstrated