Operation & Maintenance Manual
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P a g e
9.
Operation and Maintenance
9.1 SAND FILTER COMMISSIONING AND OPERATING INSTRUCTIONS
These instructions form part of commissioning and MUST be performed to allow the sand filter to work.
All settings are at the start point and should be verified by further trials after commissioning
The sand filter in this unit will function without attention when the timers are set correctly. It is designed
to backwash automatically at times of low flow. The backwash is by a combination of reverse water flow
and air scour. The times to initiate the backwash sequence are selected by a 7-day time clock. We would
advise that the backwash cycle be initiated during periods of low flow.
For a plant with a minimum of flow during the evening, the time clock should initially be set to start at
04.00 hours and off at 04.04 hours. The time clock is provided with battery backup to retain the settings
during normal short power failures. These times were set at the factory but they should be checked
during commissioning. The time clock selector switch must be in the auto position for the backwash cycle
to work.
The delay timer begins the backwash cycle by operating a solenoid valve to allow the air to flow through
the sand. After the air scour the backwash pump operates until the timer expires.
Ensure that the unit is full, with flow discharging from the sand filter outlet, before starting trials. The
backwash flow rate should be set by adjusting the butterfly valve on the return line.
The correct operation on backwash start-up is as follows:
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Pump draws down the waste level
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The air scour initiates
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The backwash water is drawn from the holding tank around the sand filter body
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The air scour ends
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The pump continues to run until the delay timer switches off or the level sensor on the pump
operates.