Water.DOC 11/8/99 Filter Backwash Demonstration
The filter has three stages of operation:
Initialization:
This sets initial conditions. All the valves are closed, all motors are turned off and the tank level is at zero.
In Service:
The raw water is filled to 98% of the tank volume to provide adequate pressure for outgoing clean water.
The high level alarm opens the clean water valve, and level and flow are maintained at steady values. This
continues as long as the filter head pressure is within the allowable limits. All other valves remain closed
and pumps are off.
Backwash:
When the pressure crosses the limit, the backwash sequence is activated as follows:
1. The raw water valve is closed, and the clear water valve remains open till water level reaches zero.
2. When the level is zero, the air scour valve opens and air blower pump is turned on. Air is blown into
the filter, dislodging the solids which are removed through a drain valve.
3. Air blowing is then stopped and wash water is allowed in to fill the tank to 5% of the total level by
opening the wash water valve.
4. The drain valve is opened to let out dirty water and broken-up solids.
5. The wash water pump is then turned off, the level decreases to zero and backwash is complete.
Demonstration Guide
The MOD 30ML is performing the process simulation as well as the filter control and backwash sequence.
One analog input is used to simulate header pressure.
If the MOD 30ML demonstration kit is NOT used, the I/O should be disabled. To do this, use the TAG
key to scroll to the SIMULAT display and use the arrow keys to make sure it shows DISABLE. When the
I/O is disabled, all load changes can be made from their corresponding faceplate displays using the ramp
keys. The simulation will disregard any I/O that is connected to the instrument.
Load Changes
In order to create the situation necessary for backwash, the following disturbance can be introduced:
Pot #1 - header pressure
If the demonstration box is not used, the header pressure can be manipulated from the appropriate front
panel display using the ramp keys.
Alarms
Two alarms are configured to provide operator notification:
Loss of header pressure 91%
Backwash required > 98%
Operator Changes
The following operations may be done from the front panel display:
Put filter in service
Clear totalizer (clean water)
Manipulate header pressure
Initiate backwash sequence
