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Screenings Removal Controls
Control Strategies PIDs
Screening Control Loop Description Screenings P&ID
Washer Compactor Control Loop Description Washer Compactor P&ID
 
Screening Channel Isolation Gates
Local Manual Control
Isolation gates are manually opened and closed using the manual hand wheels.
 
Perforated Plate Fine Screen
Local Control Panel
The local control panel for each screen has a "Control Power" switch, and a "Screen Local/Off/Remote" (LOR) switch. In addition, each screen has a local Operator Station with a "Screen Slow/Off/Fast" switch, a "Screen Washwater Open/Close/Auto" switch, and an Emergency Stop pushbutton.

The control power switch must be on for the screen to operate.  Placing the screen LOR switch into local will start the screen if either slow or fast is selected on the screen speed switch.  Placing the LOR switch into remote will allow the local PLC to control the operation of the screens.  If both screens are in remote mode, the screens will alternate between the two in a lead lag arrangement.  If one screen is Off, then other screen will run without lead lag operation.
Manual Control
When the screen Local/Off/Remote switch is in the Local position, the screen is controlled from the Slow/Off/Fast switch.  When in Local position, selecting Slow will cause the screen to start at a slow speed.  Selecting Fast will cause the screen to operate at a fast speed, and selecting Off will stop the screen.
The brush and roller will run when the screen runs.
When the Screen Washwater Open/Close/Auto switch is in the Open position, the washwater runs continually.  Placing the Screen Washwater Open/Close/Auto switch in the Close position turns the washwater off.
Auto Control
When the screen Local/Off/Remote switch is in the Remote position, the screen is controlled by the PLC. Place the "Screen Washwater" switch in the Auto position.  The following conditions will start the screen when in Auto mode:
  1. High differential level between the upstream and downstream sides.
  2. Start level on the upstream side.
  3. High level on the upstream side.
  4. High high level on the upstream side.
  5. High level float switch.

High differential or start level will start the lead screen in slow.
High level will start the lead screen in fast.
High high level or the float switch will start both screens in fast.
The screen will continue to run after the levels have returned to normal for the time set in the Screen Run Off Delay timer in the PLC.
If both screens are in remote mode, the screens will alternate between the two in a lead lag arrangement. If one screen is Off, then the other screen will run without lead lag operation.
The brush and roller will run when the screen runs.
The screen washwater will cycle on and off when the screen is running if the Open/Close/Auto switch is in the Auto position.  The cycle time is adjustable on the HMI and can be set to "0" to run the washwater continuously when the screen is running.

Fault Conditions
All screenings removal equipment alarms and fault conditions are displayed on the HMI located on the face of the local control panel. A screen failure, brush failure or a high level send an alarm to SCADA. If an alarm occurs, utilize the appropriate system troubleshooting guide to correct the issue.
 
If an alarm occurs, the local Alarm Reset button must be pushed to clear the alarm and enable the system to return to operation.
 
Washer Compactor
Local Control Station
A local control panel has a "Control Power Off/On" switch and a "Spray Wash Open/Closed/Auto" switch.  In addition, each Washer/Compactor has a local Operator Station with an "Agitator Hand/Off/Auto" switch, a "Spiral Hand/Off/Auto" switch, a "Spiral Rev/Off/For" switch, a "Compaction Zone Washwater Open/Close/Auto" switch, and an Emergency Stop pushbutton.
 
When the agitator is in auto and the spiral is in Auto and Forward, and the washwater sprays are in auto, the washer compactor will automatically start when the screen starts.  Each component of the washer compactor can also be operated manually.
 
Pressing the emergency stop button stops all screen and washer compactor operation. The switch must be pulled back out and the Reset button pushed to enable the screenings system again.
Manual Control
  1. The Spiral will run forward as long as the Spiral HOA switch is in the Hand position and the Spiral ROF switch is in the Forward position.
  2. The Spiral will run in reverse only as long as the Spiral HOA switch is in the Hand position and the Spiral ROF switch is held in the reverse position.  The Spiral ROF switch will spring to the OFF position when released.  The Spiral is intended to run in the reverse direction only for short periods of time to help clear a Spiral jam.
  3. The Spray Wash solenoid valve will open as long as the Spray Wash OCA switch is in the Open position and will be closed when the Spray Wash OCA switch is in the Close position.
  4. The Compaction Zone solenoid valve will open as long as the Compaction Zone Wash OCA switch is in the Open position and will be closed when the Compaction Zone Wash OCA switch is in the Close position.
Auto Control
  1. When the Lead Screen begins running, the Lead Compactor's drain valve will close and its Spray Wash solenoid valve will open.
  2. An ultrasonic level switch monitors the level in the hopper and signals a Start level and High level; a float switch signals a High High level.
  3. The Compactors operate in conjunction with the Screens in a lead/lag arrangement if the Compactor HOA switch is in the Auto position.
  4. The Compactor's Spiral and Agitator start a Normal Wash Cycle when the Start level is reached.  During a Normal Wash Cycle, the Spray Wash solenoid valve closes, the Agitator starts, and the Spiral begin a Scrub sequence.
  5. If a High level is reached, the Compactor stops the Normal Wash Cycle and begins the High Level Wash Cycle.  In this cycle, the drain valve opens, the Agitator starts and the Spiral runs in the forward direction.  This cycle will repeat until the level is below the High level, and then the Normal Wash Cycle will continue.
  6. When the High High level is reached, the Compactor continues to run its High Level Wash Cycle and sends a High High level alarm to SCADA.
  7. When a Spiral High Torque condition is detected, the Spiral will stop, reverse its current direction, stop, and then try to continue in an attempt to clear the jam.  If the jam is not cleared after 3 attempts, the Spiral will stop and set the Spiral Jammed Alarm.  This fault also stops the Agitator and the associated Screen to prevent over-filling.
Fault Conditions
All screenings removal equipment alarms and fault conditions are displayed on the HMI located on the face of the local control panel. A jam, Agitator overload,or a High High level alarm send an alarm to SCADA. If an alarm occurs, utilize the appropriate system troubleshooting guide to correct the issue.
 
If an alarm occurs, the Reset button must be pushed to clear it and enable the system to return to operation.

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Last Updated: 9/16/2013 8:45:35 AM
Version 4.0.1