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Grit Removal System Controls
Control Strategies PIDs
    Grit System
Grit Removal System
Grit Chamber Paddle Mechanism, Grit Chamber Blower, Grit Pumps and Grit Classifier
Local Manual Control

When the grit chamber paddle mechanism Hand/Off/Auto switch is in the Hand position, the paddle runs continuously.
When the grit chamber paddle mechanism Hand/Off/Auto switch is in the Off position, the paddle stops.

When the grit classifier Hand/Off/Auto switch is in the Hand position, the grit classifier runs continuously.
When the grit classifier Hand/Off/Auto switch is in the Off position, the grit classifier stops.

When the grit pump Hand/Off/Auto switch is in the Hand position, the grit pump runs continuously.
When the grit pump Hand/Off/Auto switch is in the Off position, the grit pump stops.

When the grit chamber blower Hand/Off/Auto switch is in the Hand position, the blower runs continuously.
When the grit chamber blower Hand/Off/Auto switch is in the Off position, the blower stops.

SCADA Auto Control

When the Hand/Off/Auto switch for the grit chamber paddle mechanism, grit classifier and grit pump is in the Auto position the PLC controls this equipment as follows:

1. The grit chamber blower starts to fluidize the grit. This will run for a set period of time selectable by the operator through the PCMS.

2. After a set period of time (about 60 seconds, selectable by the operator through the PCMS) a signal is sent from the PLC to start the grit pump. One minute after the grit pump is called to run, the PLC will also send a signal to start the grit classifier. The grit pump will run for a set period of time (5 minutes). The grit classifier will run for a set period of time (6 minutes).

3. The grit removal cycle can operate for only one grit chamber at a time, be­cause the single grit classifier is not expected to have sufficient capacity for grit from both chambers simultaneously.

4. If the PLC detects the grit chamber blowers HOA switches are not in the auto position, the rest of the grit removal cycle will still operate.

5. If the PLC detects that the grit pump or grit classifier HOA switches are not in the AUTO position, the grit removal cycle will not operate.

6. If at any time during a grit removal cycle the PLC detects equipment that (1) has its HOA switch in the AUTO position, and (2) has an Off status when it should be an On status, the PLC will halt the grit removal cycle and output a GRIT SYSTEM FAILURE alarm to the HCP annunciator. Toggling of hand switch HS‑5071 in the screenings loading area to the Off position will reset the alarm.


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Last Updated: 9/16/2013 9:03:06 AM
Version 4.0.1