Process control for the high lift pumping system is provided by the PCS, through the MTU. The high lift pumps can be operated in automatic (AUTO) mode, and will start and stop based on water level in the 7th Street Reservoir, which represents pressure in the distribution system. An existing pressure transducer at the 7th Street Reservoir measures the water level in the reservoir.
The high lift pumps will operate in manual HAND mode, or automatic AUTO mode to maintain pressure in the distribution system. The plant operation to fill the clearwell and the high lift pump operation to maintain distribution system pressure are independent control strategies. However, due to minimal on-site finished water storage, plant production and high lift pumping are synchronized by operator set points. Generally, the high lift pumping rate will match the plant production rate.
Local Control:
Manual or HAND operation requires selecting HAND from the HAND / OFF / AUTO switch at the MCC. Once the switch is turned to HAND, the pump will start immediately. The pump speed can be adjusted manually at the speed potentiometer located at the local VFD control panel. When a pump is operating in either AUTO or HAND, a high pressure alarm will stop the pump.
PCS Control:
Automatic operation requires that AUTO is selected from the HAND / OFF / AUTO switch at the MCC. When in this mode the PCS system can operate in two modes: PCS Manual and PCS Auto. In Manual mode, the operator starts/stops a pump from the associated PCS screen and sets the speed in manual mode. In Auto mode, the operator must enter a desired clearwell level setpoint. That will ensure that plant potable water is pumped at the WTP facility production rate. The following critical alarms will stop the high lift pumps whether in AUTO or HAND mode:
- A high or high-high level alarm in the 7th Street Reservoir.
- A low or low-low level alarm in the clearwell.
- A low or high level alarm by the chlorine residual analyzer.
Once AUTO is selected along with the desired high lift pumping rate, the PCS will control the operation of the plant based on 7th Street Reservoir level, which will initiate Pump START and Pump STOP, as described in the following table:
| SETPOINT | ACTION ON RISING LEVEL | ACTION ON FALLING LEVEL |
| HIGH, HIGH TANK LEVEL ALARM | 1. STOP ALL PUMPS 2. ANNUNCIATE HIGH, HIGH LEVEL ALARM | – |
| HIGH TANK LEVEL ALARM | 1. STOP ALL PUMPS 2. ANNUNCIATE HIGH LEVEL ALARM | – |
| PUMPS OFF | 1. STOP LEAD PUMP | – |
| PUMPS ON | 1. STOP LAG PUMP, ADJUST SPEED OF LEAD PUMP | 1. START LEAD PUMP, ADJUST SPEED |
| LOW TANK LEVEL ALARM | 1. STOP STANDBY PUMP, ADJUST SPEED OF OTHER PUMPS | 1. START LAG PUMP, ADJUST SPEED OF PUMPS 2. ANNUNCIATE LOW LEVEL ALARM |
| LOW, LOW TANK LEVEL ALARM | – | 1. START STANDBY PUMP, ADJUST SPEED OF PUMPS 2. ANNUNCIATE LOW, LOW LEVEL ALARM |
The PCS rotates the lead, lag and standby pumps with each pump start and controls the speed of the operating pumps based on integral and proportional control. The PCS stops each pump when the operator adjustable pressure limit is reached from the pressure switch. The pumps also stop if the level in clearwell drops below low level setpoint or low level float is activated. The flow meter will indicate and record flow of the pumps. Upon lead pump FAIL, the PCS will initiate startup of the lag pump, and then the standby pump.
The Finished Water flow meter, turbidity and pH are continuously measured by the PCS.
PCS / HMI Configuration:
- Status Display:
- Pump HAND / OFF / AUTO local panel switch indication (each).
- Pump RUN / OFF status (each).
- Pump fault status (each).
- 7th Street Reservoir level indication.
- Finished Water Flow indication.
- Pump speed indication (each).
- Finished Water Turbidity indication.
- Finished Water Chlorine Residual indication.
- Finished Water pH indication.
- Finished Water Pressure indication.
- Operator Entries:
- 7th Street Reservoir lead pump ON setpoint.
- 7th Street Reservoir lead pump OFF setpoint.
- 7th Street Reservoir level alarm setpoints (high-high, high, low, low-low).
- Clearwell level alarm setpoints (high-high, high, low, low-low).
- Clearwell level setpoint.
- Finished Water Turbidity alarm setpoints (high-high and high).
- Finished Water pH alarm setpoints (high and low).
- Chlorine Residual alarm setpoints (high and low).
- High Lift Pumping Speed entry.
- Alarms:
- Pump FAIL (each).
- Finished Water Turbidity ALARM (high-high and high).
- Finished Water pH ALARM (high and low).
- 7th Street Reservoir level ALARM (high-high, high, low, low-low).
- Clearwell Reservoir level ALARM (high-high, high, low, low-low).
- Chlorine Residual ALARM (high and low).
- High Pump Pressure ALARM (each).
- Historical Trending:
- Finished Water Turbidity.
- Finished Water Chlorine Residual.
- Clearwell Level.
- 7th Street Reservoir Level.
- 7th Street Reservoir rate change.
- 7th Street Reservoir valve position.
- High Lift Pump Flow.
- High Lift Pump running.
- Finished Water Flow.