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Stormwater Management Pump station operation Operation of storm drainage pumps is sequenced with the water level in the wet well. Each pump starts and stops automatically when the water level in the wet well reaches the set points. An ultrasonic level transducer and a backup pressure level transmitter in the well continuously monitor water levels and send this data to the main programmable logic control (PLC) to direct the operating sequence of pumps. The operator should have the capability of initiating an automatic duty rotation of the pumps, or taking the pumps out of service. An ultrasonic level transducer is to be the primary controller and a pressure level transmitter is to be provided for redundancy. The operator should be able to select either the ultrasonic level sensor or pressure level transmitter to be used in the wet well for control purposes. If there is a loss of echo and the primary level sensor is unreliable, the standby pressure level transmitter alone will be used for control. In addition to the ultrasonic control and pressure level transmitter, five floats will act as a backup for an emer-
gency, or PLC failure. (See Figure 5) In the event of a pump failure, an alarm is activated and the next pump in the duty sequence will begin to operate. Check valve proximity switches are used to ‘prove flow’ for the pumps. In the event the pump is called on to start, and there is ‘no flow’ indicated at the check valve, the pump shuts down, an alarm is generated and the next pump in the duty sequence begins to operate. As water level in the wet well rises to a set elevation, the first pump in the duty pump sequence starts. When it is running and the water level drops to a set elevation, the pump shuts down. When it is running and the water level rises to a set elevation, the pump which is second in the duty sequence is triggered. When both first and second duty pumps are running and the water level rises to a set elevation, the HWL emergency alarm activates and, if the first duty pump fails then the pump which is next in duty sequence starts. Should the water level continue to rise, the HHWL emergency alarm activates and, if the second duty pump fails, then the pump which is next
in the sequence starts. Pumps are programmed to start and shut down at defined elevations in order to keep the upstream convergence MH from surcharging. When all duty pumps are running and the water level drops to a set elevation, the last duty pump shuts down first. As the water level continues to drop to set elevations, the duty pumps shut down one after another. The first duty pump shuts down last. The information discussed here is intended to be a useful tool for anyone who deals with the design of new or upgrade of existing gravity sewer, pressure sewer, pump selection and pump station operation. It is based on general information from the Windsor-Essex Parkway project that will be operated by Windsor Essex Mobility Group, with the support of Infrastructure Ontario and the Ontario Ministry of Transportation. Jahangir Chowdhury is with Hatch Mott MacDonald Group, E-mail: Jahangir.chowdhury@hatchmott.com
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Introducing David Merriman, Senior Waste Management Consultant
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Phone: 610-236-1100 Email: stormwater@brentwoodindustries.com Web: www.brentwoodindustries.com
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