This week, we will cover back-up sensors for lift stations. In the past, we have given an overview of lift station sensors, and discussed both simplex and duplex lift station configurations.
Modern lift stations use a variety of different methods for controlling pumps. Whether the lift station is using a single pump, or several, keeping them running optimally is extremely important. Equally important is having an effective and reliable back-up system to prevent sanitary sewer overflows (SSOs).
The different control methods used in lift stations include relay logic, proprietary controllers and programmable logic controllers. When any of these fail, it often results in an overflow of sewage – resulting in a major health risk for citizens, as well as fines, penalties and cleanup costs for the utility.
Steve Brown of Advanced Automation Products, Inc in Florida is an expert in lift stations. He’s seen it all, and notes that,
“In addition to controller failures, sensors also fail due to wear, component failure, power issues and improper maintenance. Additionally, floats can tangle, grease can build up, there can be rodent issues and other issues can occur in the wet well.”
Needless to say, back-up controls are essential. There are several methods of automatic back-up that start pumps in the case of primary control system failure. We will cover two simple examples that are both cost effective and reliable. Both run independently of the primary controls.
In the first case, two floats are suspended above the high-level alarm to control the on and off switch for the back-up pump. Steve explains:
“When the level rises to the point where the override float changes to an ‘on’ state, one of the pumps will begin to run. This pump will continue to run until the level is pumped down to the point when the off float changes state.
“This is commonly used, is simple in design, but does need to be designed into the control panel, or the control panel must be modified to include the right relays and terminals for wiring the floats.”
In case two, the inconvenience of modifying a control panel doesn’t exist. In fact, in this case, only one float switch is needed – saving money on the purchase, installation, and maintenance. Steve recommends this to his customers to help them reduce cost and downtime. He elaborates:
“In this example, the float provides the complete backup control without the need for panel modifications or design. The KA-2H or KA-M2H float switches are 2 wire floats that have built in hysteresis between the on level and the off level of the float.
“The float would be suspended at the desirable level in the wet well and wired into the panel. The first wire would be connected to control voltage and the other to the appropriate terminal on the motor starter or run relay.”
The KA float switches are, of course, capable of controlling a single pump, carrying control voltage up to 6 Amps at 250VAC. They provide reliable back-up pump control that reduces cost and saves utilities all the risk, hassle, and cost of an overflow.
Have you ever seen a sanitary sewer overflow? Have you ever had to clean one up? If you have experience with either lift station control systems, or the result of an SSO, we’d love to hear from you!
As always, let us know if you have any questions about the above application by contacting our application engineers directly.
