Renovation and new construction of stormwater tanks with 4.0 equipment
Development of discharge controls
Stormwater tanks are used to store runoff peaks during precipitation. For this purpose, the quantities of water flowing into the stormwater tank to create a back-up from the sewer must be limited. At the beginning of the rainwater basin era, static flow restrictors in the form of smaller throttle pipes (Fig. 1) or throttle valves (Fig. 2) were used to limit the flow rates. The cross-section of the pipe or valve was dimensioned in such a way that the maximum upwardly limited runoff water volume was achieved at the maximum impoundment height in the stormwater tank. As the discharge is a function of the impoundment height, this means that at lower impoundment heights, lower volumes of water than the target volume also flow out of the stormwater tank. Without countermeasures, this results in the stormwater tank taking longer to empty. Time is lost and the basin volume is not optimally utilized.
In order to maintain the setpoint flow rate as constant as possible, even with different impoundment heights in the stormwater tanks, flow regulators were developed instead of flow limiters, which always maintained the same constant flow rate regardless of the impoundment height or the water level height in the stormwater tank. This property was expressed by the so-called selectivity based on the Q/H characteristic curve (Fig. 3). These flow regulators, or still called throttling devices, were initially purely mechanical constructions that used float mechanisms to detect the backwater or discharge conditions and mechanically reduced or widened the discharge opening from the stormwater tank in order to achieve the target discharge. (Fig. 4+5)
Over time, these purely mechanical controllers were increasingly replaced by electromechanical controllers. The reason for this development was:
- the increasing electrification of the rainwater basins themselves,
- the desire for continuous measurements, adjustable target values and
- the possibility of intervening on site or remotely in the event of relocation or malfunctions
Today, a selection of electromechanical discharge controllers have been developed and established, which continuously record the water level and/or velocity using sensors (ultrasonic/radar/magnetic-inductive) and automatically move shut-off devices to the correct position for the target discharge depending on the level of water or flow rate. For further guidance in the selection of suitable discharge control systems, we will discuss the specific requirements and solutions in connection with the application in stormwater tanks below. HST-Zangenberg has the most comprehensive complete range in the field of flow control.
Installation dimensions or required shaft sizes
When retrofitting or renovating, the compact dimensions of flow regulators can be an advantage or a defining feature, e.g. if the construction of a new manhole is out of the question for reasons of space or cost. In such cases, the HST HydroMat-E (Fig. 7) and the Alligator (Fig. 9) from HST-Zangenberg are the solution.
The HST HydroMat-E is characterized by minimal structural dimensions and investment as well as the possibility of wet installation in the headwater. The discharge values are determined from the measured levels in the headwater and/or tailwater. If a more precise and reliable flow measurement is required, the Alligator from HST-Zangenberg with magnetic inductive flow meter and pneumatic control flap is used. It combines compact dimensions with precise and reliable magnetic-inductive flow measurement.
Measuring and control accuracy
Another key aspect that determines the choice of system is the need to record the flow rate accurately and reliably. It is also necessary to consider whether and to what extent an operating mode with partial filling should also be taken into account. Inductive full-fill meters as a component of a flow control system, such as Alligator (Fig. 9, 10, 12), Anaconda (Fig. 11, 14) and HydroMat-Q (Fig. 7), are extremely reliable in terms of continuous flow measurement when used correctly, especially if the entire system has been calibrated at the factory. Full filling is generated by culverting or temporary accumulation in the straight pipe. This in turn requires precautions to prevent and remove deposits, as is the case with Alligator and Anaconda.
When using partial fill meters in discharge control systems, reliable flow measurement can only be achieved in conjunction with application calibration and continuous monitoring. The HST-Zangenberg Anacondas are our clear favorite for new constructions or where there is sufficient space in the manhole structure and the highest demands are placed on accuracy and operational reliability. Thanks to the pneumatic pinch valves (Fig. 13, 14) as shut-off and control elements, it is the safest and most reliable solution in the wastewater sector due to its absolute accessibility. If you also want to measure continuously not only during full filling but also during partial filling, you can expand the above-mentioned systems with an EMA system or the EMA function or use a HydroMat-Q or HQ solution. In this configuration, for example, very small quantities can be recorded and thus external water can be determined.
EMA systems (electronic digital quantity evaluation) use a current measured value for partial filling, data and statistics to determine the exact flow value and also enable the plausibility check of flow data and self-calibration of discharge measurements and controllers. HydroMat-HQ systems are based on partial filling measurement methods with level and velocity and are available with hydraulically optimized parabolic or eecan sections to increase measurement accuracy. This makes partial filling a measurable and recordable variable even for small dry weather quantities.
Operation and maintenance
Of course, there are also some aspects or issues to consider when it comes to the operation and maintenance of stormwater tank outflow regulators, such as
- operability and operating options on site or remotely
- Recording and monitoring of all process and operating data on site or remotely
- Statutory audits based on self-monitoring and self-monitoring regulations
- Options for continuous and self-calibration
- the advantages and disadvantages of wet or dry installation
- Accessibility to sensors and actuators
- Emergency operation options (emergency circulation and emergency operation)
Thanks to our IntelliFlow and SCADA.web extensions, upgrades of existing installations to 4.0 equipment are also recommended
Operation and maintenance
The SCADA.web extension provides alarms in the event of faults, displays the current process status and provides all process data. In addition to measurement, the IntelliFlow extension determines flow data in parallel, compares and checks the plausibility of this data and even enables automatic volumetric calibration if the structural conditions are suitable.
The IntelliNet extension enables complete automation and integration into 4.0 network management
Application examples
Middle Wiesental Wastewater Association
A flap in front of a screw lift was to be replaced. In an extremely confined space, a reliable control system was sought that would also function under water during operation.
As the system was to be used at the inlet, automatic self-cleaning and a simple cleaning option were prerequisites for a functioning everyday solution.
The short Alligator directly upstream of the screw lift combines the shortest possible length with reliable control performance. The Alligator is optimally adjusted to the requirements of heavily contaminated wastewater thanks to its automatic flushing surge and the fast folding up of the entire system.
Erftverband Bergheim
A flap in front of a screw lift was to be replaced. In an extremely confined space, a reliable control system was sought that would also function under water during operation.
As the system was to be used at the inlet, automatic self-cleaning and a simple cleaning option were prerequisites for a functioning everyday solution.
The short Alligator directly upstream of the screw lift combines the shortest possible length with reliable control performance. The Alligator is optimally adjusted to the requirements of heavily contaminated wastewater thanks to its automatic flushing impulse and the fast folding up of the entire system.
