There are numerous areas where topology dictates the sewage flows have to defy gravity through the creation of “rising main sewer networks”. That is where the sewage flows into a well commonly referred to as a “wet well” containing submersed pumps, where the pumps are used to empty the wells under the control of a level transducer or float switches.
However, if the downstream sewer network is stressed, subject to hydraulic overload this can lead to sewer flooding, surcharges, or the operation of CSO overflows if the switching of the pumps is not optimised in real-time to clip the peak loading at these “hotspots”.
Control requires single or several level sensors installed at or near the hotspot in the sewer network to provide feedback, communicating in virtual real-time back to the pumping station, to produce a pump inhibit. As the majority of the hotspots are remote, devoid of power, and liable to flooding, the level transducer must be one that is capable of operation from batteries, have a fast reporting rate, and most importantly be tolerant of total submersion.
RDN’s BDT level transducer ticks all these boxes and as a consequence has been used for over a decade to provide pump inhibits, by the likes of Anglian Water and various industrial companies to upgrade their wet well pump controllers to make them smart.
Normally the BDT transducer is installed in a chamber near to the hotspot and its sensors trigger point is set to a level just below the critical point. A telemetry repeater (Booster) is also installed on street furniture or in a bollard adjacent to the chamber, which captures and relays the BDTs signal back to the pumping station in virtual real-time. This makes the system independent of cellular networks and the internet. The communication used in the UK is normally Ofcom licenced making certain there is no interference from other users.
The broadcast inhibit signal is received at the pumping station by one of RDN’s Gateway receivers which it operates a relay to provide the pump inhibit signal to the pump’s controller.
Where more than one pumping station with wet wells feeds the same sewer additional gateways can be installed to replicate the BDT level signal at each of the pumping stations.
For clarity, inhibit does not necessarily mean totally stopping pumping, but maybe the reduction of the rate of pumping. If the pump has speed control, then reduce speed. If there are multiple pumps in parallel, then use one rather than two pumps. Or if there is no control, switching on and off of the pumps to modulate the flow. In all cases we recommend that the normal well full stitching point is lowered at the commencement of the project, to provide more storage capacity during periods of inhibition.
Advantages of BDT Telemetry-Based Pump Inhibit System
For example, a rainfall intensity sensor can be used to trigger the pre-emptying of the wet wells to ensure that there is the maximum capacity for storage. This has been found to be more accurate than using rain radar and also provides a degree of autonomy should the service fail.
Pumping stations can be interlocked and synchronised using real-time telemetry between stations whereby stations are prevented from emptying their contents at the same time. Often this includes a PLC that sets the time delay to allow for flow transit times. RDN has a range of gateways that can both receive inhibit signals and also relay inhibits between pumping stations.
Since the introduction of the BDT in 2010, Radio Data Networks is proud to have supplied dozens of inhibit systems to utilities across the UK.
Simply, the BDT and RDN’s telemetry provides a low-cost, low-carbon, retrofit intervention in the toolbox for reducing the occurrence of sewer flooding and the activation of CSO overflows in sewer networks fed by rising main sewers.