The Essential Design Secrets of Pumping Stations: Dead Area, Operational Area, Emergency Storage, and Septicity
Pumping stations are marvels of engineering, quietly keeping essential systems running. However, the details behind their design are often overlooked until something goes wrong. Four critical elements are key to a pumping station’s efficient operation: dead area, operational area, emergency storage, and septicity management. Let’s dive into each and see why they matter more than you might think.
1. Dead Area: The Hidden Hero at the Bottom of the Chamber
One of the lesser-known features in pumping station design is the "dead area" at the bottom of the chamber. Though often ignored, this small design choice is critical for smooth operation.
The dead area is a section of the chamber that always stays filled with water, intentionally keeping the pump volute submerged. This setup prevents air from entering the pump, thereby avoiding a phenomenon called airlock. If air gets trapped in the pump volute, water can’t flow into the pump, which leaves the pump running dry. When this happens, the water level doesn’t change, making float switches ineffective in turning the pump off. Continuous operation ultimately burns out the pump, leading to costly repairs.
Keeping the dead area consistently filled is crucial for proper pump operation. For added protection, some pumps include air release valves that actively prevent airlocks—an invaluable feature to avoid this common issue.
2. Operational Area: Where Daily Pump Cycles Are Carefully Managed
The operational area plays a critical role in the day-to-day function of a pumping station, balancing efficiency with durability. Here’s why it matters:
The operational area is where regular pump cycles are managed. Pumps need to run frequently enough to keep sewage moving and prevent stagnation, which, over time, can lead to septicity. If sewage sits for more than six hours, it risks going septic, creating damage and hazardous gases. However, over-pumping also wears equipment out quickly. Limiting pump cycles to no more than 15 times per hour prevents excess strain and prolongs the life of the pumps.
Getting this balance right is key to a reliable and low-maintenance pumping station.
3. Emergency Storage: The Last Line of Defense
In pumping station design, emergency storage is often misunderstood as simply the chamber’s total storage capacity. However, true emergency storage starts above both the dead area and the operational area and reaches up to the bottom of the lowest invert level (bottom of the lowest incoming pipe).
Emergency storage only activates in the case of mechanical failure or in cases of excess inflow's above and beyond what the pumping station has been designed to cater for. This setup ensures a dedicated buffer zone if something goes wrong, giving operators time to address issues before an overflow occurs. Emergency storage is particularly important in setups where the pumping station is located at a low point; in these cases, careful drainage connections must be made to avoid backup during high inflow. This consideration can prevent costly operational headaches, especially during heavy rainfall or peak demand.
In some cases, the emergency storage can include the pipework and manhole network leading up to the pumping station, which can be flooded up to what is known as the flood level (as shown in the image below)to allow for extra emergency storage. This can be used on sites where the pumping station is situated on the lowest part of the site where the site slopes back towards the location of the pumping station or where there are restrictions on the depth of the pump chamber due to the ground conditions or planning restrictions.
4. Septicity: The Hard Truth About Sewage Stagnation
Septicity in pumping stations goes beyond unpleasant odors; it’s a matter of safety, infrastructure longevity, and operational efficiency. If sewage sits stagnant in the chamber for more than six hours, it begins to go septic. This not only produces harmful gases but also corrodes equipment and poses serious health risks.
Avoiding Septicity Requires a Delicate Balance:
Size the Operational Area Carefully: Ensure the chamber’s capacity matches the incoming flow rate. Oversizing the chamber causes sewage to stagnate, while an undersized chamber may result in pump overrun or even dry operation.
Limit Pump Cycles: Too many cycles wear out pumps quickly, while too few can allow septicity to develop. Aim for a balance that limits pump cycles to around 15 per hour.
Optimize the Rising Main: Oversizing the rising main, particularly on long runs, increases sewage retention time, which can accelerate septicity. Right-sizing this component is essential.
Following these practices keeps pumps running smoothly, reduces maintenance costs, and supports the station’s safe and efficient operation.
In Conclusion: Design Details That Make a Difference
When designed with care, these often-overlooked elements—dead areas, operational area, emergency storage, and septicity management—become the unsung heroes of pumping stations. Each component plays a critical role in ensuring pumps don’t run dry, sewage stays fresh, and emergency situations are manageable. By optimizing these areas, we can reduce maintenance, extend pump life, and ensure safe, efficient operation.
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