StormBlaster™ rotary jet cleaners are highly versatile and can effectively clean a wide range of stormwater attenuation tanks. The systems are designed with various nozzle sizes, which result in different jet lengths and flow rates. They can operate at different pressures, and we often install multiple units to clean larger tanks. Over the years, we’ve developed a set of protocols for designing systems that can clean nearly any storm tank. However, there are some tank types that may not be suitable for cleaning, and we have addressed these in another video. In this article, we’ll outline the key factors to consider when sizing a StormBlaster™ system to ensure it cleans a storm tank effectively.

1. Jet Length

Each StormBlaster™ unit operates at a specific fluid pressure and has a particular nozzle size, which determines its effective cleaning jet length. Ideally, the cleaner should be positioned at the top of the tank, centrally, to maximise the area covered by the jet. This positioning ensures that more of the tank is within the range of the cleaning jet.

To determine the effective jet range, measure the distance from the nozzle to the furthest point the jet will clean. Ensure this distance is within the specified range for optimal cleaning coverage. While it may not always be possible to achieve ideal positioning, particularly in open tanks, this is an important factor to consider.

Effective jet lengths and flow rates:

• 2 × 6 mm: Jet length 11 m, Flow rate 14 l/min
• 2 × 7 mm: Jet length 18.9 m, Flow rate 22.6 l/min
• 2 × 8 mm: Jet length 25.5 m, Flow rate 40 l/min
• 2 × 10 mm: Jet length 31.6 m, Flow rate 81 l/min
• 2 × 12 mm: Jet length 47.5 m, Flow rate 142 l/min
• 2 × 14 mm: Jet length 57 m, Flow rate 228 l/min

2. Water Usage

Each rotary jet cleaner operates through a cleaning cycle, which has a flow rate depending on the pressure at which it’s running. The cleaning cycle must be completed to ensure every part of the tank is cleaned. To calculate the total water usage per cleaning head, multiply the cleaning cycle time by the flow rate.

Wash cycle times by pressure:

• 2 bar: 85 min
• 4 bar: 50–72 min
• 6 bar: 36–60 min
• 8 bar: 29–48 min
• 10 bar: 26–37 min

Although it may be tempting to reduce water usage, there are design criteria that must be followed. It’s essential to use a minimum amount of water per square metre of the tank floor to ensure effective drainage within the system. While we aim to reduce water consumption, there’s a limit to how much can be reduced without compromising cleaning efficiency.

3. Pumps and Pressure

Ideally, each cleaning head should operate at a fluid pressure of 8 to 10 bar. This pressure range increases the overall flow rate through the nozzles and reduces cleaning cycle time, meaning the tank is cleaned faster. Additionally, operating at this pressure allows the system to be more efficient, using less water while providing more powerful jets for better cleaning performance.

Achieving this pressure often requires the installation of a booster pump to ensure optimal fluid pressure and flow rate on-site. The system is most effective when running at 8 to 10 bar.

4. Multiple Tank Cleaners for Larger Tanks

For larger tanks, we often divide the tank into smaller, virtual sections, each cleaned by its own StormBlaster™ unit. This method ensures that each section of the tank is within range of the cleaning jet and adheres to the design protocols. There are no physical modifications to the tank; instead, the sections are defined on the design drawings. The cleaning jets may overlap slightly into adjacent virtual sections, providing additional cleaning benefits.

Running multiple cleaners in sequence, rather than simultaneously, reduces the pump duty and ensures that each unit receives the correct flow rate and pressure for optimal performance. For example, if there are four StormBlasters in a large tank, running them sequentially requires only the necessary flow rate and pressure for each individual unit, rather than four times the required capacity. This method reduces the overall strain on the pump and improves efficiency.

5. Positioning and Access

Proper positioning is crucial for effective tank cleaning. Ideally, tank cleaners should be centrally positioned to ensure the cleaning jet can cover the maximum area. In roof tanks, this is easier to achieve as cleaners can be placed directly through the roof and accessed via a manhole cover.

For open tanks, positioning is more challenging due to their width. In such cases, we typically position the cleaner on a swing arm, allowing it to be moved to the side for maintenance. However, the practical length of these swing arms is typically limited to 2–3 metres, which may not be sufficient for tanks wider than 6 metres. In these instances, positioning the cleaner centrally may not be possible, but alternative design adjustments can still ensure effective cleaning.

Conclusion

These design considerations have been developed over the past eight years of deploying StormBlaster™ systems across the UK, France and Ireland. By following these protocols, we have installed approximately 130 systems that consistently deliver effective cleaning of stormwater attenuation tanks.

Whether you’re designing a system for a small or large tank, these guidelines will help ensure that your StormBlaster™ system delivers the most efficient and thorough cleaning possible. With careful attention to factors like jet length, water usage, pressure, and positioning, you can optimise the performance of your system and maintain effective storm tank cleaning.