Flushing devices with storage installations

Flushing devices with storage installations are based on the same hydraulic principle as flushing devices mentioned in chapter 6.4.1. They also create dambreak induced flush waves to clean the sewer but they store the sewage in special structures. Flush valves or flush sluices for example use the main sewers to store the necessary water volume, which generates the flush wave. Flushing devices like gates with flushing chambers or tipping buckets are placed in storm water holding tanks or reservoir sewers in sub-main sewers.

Flushing manholes are used for smaller sewers below 400 mm diameter.

Some installations need fresh water, which is pumped into their reservoir; others use the available rainstorm sewage to fill up the needed flushing volume. Flush tanks work on the siphon principle and store the dry-weather runoff for the flush waves in a manhole.

6.4.3.1 Flush gates with storage chambers

These flushing devices own a special building, the storage chamber, where they stock the water volume for the flush waves to clean large reservoir sewers or storm water holding tanks. The systems can be divided into gate-flushing devices and vacuum-flushing de-vices.

Gate-flushing devices

Gate-flushing devices possess a storage chamber which is filled with storm water sewage.

Therefore the gate in front of the storage chamber needs to be locked. When the reser-voir sewer or the storm water holding is emptied, the gate is opened and the flush wave released. The potential energy of the stored water is transformed into kinetic energy and creates a high velocity flush wave, which runs along the sewer. The gate-flushing system of the Steinhardt company for example is able to clean sewer stretches up to 200 m from deposits. [Steinhardt, 2005] Figure 6.7 shows the principle of the gate-flushing system.

Figure 6.7: Gate-flushing system [Dettmar, 2001]

Vacuum-flushing devices

A modified version of the gate-flushing devices is the vacuum-flushing system of the Biogest company. [Biogest, 2005] The flushing volume held in an airtight storage cham-ber under vacuum conditions. This vacuum above the water column is created by pumps, which are placed on top of the storage chamber. The flushing volume can consist of storm sewage or it can be filled up with fresh water. The maximum flushing distance of this system is around 250 m. Drawbacks of this system are the high noise level created by the air valves when the pressurisation takes place and cost intensive air-tight concrete for the storage chamber. Figure 6.8 shows the principle of the vacuum-flushing device.

Figure 6.8: Vacuum-flushing device [Dettmar, 2001]

Both systems need a flushing sump at the end of the flushing lane to prevent the flushing wave from being reflected. Therefore deposits in end sections of the flushing lanes can be avoided. Because of the detached deposits the volume of the flushing sump needs to be 1.3 times bigger then the water volume that is used for flush waves. Table 6.2 gives an overview on the available flushing systems.

Applications of flush cleaning 97 Product name Producer Type of flushing device

HYDROSELF Steinhardt GmbH Gate-flushing

Klappenlose Schwallspuelung Vollmar GmbH Vacuum-flushing

Typ KS BIOGEST AG Gate-flushing

Typ KS-OF BIOGEST AG Gate-flushing

Typ MF BIOGEST AG Vacuum-flushing

Typ OF BIOGEST AG Vacuum-flushing

Schwallspuelung Niehues GmbH Vacuum-flushing Table 6.2: Flushing devices and producers

6.4.3.2 Tipping bucket

Tipping buckets are usually used to clean storm water retention tanks with flushing lanes up to 50 m and smaller reservoir sewers. Figure 6.9 shows the operating principle.

The bucket is placed at least 2.5 m above the bottom of the tank to obtain the necessary potential energy for a powerful flush wave. When bucket rotates around its axis the water volume is accelerated along the curved back wall to the bottom of the tank. The potential energy of the stored water is transformed into kinetic energy, which forms a flush wave with a high velocity.

Figure 6.9: Tipping bucket [Dettmar, 2001]

At the end of the flushing lane a sump should be installed as mentioned before for the gate-flushing devices. Usually the tipping bucket is filled with fresh water from a well, which makes a pump necessary, but it is also possible to use storm water sewage. Table 6.3 shows different tipping bucket systems and their producers.

Product name Producer HydroSelf Tipping Bucket Steinhardt GmbH

FluidFlush UFT GmbH

HST-AWS HST GmbH

Schwallspueltrommel bgu GmbH

Spuelkippe Vollmar GmbH

Spuelkippe Niehues GmbH

Tipping bucket Copa Limited Table 6.3: Tipping buckets and producers

6.4.3.3 Flush tanks

Flush tanks are some of the oldest flushing devices and usually designed for smaller channels at the beginning of the sewer system. They are placed in manholes where they stock the dry-weather runoff. When the desired volume is reached the device is opened and the flush wave released. Flush tanks like the FABEKUN Spuelschacht or the HydroFlush from the Steinhardt company work on the siphon principle. Other flush tanks like the Spueltopf are arranged in cascades and placed aside the main sewer. They are filled with storm water sewage, which is used for the flushing when the storm event has ended. [Moine & Madiec, 1994]

Figure 6.10: Working principle HydroFlush-Kanalspueler [Steinhardt Wassertechnik, 2005]

Figure 6.10 shows the siphon principle with the HydroFlush device. The dry-weather runoff fills the manhole until the water level reaches the height of the runoff pipe. Then the siphon starts to drain the manhole and a flush wave runs along the connected sewer channel. [Oberlack et al., 2005]

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7 Literature review - Investigations on