Butterfly valves for refurbishment activities in water treatment plant

In September 2016, AVK Armaturen delivered six double eccentric butterfly valves series 756 in dimensions DN1000 and DN800 for the supply line from the water reservoirs to the clean water pump stations of the Walddörfer Waterworks in Hamburg

The AVK butterfly valves with stainless steel seat ring replace the originally installed butterfly valves from the 1980's. The replacement was necessary due to leakage of the old valves. The refurbishment took place during ongoing daily operation of the plant. Next to the butterfly valves four single-shut-off AVK hydrants series 35/31 were installed for the purpose of air release and intake during filling respectively drainage of the pipe system. The access to the valves and hydrants is granted by AVK plastic surface boxes series 80/30 and 80/31. Thanks to the mix of materials of the plastic body and cast iron lid, the risk of freezing and therefore blocking the lid is eliminated.

At the end of the year, AVK delivered five more double eccentric butterfly valves in DN800. The new butterfly valves replaced gate valves in short length from 1965 placed in the basement of the valve chamber, that is located between two reservoirs. The originally installed gate valves needed to be replaced due to wear. Two of the AVK butterfly valves are actuated by an electric actuator and three of them are manually operated.

The pictures show the valve room before (to the left) and after replacement.

Summary product features of AVK double eccentric butterfly valves
Double eccentric butterfly valves feature a shaft that is offset the centre lines in two directions; eccentricity relates to the centre of the pipeline and double eccentricity relates to the valve centre. Therefore, the disc swings open/closed like a door and ensures a minimum wear of the rubber seal. Furthermore, the special AVK tilted disc design (see picture below) minimises the compression of the disc sealing, which leads to lower operating torques and also minimises the wear of the sealing.

The shaft is connected to the disc by key and keyway. The keyway is additionally secured by two set screws, minimising the wear of the keyway and avoiding the risk of fluttering, that could eventually occur from flow velocity and too much space in the connection as described

In larger dimensions, the disc is fixed by two stainless steel drive dowels that are additionally secured by key and keyway. The dowels are moulded in order to avoid any space occurring between disc and shaft. These features are followed by a perfectly shaped and secured disc sealing, fully encapsulated shaft ends and low friction PTFE shaft bearings, also contributing to low operating torques and long life and reliable function of the valve. The AVK series 756 double eccentric butterfly valves are available with integral ductile iron seat or with a replaceable seat ring of stainless steel sealed with an O-ring.

About the waterworks
Hamburg, situated in the north of Germany, with its 1.734 million inhabitants, has a total of 16 waterworks. Already in the year 1848, a modern water supply system went online in Hamburg. In these times, the main water source used to be the rivers Elbe and Alster. From the beginning of the 20th century, more and more groundwater was sourced from deep rock layers with the help of well-systems, as the raw water was of a very high quality. Drinking water was for the last time ever sourced from the Elbe River in 1964.

Due to an increasing urbanisation in the north of Hamburg and an even faster increasing demand for drinking water supply after World War II, two more waterworks were founded next to the existing one from 1892. One of them was the waterworks Walddörfer, that went online in 1965. The waterworks consists today of 21 wells in an underground depth of 200-380 metres and 11,500 metres of raw water pipelines. The raw water, which is already free of pollution, is treated step-by-step, first by aeration, followed by filtration in 12 closed rapid gravity filters, and is finally led via cascades, where excess carbon dioxide is discharged and another aeration takes place. Finally the drinking water is stored in one of three reservoirs with a total volume of 30,000 m³ storage space. Depending on the individual demand, the water is distributed into the supply pipe system via four pump stations. The waterworks has a daily performance of 38,000 m³ constant load and a peak load of 60,000 m³ drinking water.

Flow chart of water treatment process at Hamburg Walddörfer Waterworks
Source text and picture: Hamburg Wasser

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