Replacement of valves in the gate valve house of the Schwammenauel dam and hydropower station

1. Introduction

The Rur dam and hydropower station, which banks up the river Rur, was put into operation in 1938 following the completion of its first stage. In the second stage, the dam's crest height was extended to 284.43 m a.s.l., resulting in a maximum storage level of about 71 m. By volume, the Rur dam has the largest storage lake in the district water supply and dam system of Nordeifel and North Rhine Westphalia and the second largest dam in Germany. The lower lake of the dam ensures flood protection and compensation of water shortages. The main tasks of the upper storage lake include raw water supply and power generation. The raw water taken from the storage lake is used for the drinking water supply of the Greater Aachen area. The Francis turbine in the nearby hydropower station of Schwammenauel with a performance of 9.5 MW generates power for peak demands.

2. Feasibility study, invitation to tender and preparation

The dam construction, the pipelines and the valves dated back to the time when the first stage was built. Despite regular maintenance of the valves installed, they showed increasing signs of wear due to aging (picture 1). Within the framework of function tests, the valves turned out to be sluggish and thus difficult to operate. This situation resulted in limited operability of the bottom outlet from the year 2002 on and induced the operator of the dam, the Wasserverband Eifel-Rur (WVER ) in Düren, to commission a feasibility study with market analysis for the repair of the valves in the year 2003. The results of the study showed that the replacement of the valves and actuators would be less expensive than the repair of the old equipment.

By way of public invitation to tender, Heinrich Scheven Anlagen- und Leitungsbau GmbH in Erkrath was commissioned to build the hydraulic steelworks and to supply the new valves including actuators. Heinrich Scheven in turn commissioned VAG Armaturen GmbH in October 2004 to manufacture and supply the valves and pipe adapters.

VAG Armaturen GmbH has over one hundred years of experience in the manufacturing of heavy-duty water supply valves and has been producing butterfly valves and hollow jet valves for more than 50 years. Due to their considerable experience, VAG’s technicians and engineers were closely involved in the project as early as the planning stage.

After the awarding of the contract for the reconstruction and renewal of the hydraulic steelworks in the valve house of the Rur am, the inlet of the bottom outlet pipe was closed with a penstock on the water side of the dam, the bottom outlets were emptied and the old parts of the equipment were removed in mid-June 2005. Now the actual reconstruction work could begin.

3. Requirements

For the selection of the new valves, two criteria were essential:

• The DIN 19700 standard, applicable since June 2004, had to be complied with. This standard requires bottom outlets to have an increased flow capacity of 50 m³ / second for each outlet.
  
• The constructional conditions, which could be changed only to a limited extent, made the difficult installation of the hollow jet valves weighing up to 23 tons even more difficult.

4. Products installed

The calculations made during the planning stage resulted in the selection of the following valves and pipe adapters:

The new hydraulic steelworks equipment consists of two DN 2000 bottom outlets having a DN 2000 pipe adapter serving as a transition pipe adapter from the concrete encased bottom outlet pipes with non-standardised flanges to standardised DIN flanges, a VAG EKN DN 2000 butterfly valve with brake and lift cylinder to prevent pipe bursts, a DN 2000/18000 pipe adapter as a reducer to the nominal width of the hollow jet valves, a DN 1800 dismantling joint to compensate the difference between the face-to-face dimensions, a DN 1800 elbow segment and a VAG DN 1800 hollow jet valve with a downstream venting set having a diameter of 3200 mm and a guide pipe with a diameter of 3600 mm. In the adjacent outdoor pipeline with a diameter of DN 2300 leading to the Schwammenauel hydropower station, a VAG EKN DN 2300 butterfly valve with brake and lift cylinder was installed to prevent pipe bursts. It was combined with a DN 2300 dismantling joint to compensate differences in face-to-face lengths. As a bypass valve for filling the DN 2300 power station pipeline, a VAG RIKO DN 250 plunger valve with downstream venting set was installed (picture 2). The DN 900 air valve dating back to the origins of the dam and made by Bopp & Reuther (now VAG Armaturen) still functioned perfectly so that its replacement was not necessary, which in turn also helped to reduce costs (picture 3).

5. Implementation

In order to meet the DIN 19700 requirements, the old plunger valves were replaced by VAG DN 1800 hollow jet valves with a higher capacity. To ensure their reliable function also at high differential pressures, the two DN 1800 hollow jet valves were manufactured with an additional connecting flange of a nominal width of DN 3200 and wall pipes of the same dimensions. The wall pipes serve as venting devices for the hollow jet valves and are equipped with DN 400 venting pieces leading to the top at a 45° angle on either side. These pieces are connected to DN 400 nominal width pipes taken through the concrete abutment of the outer wall to the top for air intake from outside. Due to the vacuum building up at the seat of the hollow jet valve air is taken in from outside via the ventilation pipes, which prevents cavitation (picture 4).

The hollow jet valves were supplied with pre-assembled wall pipes. During transport the hollow jet valves were protected against distortion by strips of timber in the wall pipes (picture 5). After assembly and alignment of the new operating equipment, the wall pipes including the ventilation pipes were encased in concrete in the new outer wall (1.30 m strength) of the valve house.

For maintenance, the hollow jet valves can be dismantled at any time from the concrete encased wall pipes through the DN 3200 wall flange. After about four weeks, during which the concrete was allowed to harden, the guide pipes with a diameter of 3600 mm were flange-mounted to the wall pipes located in the stilling basin. The guide pipes had to be used to bundle the hollow jet coming out of the hollow jet valves into an even and straight jet as no constructional modifications were allowed in the stilling basin.

The increase in capacity and performance to a total of 100 m³/sec also increased the risk of vibrations in the bottom outlet system when running at full load. After extensive calculations, the engineers dimensioned the wall strengths for both the valves and the pipe adapters for pressure ratings of PN 25 and the flanges for a rated pressure of PN 16.

The installation of the 3 VAG EKN butterfly valves was mainly influenced by the lack of space in the valve house. The safety valves for pipe burst prevention had to be supplied as a welded construction of manufactured steel with a short face-to-face length. Before the disks were manufactured, special models were made to ensure an optimum hydraulic flow pattern.

To ensure the safe emergency closure in case of a pipe burst, special brake and lift cylinders are required. For this purpose, VAG's special brake and lift cylinder system called Hubbremse is used which, in this case was adapted to the restricted space conditions. In case of a pipe burst inside the valve house, the float-controlled devices will transmit the signal for emergency closure of the butterfly valves. The hydraulic cylinders of the brake and lift system installed in the two bottom outlets are installed perpendicularly towards the top. The 2 m long levers for the drop weights of 3000 kg each can be disassembled (picture 6). This construction made the transport to the construction site, the installation in the dam and, of course, also the assembly by Scheven a lot easier.

6. Conclusion

At the beginning of September 2005, after a construction period of just three months, the hydraulic steelworks were completed in time and without any delays. The new valves, which had been factory tested for pressure resistance and proper function at VAG's production facilities in Mannheim (picture 7), were about to prove their reliable function and perfect tightness again during a trial run. After the flooding of the two bottom outlets and the removal of the penstock, the valves were tested in another trial run for proper closure against the water pressure from the storage lake. This proved both the performance capability of the valves and, at the same time, showed an increase of the output quantities of the new VAG hollow jet valves in comparison to the performance calculations (picture 8).

Thanks to the excellent co-operation between the WVER, Heinrich Scheven and VAG-Armaturen GmbH, the dam and hydropower station resumed full operation according to plan in late 2005.

WVER as the owner is convinced to have made the right decision in choosing VAG valves in order to ensure the safe operation of its dam for a long time to come.

7. Literature

1 Factory photos and experience of VAG Armaturen GmbH
2 DVGW energie wasser-praxis 12/2005, by Richard Gronsfeld, Engineer (MSc)
3 WVER Rurtalsperre brochure
4 WVER press release of 1 July 2005