With its history dating back to 1872, the valve manufacturer VAG Armaturen GmbH Germany has a long tradition in the field of dams and hydropower – not only in Germany but globally. For more than 140 years the company has been offering valves and gates for municipal water supply, sewage, industrial markets, dams and hydropower. It has been one of the pioneers in the valve market with a focus on innovative solutions and it is a global brand when it comes to applications like bottom outlets of dams, safety valves for penstock inlets or energy dissipation valves for turbine bypass systems.

Apart from highly specialised valves, like plunger valves for energy dissipation or submerged discharge outlets, the company also equips entire dam projects with the complete range of valves and gates partly being manufactured through its affiliated companies Rodney Hunt and Fontaine from the US and Canada. This makes the VAG group a one-stop supplier for valves and gates including stainless steel slide gates, roller gates, Howell Bunger valves, and emergency closure valves.

VAG initiated its direct engagement in the Asian markets more than two decades ago and today runs factories in China and India. Supplies date back to the early 1950s and 1960s with several original installations still in operation. With projects under execution in China, India, Malaysia, Indonesia and other Asian countries, VAG has built up a strong name in the Asian markets as a valve supplier.

Cave hydropower station on Java
The most interesting projects are not always the biggest. One of those more challenging ones was a unique pilot project in Indonesia where VAG was involved in the world’s first cave power station on the island of Java, Indonesia.
Yogyakarta Special Province is one of the poorest areas of Java and Indonesia mainly because of the extreme lack of water. Craggy karst soil and dry seasons lasting for several months makes harvests poor and drinking water scarce. In the 1980s a cave system with underground rivers was discovered 100m below the plateau. All that was needed was a sustainable way of exploiting the source.

A German-Indonesian collaboration was established in 2000 with the goal to tap into the available water resources. The pilot project in the Gua Bribin cave was managed by Prof Dr. Franz Nestmann and Dr. Peter Oberle, project coordinator at the Institute for Water and River Basin Management at the University Of Karlsruhe in Germany (IWG).

“Over 1000 liters of water a second flow through the Gua Bribin cave even in the dry season. It’s the perfect place to build a dam," explains Oberle from IWG. The plan was to control the retained water from the cave system and collect it in an underground reservoir to make it accessible for power generation and water supply. The project would involve a VAG RIKO Plunger Valve for flow control as well as a VAG EKN Butterfly valve for isolation purposes.

However, there were many challenges to overcome as building a dam and installing equipment in the cave about 100m deep would not be an easy task. The widely ramified cave system had to be studied and measured. Care needed to be taken to protect the indigenous fauna. After thorough planning, the execution of the project would still take several years. In December 2004 the 100m long access tunnel was drilled with the vertical boring machine. The structural work on the underground dam could begin. Progress was slowed down again by events such as a catastrophic earthquake in 2006, flooding and rock fall. After several set-backs the civil works were finally completed in June 2008 and the site was ready for the valves to be installed.

The tension increased when the valves arrived at site. Getting the valves into the cave was a challenge in itself. The heavy Plunger Valve had to be lowered into the ground through the supply tunnel. Once in place the valve needed to be installed on its pedestal with limited availability of machinery and cranes. The valves were installed with an electronic actuator powered by the electricity generated by the turbines in the cave. A venting system ensures the valve operates without cavitation and vibration under any working condition.

After site works had been completed a flood test was carried out successfully at the end of June 2008 to prove that the cave and dam would withstand the pressure. The water now powers turbines that are connected by a drive to feed pumps that pump a portion of the water 200m up into a reservoir for water supply. The project was handed over to the local government in 2009 after it had been successfully commissioned. It was a pilot project and further sites are planned to be developed.

Asahan dam, Sumatra
Another exciting job was executed in 2008/09 in the northern part of Sumatra, Indonesia. On the banks of the Asahan River, the China Huadian Engineering Corporation, one of China’s largest plant manufacturers, built the Asahan hydro station within a framework of a joint venture.

For the bottom outlet of the dam there was a requirement for a free discharge valve with the high capacity of 68m³/sec at a net head at 170m. There were hardly any manufacturers who would meet this technical requirement with a single valve apart from the complex hydraulic and electric control system. With the experience of hundreds of installations globally VAG was the only manufacturer to handle such a large flow within a single valve versus other dual-valve solutions that would have considerably increased the costs for the valve, civil works, installation and operation.

Crucial aspects in the design of such types of bottom outlet valves are often issues concerning energy dissipation, wear on valve inner parts and particularly noise and vibration. Vibrations often come along with cavitation occurring inside the valve and at the valve outlet when water passes the seat with a high flow velocity. In this project flow velocities of up to 60m/sec were expected at the valve outlet which would be far beyond standard applications of a similar type. At such high flow velocities water passing the edge of the shut-off sleeve can instantly vaporise and form vapour bubbles within the fluid flow. These vapour bubbles travel along with the fluid and partly collapse within the flow or at the valve inner wall surface. They are a major cause for noise and vibration and have to be eliminated as much as possible since they can erode the material and harm the structure. Therefore an optimised design had been used and a venting device had been installed. This allows air to enter the flow before it exits the jet guidance hood and eliminates part of those vapor bubbles that would otherwise cause cavitation damages.

Another suitable valve used for bottom outlets and energy dissipation, eg in turbine bypass applications, is the VAG RIKO Plunger Valve which guides the flow towards the centre of the valve. Depending on the hydraulic conditions a suitable energy dissipation trim is tailored to dissipate sufficient energy and hinder the occurrence of vapour bubbles. With those anti-cavitation trims the flow is guided through a perforated cylinder which splits up the flow into hundreds of smaller jets. These jets meet in the centre of the valve and therefore create a hydraulic high pressure zone within the valve itself that doesn’t allow vapour bubbles to occur. VAG has executed jobs with pressure drops of up to 450mWC against only a few meters back pressure in the stilling chamber without occurrence of cavitation. This allows the use of smaller dissipation chambers and potentially reduces noise and vibration levels particularly for submerged discharge applications.

For the bottom outlet of Asahan dam with its high flow and a direct discharge to the atmosphere a KSS Hollow Jet valve was the only option. In August 2009, the huge valve arrived at the port of Belawa. Because there is neither a railway nor a highway between Belawa and Asahan, the huge crate of the size of a garage had to be transported over local roads. It took over 50 hours for the precious cargo to reach the site.

Three VAG service engineers from China and Germany were already waiting to oversee the installation works and to connect the giant valve with its actuation and control system. The heavy valve was installed quickly and skillfully with the experience of many years of site installations. The valve could successfully be commissioned and soon after was put into full operation.

These are just two examples of the many challenging projects VAG has executed over its long experience in the dams and hydropower industry in the Asian region.


Matthias Niegel, Segment Head – Dams & Hydropower, VAG Armaturen GmbH, Mannheim Germany.
Email: m.niegel @vag-group.com. www.vag-group.com