Pneumatics at the water works pays off

"Our aim is to be the best value long-distance water supply company in Germany, offering the best quality drinking water while ensuring a reliable supply and the sustainable use of resources.” That is the guiding principle of the Landeswasserversorgung Baden-Württemberg.

Founded in 1912, the joint body provides 90 million cubic meters of drinking water every year to around 250 towns, cities and communities in Baden-Württemberg and Bavaria. Some 3 million residents are supplied through a 775 km long pipeline network, from the two water works in Langenau and Dischingen.

Danube water, provided efficiently and sustainably

The Langenau plant is one of the largest and most state-of-the-art water treatment plants in Europe. It went into operation in 1973 on the "Sptzigen Berg" on the edge of the Donauried, a river landscape around the Danube in western Bavaria between Neu-Ulm and Donauwörth. It was extended in 2014 and got a new ground water filtration system, with pneumatic automation technology from Festo.

The water, which is taken from the River Danube at Leipheim, is converted to drinking water through a multi-level process. Following three preliminary purification steps, a multi-media filtration system removes any remaining suspended particles. The subsequent activated carbon filtration eliminates organic contaminants, even in the smallest concentrations. The automation technology from Festo controls the water flow using energy-efficient pneumatically operated process valves, for shut-off and for preventing backflow.

You can read on to find out exactly what the water supply company was seeking to achieve, through the modernization of the Langenau plant. Or you can skip directly to the pneumatic solution from Festo.

Safely functioning water filters

For 100 years, the ground water from the Donauried could be used as drinking water, without needing any further treatment. Then the increasing pollution from industrial and domestic chemicals, from pesticides and from pharmaceutical residues, made it necessary to build a ground water filtration system. The special feature of this expansion was that a total of seven, two-story filter basins were constructed in an existing building. To enable this, a building that had been used for flocking and that was no longer needed, was demolished first. Resulting from this alone, there were very high requirements placed on the actuator technology. It had to be as space-saving as possible.

Regular backwashing of the ground water filter

Pure gravity is used for the ground water filtration. The water flows from the top to the bottom through a multi-media sand filter and then through an active carbon filter. While the sand holds back larger pollutant particles, the active carbon removes even the smallest contaminants.

In comparison, the cleaning of the compressed air filter is not so easy, but it is essential. The retained particles and the suspended matter block up the compressed air filter and impede the water flow. Once the filter resistance has reached a threshold of 3.5 mWS, the affected compressed air filter has to be rinsed out. To do this, the coordinated opening and closing of ten butterfly valves in the piping has to be carried out.

Compact and reliable: Pneumatic actuators

For this purpose, the water supply company went on the search for an automation solution that would handle the water flow control and that would operate in very limited space. It had to be reliable and safe and it had to include everything: The actuators and the corresponding process valves for control, for shut-off and for preventing backflow.

Up to this point, the water supply company had relied almost exclusively on butterfly valves with spindle adjustment. The spindles were operated by a handwheel or by an electric motor. But there was no space for these in the Langenau plant any more. Alongside the complex pipework, 70 automated process valves had to be installed in the space.

The solution came in the shape of pneumatic actuators from Festo. The DAPS quarter turn actuators are supplied from a central compressed air station and controlled using valve manifolds. This makes the actuator spindles and helical gear units on the process valves surplus to requirements. With this solution, the actuator is mounted directly onto the valve disc shaft.

The decision to use Festo pneumatics

An electric solution and a pneumatic solution as suggested by Festo, were up for discussion. The decision fell clearly in favor of the pneumatics. This automation solution fulfills all the requirements, and more.

Quarter turn actuators and valve manifolds

A significant part of the ground water filtration system is the pipeline valve. In Langenau, double eccentric butterfly valves are deployed both as isolation valves and as control valves. These flaps are continuously operated in alternating intermediate positions with variable opening angles. For this purpose, DAPS pneumatic quarter turn actuators are used in the Festo solution. Their swivel angle can be freely adjusted, the actuators are compact and they have torque characteristics with lever-swivel kinematics, adapted to the butterfly valves. This means that DAPS can survive even high process valve breakaway torques, unscathed.

The actuators are controlled through our CPX-VZSA valve manifold/remote I/O combination with PROFINET connection. They were installed in the center aisle, between the filter basins. A robust metal housing provides protection here in the harsh environment. The pneumatic valves themselves are completely sealed, exhaust and pilot air are captured. The CPX-VTSA records all the signals from the compressed air filters and the feedback from the actuators: Pressure, level, temperature, etc. Because the valve manifold has a highly modular design and can accept five possible valve sizes, it saves on energy as the desired flow for each valve position can be precisely adjusted.

Linear actuators and control cabinets

In addition, type DFPI pneumatic linear actuators control the side-mounted sludge water flaps, through which the retained sludge flows away from the filter in the direction of the sludge water deposit basins. A crucial feature of the DFPI is that its integrated linear potentiometer is protected from harsh environmental influences, which enhances running performance and reduces maintenance costs.

Our ready-to-install control cabinets and the complete accessories needed for the pneumatic control circuits, such as compressed air treatment, tubing and pneumatic fittings, etc, round off the pneumatic automation solution.

Long-term solution with cost advantages

All in all, our pneumatic actuator technology convinced the water supply company, because it is clearly superior to an electric actuator solution, both technically and in terms of price. With its decision for pneumatics, the water supply company is saving 10% in investment and operating costs. On account of their size alone, electric actuators would hardly have stood a chance in the cramped surroundings of the pipe cellar.

Advantages of pneumatic actuators

From the costs, through the safety aspects and on to the ease of operation, pneumatics offers clear advantages in many applications. It is an uncomplicated technology which is easy to install. Apart from end-position sensing and monitoring the compressed air supply, no check functions are required. Water supply companies benefit from this, especially in terms of process automation. Particularly when implementing complete system solutions, the cost benefits of pneumatic actuators and components over comparable electrical solutions, make a difference.

More economical than electric actuator technology

When compared to electric actuator technology, the consistent use of decentralized automation concepts with valve manifolds provides significant cost benefits – in the case of the Langenau water treatment plant, this meant clear savings of 10%. In other projects, savings of more than 50% have been possible. From this point of view, the low costs mean that it is even worthwhile automating manual process valves at a later date.

Electric actuators use a lot of energy, which they either loose as excess heat or require for the gearboxes. On the other hand, pneumatic actuators act directly on the shut-off device. Pistons and an actuator shaft are sufficient for the conversion of the linear compressed air force into a swivel motion. Pneumatic solutions only need power for the generation of compressed air and for open-loop control. Actual movement is created through the compressed air.

Durable, maintenance-free and efficient

For years, pneumatic actuators have proven to be resistant to vibration and to be durable. The reason for this is that in comparison to electric actuators, they are made from a small number of components and are thus less likely to break down. In addition, they are also resistant to continuous loads and remain maintenance-free over their entire service life. Oil changes or additional lubrication are unnecessary.

Since pneumatic actuators have overload protection and a higher actuation force can be achieved very simply by increasing the pressure, it is often possible to use smaller sizes with a lower weight. Pneumatic systems from Festo are able to deliver high forces of up to 50,000 N and torques of up to 10,000 Nm. Provided the tubing for such solutions has zero leakage and the units are precisely dimensioned, the resulting solutions are energy-efficient.

And last but not least, pneumatics is a safe solution. Because compressed air is also available in the event of a power failure. Alongside a compressor for generation and treatment purposes, an air reservoir is always available for emergencies.