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More than 15 years with no failures
Solenoid valve technology from Festo for SIL applications for continuous operation
With more than 1500 solenoid valves of type VOFC from Festo the Bayer Division of Crop Science plays it safe in a multi-purpose system for crop protection agents – and has done so for more than 15 years. Thanks to the valves the system could statistically only fail once during a period of 2410 years due to a faulty operation.
In 2002, Bayer invested around €110 million in the construction of a multi-purpose system at its site in Dormagen near Cologne, Germany. This places everything under a single roof, from the development and manufacturing of new active ingredients for crop protection, laboratory processing, sampling and piloting, right up to the production processes.
The system is designed so that available subsystems and equipment such as dryers, centrifuges, distillers, stirrer vessels and other reactors can be flexibly connected and operated. The process control system is distributed over 67 automation systems, thus enabling the flexible adaptation of the process controls. As the process development requires the use of flammable operating fluids, frequent process changeovers and numerous interfaces and intervention points, parts of the system have been classified as potentially explosive zones 1 and zone 2 according to the explosion prevention and protection measures.
Internal and external safety
More than 1,500 solenoid valves VOFC were installed in safety-related as well as non-safety-related circuits in the multi-purpose system. A large number of these valves actuates ball valve units at tank systems, reactors or in media supply systems. Whether it is used in applications in buildings or in the open air, with large or small actuators, a universal solenoid valve is to care for all applications according to the wishes of Bayer. Last but not least, they also had to be compatible with the requirements for actuation in intrinsically safe circuits (Ex i) in zone 1.
Festo can supply solenoid valves of series VOFC and VOFD with TÜV approval (German Technical Control Board) up to SIL 3. These valves, in accordance with the latest SIL classification of TÜV Rheinland, will guarantee a failure probability rate that leads to a maximum of one faulty operation in 2,410 switching cycles. Assuming that such safety loops undergo a failsafe inspection once a year, this means that a faulty operation will occur at an amazing rate of only once in 2,410 years. These solenoid valves are available with ignition protection types “Ex em” and “Ex ia”, and are thus especially well-suited for use in safety loops.
To increase the corrosion protection, the housings of the solenoid valves are coated with Ematal so they can be used in harsh environments. To protect them against rain water and outside air, the valves have no venting holes. The exhausts have special non-return devices.
Zero-leakage compressed air supply
The compressed air supply lines for the solenoid valves, too, have been made specifically for Bayer of polyurethane plastic tubing together with NPQH push-in fittings for years. The benefit of this tubing is mainly its flexible, simple as well as time-saving installation. The tubing clip mechanism of the push-in fitting guarantees excellent tightness thanks to the integrated sealing ring, but still enables the connection to be quickly loosened when needed. Alongside the high resistance to UV radiation, the chemical resistance of the tubing was also crucial.
The plastic tubing is available in different colours, so that they are easily distinguishable for compressed air and nitrogen and need not be additionally marked. Bulk packs for longer tubing reduce the connecting fittings and therefore possible leakages.
So far none of the about 1,500 intrinsically safe solenoid valves with TÜV certification up to SIL 3 installed in the system has malfunctioned during 15 years of operation. In order to check this, Bayer removed 14 solenoid valves from the system after 15 years of continuous operation and subjected them to extensive testing in the climatic chamber at Festo. The results of these tests were extremely positive. This enabled Festo to confirm the 20 laboratory tests carried out 20 years ago with the German Technical Control Board TÜV-Rheinland.
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