Friday, July 09, 2010

Burkert Discusses Benefits Of Integrated Valves

Decentralised automation systems have become a suitable alternative to control cabinet systems in many process sectors, according to Burkert Fluid Control Systems. This comes as more and more practical solutions are developed that integrate automation functions into the pneumatic actuators of process valves. Food and beverage producers and companies in the pharmaceutical and cosmetics sectors are now in a position to reconcile the commercial necessity of a high degree of automation in their production with the requirements of hygiene and safety.

Thanks to their modular structure, systems based on process valves can be adapted to suit many situations and applications, whereby such optimised solutions are always based on high-quality, tried-and-tested components with a long service life. In the production of food, beverages, medicines and cosmetics, the statutory requirements of Hazard Analysis and Critical Control Points (HACCP) for food processing and Good Manufacturing Practice (GMP) for Food and Drug Administration-compliant processes in the pharmaceutical industry set the most stringent standards as regards cleanliness, safety and product quality. In addition, all processes must be constantly monitored and documented.

At the same time, in an increasingly competitive global environment, companies need to make their production processes as efficient and cost effective as possible. Consequently, there is an ever-increasing demand for automation at the process level. In the field of process valves, conventional automation solutions - including control cabinets with valve terminals, input/output (I/O) systems and fieldbus connections - require extensive and costly tube connections and wiring. With this technology, the valves at field level are connected to the control unit in the control cabinet through a large number of extended pneumatic control lines and discrete feedback connections.

In many cases, long control air lines increase the air consumption and have a negative effect on the switching times of the valves. In addition, apart from the high costs for the planning and installation of such solutions, there are also concerns with regard to hygiene. According to HACCP, every additional control air and feedback line within the production plant is a potential source of contamination and risk and must, therefore, be monitored, serviced and cleaned regularly, which is a costly undertaking. The use of intelligent process valves eliminates these problems, as automation functions - pilot valves, electrical and optical position feedback and fieldbus interfaces - are integrated directly into the actuators of the process valves.

This approach, based on the principle of decentralised automation, minimises the number of cables and compressed-air lines. In addition, the concept is flexible and provides a number of further advantages. With integrated intelligent valve systems, the process control system is only in charge of centralised control and status monitoring. At field level, pneumatically operated process valves are used, which can be equipped with all the required automation components: pilot valves with manual actuation, electrical feedback and optical status indication units, fieldbus interfaces and even positioners and process controllers. Plants based on such decentralised automation systems are, therefore, working with complete intelligent valve systems.

By integrating an AS interface as a fieldbus interface, the entire range of advantages of the intelligent valve approach can be fully utilised. All that is required for power supply, feedback and communications is a two-wire connection, interfacing the PLC with up to 62 valves. Each process valve is connected directly to the main compressed-air supply line in the field, reducing the number and length of tube and cable connections, as well as the number of required control cabinets to a minimum. The valve systems are designed according to the EHEDG guidelines for hygienic design and easy cleaning; they feature the high IP protection required by the actual application and are made of detergent-proof materials.

As a result, they are not affected by prolonged use in environments with high levels of humidity or by frequent cleaning cycles with aggressive chemicals. In comparison with conventional automation solutions, the intelligent valve design delivers real progress in terms of improved hygiene. In addition, there are other advantages in respect of reduced electrical wiring and fewer control air lines. Even prior to commissioning, users benefit from the decentralised concept, as it simplifies project planning and enables more flexible solutions, thanks to the easier integration of the process and automation levels. This also applies to the subsequent installation, commissioning and maintenance.

A clearly visible status indicator integrated into the fitting allows the operator to monitor processes and the operating status of valves, not only at a central point at control level but also directly at the fitting itself. With conventional automation by means of control cabinet solutions, the drivers used in the plant must already be equipped with a device for electrical feedback. Valve systems cater for the integration of pilot valves with manual actuation, optical position indicators and other automation functions inside compact, hygienic and easy-to-clean stainless-steel housings. Depending on the application, users can choose between different equipment and configuration options.

The range of available options includes mechanical limit switches, inductive proximity switches and NAMUR initiators as well as mechanical position indicators and self-teaching limit position feedback modules with inductive linear displacement transducers. At the lower end, decentralised automation based on intelligent valve systems starts with a process valve with integrated electrical feedback, simple optical feedback and an integrated pilot valve. Such systems already eliminate valve terminals in control cabinets. Moving up one step in the modular valve programme, users can benefit from the advantages of decentralised automation.

In addition to the electrical feedback and the pilot valve, these solutions include large-size high-performance colour light-emitting diodes (LEDs) for improved optical feedback, facilitating process monitoring at field level, and an optional AS interface serving as a fieldbus interface, whereby all these features are integrated into the valve system. These systems also integrate an analogue displacement transducer, replacing two conventional initiators or micro switches. The limit position is adjusted automatically, rather than manually, through a teach function. Process valves integrating an intelligent valve design require only minimum space and can, therefore, be installed in the pipeline systems of any plant.

As they are made in resistant materials, they are simple to clean and they provide maximum availability thanks to excellent functional safety. This high level of functional safety is mainly a result of the integrated control air supply to the operator chambers, which ensures that the spring chamber of the pneumatic driver is also supplied exclusively with clean control air. Moisture, dust and contaminants in the ambient air cannot enter the drive units. This, in turn, effectively prevents the contamination of the piston seals and the corrosion of the drive springs caused by cleaning solutions entering the housing.

There is also no risk of moisture entering the feedback module or the control head along the spindle extension. While this prolongs the service life of the driver, this design also has a positive effect on the hygiene of the process. As product cannot enter the driver, both the spreading of germs and contamination of the driver by mould are prevented. There is also no risk of fungal spores produced in the spring chamber being ejected into the ambient air at each switching process, which is a common problem with conventional valves. The actuator housing is flushed with control air at each switching process, as some control air is fed through at the pilot valve.

This process takes less than 10ms and ensures that a slight overpressure is built up in the housing, further improving its IP protection and preventing the penetration of humid air, such as in the event of changes in temperature or when rinsing with cold water. An integrated pressure-relief valve ensures that the pressure in the housing is automatically reduced, if, after several switching processes, it reaches a value of approximately 0.5bar.

Through this combination of control air inlet and release, a constant overpressure is maintained inside the housing, while a certain volume of air is regularly replaced. This ensures that no condensate can build up inside the housing. Systems of the above design can be extended to complete control valve systems by combining them with digital electro-pneumatic positioners and process controllers. The control valves, therefore, meet the same stringent hygiene standards as the process valves. Provision for the ventilation of the spring chamber and the flushing of the control housing are, again, included as standard.

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