The decentralised alternative: Optimised automation of hygienic processes with integrated valve systems

In the production of food and beverage, medication and cosmetics, excellent hygiene in the process and plant area plays a key role. This is enforced by states all over the world with stringent HACCP and GMP regulations aimed at protecting consumers. Companies operating in the competitive global market are however forced to make their production processes as economical as possible. As a consequence, there is an increased demand for automation solutions at process level. The conventional approach of centralised automation of process valves cannot adequately meet the ever more stringent requirements of the industry. Intelligent process valves with integrated automation functions offer a viable and efficient alternative.

In the field of process valves, conventional automation solutions including control cabinets with valve terminals, I/O systems and field bus interfaces normally require costly hose connections and wiring. With this technology, the valves at field level are connected to the central control unit through a large number of long control air lines and discrete feedback connections.  Apart from the high costs for the time-consuming planning and installation of such solutions, they are not entirely without problems as regards hygiene. An alternative to such systems is the use of intelligent process valves from the fluid technology specialist Bürkert. In contrast to control cabinet-based automation concepts, the only tasks left to the central process control system in Bürkert's decentralised solutions are control and status monitoring. At field level, pneumatically operated process valves are used. These can be equipped with all required automation components such as pilot valves with manual actuation, electrical feedback units and optical status indicators, field bus interfaces and even positioners and process controllers.

One line for up to 62 valves

By integrating an AS interface as a field bus interface, processors can take full advantage of the features decentralised automation has to offer. All that is required for power supply, feedback and communication is a two-wire line connecting the PLC with up to 62 valves. Each process valve is individually connected to the main compressed air supply line installed in the field, whereby these connections are kept as short as possible.  This reduces the number and length of hose and wire connections as well as the number of required control cabinets to a minimum. The valve systems themselves are designed according to the EHEDG guidelines for hygienic design and easy cleaning. In addition, they feature the high IP protection required for the actual application and are made exclusively of detergent-proof materials. The IP protection is therefore not affected by long-term use in ambients with high air humidity or frequent cleaning with aggressive chemicals. In comparison to conventional automation solutions, these characteristics mark real progress as regards improved hygiene.  In addition to better hygiene, less control air lines and reduced electrical wiring offer a number of other advantages. Users benefit from decentralised automation even prior to commissioning, as the approach simplifies project planning and allows for more flexible solutions thanks to 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 process valve system enables operators to monitor processes and the operating status of valves not only at a central point at control level but also directly in the plant.

Modular valve programme for tailor-made solutions

At entry level, decentralised automation based on intelligent valve systems starts with a process valve featuring integrated electrical feedback, simple optical feedback and an integrated pilot valve.  Such systems already do away with valve terminals in the control cabinets. Moving up in the modular valve programme, greater use is made of the already outlined advantages of decentralised automation. In addition to electrical feedback and the pilot valve, these solutions come with large high-performance colour LEDs for improved optical feedback, facilitating process monitoring at field level. They further include an optional AS interface serving as a field bus interface. All above features are of course integrated into the valve system. In addition, the Bürkert systems come with an analogue displacement transducer, replacing two conventional initiators or micro switches. The limit positions are thus adjusted automatically through a teach function rather than manually.

Hygienic, compact and safe

"The process valves require only minimum space and can therefore be easily installed in the pipeline system of the plant. As they are made in extremely resistant materials, they are easy to clean and provide maximum availability thanks to excellent functional safety", explains Sebastian Kundel, Segment Manager Hygienic Processing at Bürkert. The excellent availability is mainly achieved by integration of the control air supply to the actuator chambers, which ensures that the spring chamber of the pneumatic actuator is supplied only with pure and clean control air. Moisture, dust and contaminants in the ambient air can thus not enter the actuator units. This in turn effectively prevents contamination of the piston seals and corrosion of the drive springs caused by cleaning solutions entering the housing. There is also no risk of moisture from the spring chamber entering the feedback module or the control head along the spindle extension.  While this design significantly prolongs the service life of the actuator, it also enhances the hygiene of the process. As product cannot enter the spring chamber, both the spreading of germs and contamination of the inside of the actuator by mould is effectively prevented. There is thus 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 actuator design.

The control unit housing is flushed with control air at each switching process as some control air is fed through the pilot valve. This means that, upon switching, a small volume of control air enters the housing. This process takes less than 10 milliseconds. As a result, a slight overpressure is built up in the housing, further improving its IP protection and preventing the penetration of humid air, for example in the event of changes in temperature or rinsing with cold water. The integrated pressure-relief valve ensures that the pressure in the housing is automatically reduced, if it reaches a value of approx. 0.5 bar, which can be the case after several switching processes. 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. In a similar manner, digital electro-pneumatic positioners and process controllers can also be upgraded to complete control valve systems. The control valves thereby meet the same stringent hygiene standards as the process valves and come with air supply to the spring chambers as standard.

Economy and hygiene going hand in hand

"With the development of practical solutions that integrate automation functions into pneumatic actuators of process valves, decentralised automation systems have for many users become a viable alternative to control cabinet systems", emphasises Sebastian Kundel. "Food and beverage producers as well as companies in the pharmaceutical and cosmetics sector are now in a position to reconcile the commercial necessity of a high degree of automation of their production with the requirements of hygiene and safety. The modular structure of systems based on intelligent process valves ensures that they can be adapted according to the actual situation and application, whereby such optimised solutions are always based on high-quality, tried and tested components with a long service life."