Intelligent valves for smart control loops

With conventional centralised automation of process valves it is often difficult to meet the necessary service delivery and life cycle standards. Intelligent process valves with integrated electronic and pneumatic automation functions offer an interesting alternative in this field and can help reduce planning, installation and maintenance costs. To meet facility and water authority compliance water treatment processes must be accurate, constantly monitored and incorporate reporting outputs.

Pneumatically operated valves are currently used at numerous points in industrial and civil water treatment processes. These valves are normally automated through conventional centralised control cabinet systems, including a valve terminal, an I/O system and interfaces for communication via fieldbus.

Each individual pneumatically operated fitting in the process must be connected to the control cabinet through a control air line as well as a discrete feedback line. The costs for the planning and installation of such solutions are very high, especially on physically larger and more widespread sites.

Automation functions
In many cases, long control air lines increase the air consumption and have a negative effect on the switching times of the valves. A viable alternative to the conventional use of central control cabi nets is the integration of the required automation functions in the valves themselves. In this case, the process control system is only in charge of control and status monitoring.

At field level, pneumatically operated process valves are used, which can be equipped with all required automation compo nents such as a pilot valve with manual actuation, electrical feedback units and optical status indication, fieldbus inter faces and even positioners and process controllers.

Plants based on such decen tralised automation systems are therefore working with complete intelligent valve systems. By integrating an AS interface (ASi) as a fieldbus interface, the entire range of advantages of this approach can be fully utilised. All that is required for power supply, feedback and communica tion is a two-wire line connecting the PLC with up to 62 valves.

Each process valve is connected directly to the main compressed air supply line 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 for field deployment in demanding conditions for robust service and long life cycle. As a result, they feature the high IP protection required by the actual application and are made exclusively of weather/chemical resistant materials.

The IP protection is therefore not affected by prolonged use in envi ronments with exposure, high air humidity or by aggressive chemicals. In comparison to conventional automation solutions, this design marks a real progress as regards ruggedness.

There are further advantages to reduced electrical wiring and fewer control air lines. 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.

With conventional automation by means of control cabinet solutions, the drivers used in the plant must already be equipped with a device for electrical feed back. Innovative valve systems go a few steps further and cater for the integration of pilot valves with manual actuation, optical position indicators and other automation functions inside compact and rugged stainless steel housings.

Configuration options
Depending on the application, users can choose between different equipment and configuration options. The wide 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 displace ment transducers.

At the lower end, decentralised automation based on intelligent valve systems start with a process valve with integrated electrical feedback, simple optical feedback and integrated pilot valve. Such systems already do away with valve terminals in the control cabinets. Moving up one step in the modular valve program, users can achieve the previously described advantages of decentralised automation.

In addition to the electrical feedback and the pilot valve, these solutions include large-size super-bright colour LEDs for improved optical feedback, facil itating process monitoring at field level, and an optional AS interface serving as a fieldbus interface, with all these features integrated into the valve system.

The actuator housing is flushed with control air at each switching process as some control air is fed through at the pilot valve. This means that, upon switching, a small volume of control air is fed into the housing. This process takes less than 10 milliseconds and ensures that a slight overpressure is built up in the housing, further improving its IP protection and preventing the pene tration of humid air, for example in the event of changes in temperature or splash/submersion.

The integrated pres sure-relief valve ensures that the pressure in the housing is automatically reduced, if, after several switching processes, it reaches a value of approx. 0.5 bar. The control valves meet the same high level of ruggedness as the process valves.