Individual valves or valve terminals to control pneumatically-automated process valves? What are technical and economic advantages of these two methods? How to judge the influences with regard to commissioning? Answering this questions can result in more than 40 percent cost savings.
In the chemical industry you will find mostly individual solenoid valves for the control of pneumatically automated process valves. This kind of valves usually has a Namur interface and is direct mounted on the rotary actuator. A different way is a complete automation or system solutions which include all necessary components to control an installation from the location of the process valve up to the field bus interface. These solutions will be offered par example from Festo and include:
- Pneumatic drive with position feedback or position controller;
- Tubing and fittings;
- Air preparation (including sensors to monitor air consumption and correct operation);
- Modular valve terminal with field bus connection to superior PLC or Distributed Control Systems (DCS).
The valve terminal is the central component in this system solution. It allows decentralized automation solutions to be assembled quickly and easily. The valve terminal CPX/MPA shown in Fig. 2 is fully modular. It can control up to 64 solenoid valve coils and process digital and analogue electrical signals for communication via field bus with higher-level automation systems. It is also possible to equip the valve terminal with a PLC, which will allow installation in dedicated plant sections e.g. fermenter to be controlled independently of a DCS.
System solutions allow significant costs savings in comparison with individual-valve solutions. This applies particularly to installations with several process valves physically close to each other, for example in pharmaceutical, food and as well in chemical production. The situation could be different in the case of large installations in the petro industry, where process valves are often a long distance apart. A costs comparison will reveal the differences between valve-terminal technology and individual solenoid valve architecture.
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