An air separation equipment has 21 control valves for 24-hour gas supply. After running the device for a period of time, the customer reported that some of the control valves on site had no valve position feedback. When encountering abnormal valve action, it was difficult to detect it in time. The valve control performance is poor, and the actual valve position deviates significantly from the control signal, which caused the device to trip. The customer urgently needs a solution.

The control valve, actuator, and mechanical controller of the device are all non-Fisher brand, and the overall budget is limited. Based on SWD and discussions with the customer, the SC engineer provided a plan: replacing the old mechanical pneumatic controller with Fisher's and adding Fisher 4400 position feedback. With years of good cooperation and SC's professional capabilities, the client adopted our suggestions.

Fisher 4400 is a newly launched product. A Fisher FIELDVUE 4400 digital position transmitter senses the position of rotary or sliding-stem valves, vents, dampers, or other devices. It provides a precise non-contact feedback to indicate equipment position with a percent (%) of span plus on/off indication. The 4400 provides 4-20 mA position feedback, is SIL 2 capable, and has two 1-amp NAMUR design solid-state limit switches. 

In addition to basic valve position detection and transmission functions, Fisher 4400 position feedback can also provide diagnostic functions for valve action time and dwell time.

The typical application scenarios of Fisher 4400 position feedback are as follows:
1. The application of high-frequency switches often leads to wear and detachment of mechanical valve position connections. For example, PSA and frequently operated inlet and outlet valves;
2. The electric actuator valve position sensor is located inside the electric head and cannot accurately measure the valve position. 4400 can be directly installed on the valve stem;
3. Key hazardous areas, such as critical valves in nuclear power plants, require the addition of valve feedback information;
4. Other applications that require measurement of position movement, such as safety valve action measurement, air damper baffle, etc; 
5. SIS application requires independent valve position feedback measurement that meets SIL level requirements;
6. Application scenarios that require simultaneous provision of 4-20mA and valve position on/off measurement.

After some testing by the SC engineers, the final plan was successfully implemented. All key valves have real-time valve position feedback that can be monitored.

In order to further improve the reliability of the overall device, the SC engineer replaced all four valves and actuators at critical positions with Fisher valves and actuators. Two of them used Fisher DVC6200 digital valve controller, and the other two used Fisher mechanical pneumatic controller + Fisher 4400 position feedback.

After the improvement, the factory encountered an emergency situation of power failure caused by typhoon and rainstorm. The standby unit was switched smoothly, and all the reformed equipment was put into normal use, which reduced the losses caused by natural disasters. The customer was very satisfied. In an internal meeting, the transformation plan was shared and will be implemented to similar application conditions.

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