Application of Smart Valve Positioner in Chemical Plant

The control valve is the terminal of the control system, and the Smart valve positioner plays a very important role in the control performance of the entire control valve and on-site performance. The Smart valve positioner can be used in the control process of the Smart valve positioner to achieve high-quality adjustment and increase the accuracy and stability of the process control.

As the Smart valve positioner is superior to conventional valve positioners in terms of control accuracy, adaptability to the environment, commissioning, maintenance and operation costs, its practical application is becoming more and more extensive, and the problems in on-site adjustment are beginning to increase. This article introduces the structural characteristics and working principle of the Smart positioner, as well as the adjustment and troubleshooting of the Smart valve positioner.

1. The working principle of Smart valve positioner

Smart valve positioners generally adopt a modular design, with an independent module base inside, which can easily replace sub-modules on site without having to dismantle the on-site layer wires or conduits. Some sub-modules can be installed in this model field base: I/P converters, electronic and microprocessor unit components, pneumatic relays, valve position sensors, pressure indicators, etc. Some of these sub-modules are pressure indicators, etc. It is optional.

The Smart valve positioner is equipped with a highly integrated microcontroller, which uses the principle of electric balance (digital balance) instead of the traditional balance principle, and converts the input signal from the control system into a pneumatic positioning increment through a microprocessor and I/P converter.  The valve position control is realized by the signal, and the digital OPEN, STOP, and CLOSE signals are used to drive the action of the pneumatic actuator. The valve position feedback signal is directly converted into a digital signal by a high-precision position sensor and then input to the microprocessor for feedback comparison to realize the function of electricity/pneumatic conversion and precise valve positioning. The pressure sensor integrated in the Smart valve positioner is used to collect the air source pressure signal output by the valve positioner to the valve actuator, which is used to further improve the positioning accuracy of the valve and provide basis for the self-diagnosis of the Smart positioner.

2. Problems and solutions during use

In the process of adjusting and using the Smart valve positioner for several years, we have encountered some problems and failures, and summarized the following common problems:

2.1 Smart valve positioner cannot complete automatic calibration

There is a situation that the automatic calibration fails. After the manual calibration is passed, the automatic calibration is generally no problem.

2.2 Smart valve positioner cannot complete automatic and manual calibration

When the automatic and manual calibration of the smart positioner fails, the following steps should be followed to check and deal with it:

(1) Confirm that there is no problem with the gas path and that the gas path of the valve positioner is not blocked;

(2) Check whether the valve is jammed during opening and closing due to problems such as installation;

(3) Check whether the valve parameters set in the Smart positioner are correct;

(4) Improper installation position of the valve positioner feedback lever will also cause the Smart positioner to fail to complete automatic and manual calibration. Usually the lock nut on the feedback lever of the Smart positioner is loose, causing the feedback lever of the valve positioner to deviate from the original installation position. At this time, the installation position of the feedback lever needs to be readjusted.

2.3 The leakage of the regulating valve is large, the problem still exists after adjustment

If the problem still exists after the valve is automatically calibrated, the following methods can be used:

(1) For the air shut-off valve, you can first input a 20mA signal to make the valve fully closed, and then use the two lock nuts on the valve stem to adjust the valve stem, so that the valve stem moves downwards until the valve stem cannot be moved toward Move down. Then input a signal of about 12mA, and use the two lock nuts on the valve stem to adjust the valve stem to move 1/4 turn down.

(2) For the air-open valve, you can first input a 4mA signal to make the valve fully closed, and then use the two lock nuts on the valve stem to adjust the valve stem to move the valve stem downwards until the valve stem cannot be moved toward Move down. Then input a signal of about 12mA, and use the two lock nuts on the valve stem to adjust the valve stem to move 1/4 turn down.

2.4 Smart valve positioner oscillates

Smart control valve installation problem:

(1) Valve installation problems cause the valve stem to jam

The regulating valve is not installed vertically, causing the valve stem to jam, which may cause the regulating valve to oscillate.

(2) Incorrect gas connection

In the large-caliber Smart regulating valve, there is an air source amplifier before the air source of the valve positioner. Due to the insufficient air supply of the air source amplifier exhaust port during the valve movement, the valve oscillates during the adjustment process.

3 Conclusion

With the development of time and technological progress, its application will become more and more extensive. Because it has a strong self-diagnostic function, when there is a problem, it will generally give a hint of a component in the Smart locator, but sometimes these hints will mislead us, which requires us to look at the overall system To deal with the problem.