New employee here: Why, when scanning the lines, does the control valve first scan the auxiliary line and then the main line?

This is a question that confuses many newcomers; I was also taught by my mentor on this. To put it simply, based on my own understanding: the bypass line is usually used for bypassing flow or adjusting small amounts of flow. By checking the bypass line first, it’s possible to determine in advance whether the pipeline is unobstructed and free of impurities, thus preventing control valve jamming or damage to the sealing surfaces when the main line is activated directly. The control valve main line is the primary flow channel; if cleaning is carried out directly, the impurities remaining inside or pressure fluctuations may impact the valve element, affecting the accuracy of regulation and even causing leaks. Switching to the auxiliary line first is equivalent to \"removing risks\" from the system; by waiting until the pressure stabilizes and the pipelines are clean before switching to the main line, the equipment can be protected. The specific procedures may vary depending on the medium and process requirements; it is recommended to refer to your organization’s operating procedures or consult experienced workers – safety first!