Problems with instrument control valves
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On one of the design drawings, it can be seen that many of the pipelines for instrument control valves lack bypass lines, and these control valves have only a front cut-off mechanism without a rear one. Liquid ammonia flows through the pipeline. Excuse me, expert – what is the principle behind this? Common control valves all have auxiliary lines as well as mechanisms for switching between front and back operation.
The bypass line is set only as needed; the presence of valves before or after the valve does not necessarily mean they are intended for use with control valves, and they can also be used in emergency situations
In the past, most control valves came equipped with bypass lines; nowadays, most of the control valves in newly designed devices do not have such lines, with bypass lines being provided only for those that are particularly important. This concept is constantly evolving.
In the past, the regulating valves did not perform well, requiring frequent on-line repairs. To ensure the normal operation of the process, a bypass line was designed to facilitate repairs to the regulating valves. The quality of control valves is continuously improving, so the use of bypass lines is gradually being reduced. That’s how I understand it.
In other words, this change is not based on any specific standards or working principles; it is simply a result of rational resource conservation (due to the improved quality of the valves)
May I ask, 1: Can “it depends on the requirements” be understood as meaning that as long as the control valve is of good quality, I don’t need a bypass line at all? 2. Is the secondary line a mandatory design requirement?
No matter how good the quality of the valves is or how advanced the technology, I still think a bypass system is necessary for equipment; after all, every piece of equipment will eventually fail. The purpose of a bypass system is to facilitate maintenance work
A backup line should be added; even the best valves can fail at times