Meaning of common PID diagram symbols
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Since the PID legend is not very comprehensive, many symbols are unclear as to what they mean. Generally, what is the difference between XV and XZV? Are they all cut-off valves? What does Z mean? The electromagnetic three-way valve has the markings XDY and XZY – what do they mean?
If the PID diagram is drawn in accordance with the specifications, XV refers to valves controlled by the DCS system； XZV is a valve controlled by the SIS system.
XV is a valve controlled by the DCS system； XZV is a valve controlled by the SIS system. You can check the legend
So XDY is actually controlled by DCS, while XZY is controlled by SIS, right?