Instrument flow diagram
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What does this valve assembly mean in the diagrams shared by marine friends?
A two-position pneumatic valve that shuts down in case of electrical or pneumatic faults, equipped with a manual switch featuring a position alarm function – it’s hard to describe all of this in just a few words.
AS indicates the direction in which the instrument air is introduced. XV-xxxx denotes the tag number of the control valve, while HS-xxxx refers to the solenoid valve on the valve body; the ‘H’ in this designation likely indicates that the valve is equipped with a handwheel. The terms ZAL and ZAH are not clear; based on their position, they seem to refer to signals related to the valve’s position, usually denoted as XZSC/XZSO. I haven’t seen this notation before, so I’m not sure what it means. Finally, FC indicates that the valve closes in case of a gas supply failure