Differences in the operating states of valves (LO, LC, NO, NC)
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This post was last edited by qq375170364 on 2009-9-2 at 15:43. On a typical PID diagram, valves have the following states: LC – locked in the closed position; LO – locked in the open position; NC – normally closed; NO – normally open. What is the difference between LC and NC, and between LO and NO? Please explain, experts.
LC stands for LOCKED CLOSED, while NC means NORMALLY CLOSED; the choice depends mainly on the requirements of the manufacturing process.
The valve is locked to prevent accidental operation
To some extent, valves that open and close are critical areas where operational errors are not allowed. For example, in certain safety valve assemblies, there is a specific sequence and logical order to operating the valves during pressure testing, and this can be fully achieved through valve locks to prevent accidental operations. Moreover, it is not necessary to be on-site; the opening and closing status of these valves at the site can be determined using the keys left on the special key box provided by the valve lock manufacturer, and it is even possible to connect to the DCS system. On the other hand, normally open and normally closed valves do not have these special requirements.
There are also F.C and F.O, which stand for Fault Off and Fault On.
NO = NORMAL OPEN, which means it is usually open, but can be closed under certain conditions; whereas LO cannot be closed. In other words, valves of the LO type are generally not installed in those locations – they are installed only when it is necessary. The difference between NC and LC can be inferred in a similar manner.
LC means locked in the closed state, and this state does not allow it to be opened; NC (normally closed) means it is closed under normal conditions, but may open under special circumstances; LO means locked in the open state, meaning that the valve cannot be closed, and local valves are generally not installed on either side of it; NO is a normally open valve, but it may close under special situations.
I learned a bit about it; I’ve been researching PID charts lately
The answer on floor 8 was complete and accurate. top
It is said on the 7th floor that LO was installed as a last resort – what exactly does that mean? For maintenance?