Valve interlock issue

The situation you mentioned generally refers to the typical logic of the valve interlock circuits in a Safety Instrumented System (SIS). Here is a brief explanation: 1. Regarding the signal you mentioned: – 381UZ-005 is usually a shutdown signal coming from some upstream safety interlock (such as an emergency stop, high pressure alarm, or other abnormal process conditions) (automatic interlock). - 381HS-0003 generally refers to a hand switch used on-site; it is employed to send a signal to close the valve manually during on-site operations. It is usually installed in the control room or on the on-site control panel, serving as a means for manual intervention. 2. The operation process is roughly as follows: – Under normal conditions, this isolation valve can be switched on and off remotely, manually, or on-site. - When process parameters deviate to the interlock set values (such as excessive upstream pressure, equipment failure, or emergency shutdown), an automatic interlock signal (here 381UZ-005) is sent to issue a command to close the shut-off valve, causing it to close automatically. - If the process requires human intervention (in emergency situations or for other reasons, by operating the manual button 381HS-0003), the valve can also be manually forced to close. 3. Meaning of “2 out of 3 valve position selection for interlock removal”: – The so-called 2 out of 3 valve position selection (also known as 2oo3) is a redundant design approach commonly used in safety interlock systems. It involves using three independent valve position feedback signals (or valve position switches) to determine whether the valve is actually in the correct position (such as fully open or fully closed). Only when at least two of these signals indicate that the valve has indeed reached the predetermined safe position will the interlock system consider the valve to have functioned correctly, and thus confirm that the interlock action is valid. - In simple terms, three sets of valve position feedback signals are defined; the interlock logic will actually be activated only if at least two of these three signals meet the interlock conditions simultaneously. To summarize: - 381UZ-005 is the valve-shutting signal from the automatic safety interlock ； - 381HS-0003 is the manual valve closure signal ； - “The “3-out-of-2” (2oo3) logic is a safety interlock design implemented to ensure reliable valve operation and prevent incorrect interpretations of a single signal. .

Thank you for your reply. What does valve position interlock mean here?

The term “valve position interlock” here means that the interlock logic requires not only an instruction to close the valve (such as the 381UZ-005 automatic interlock signal or the 381HS-0003 manual switch), but also confirmation of the actual position of the valve itself (such as a feedback switch indicating whether it is fully open or fully closed). Only after the valve actually moves to the specified position (for example, when it is confirmed that the valve is fully closed) is such an interlock action considered valid and meets the interlock logic requirements, thereby allowing subsequent safety protection actions to be carried out. In other words: 1. The interlock signal issues a command (automatically or manually) to close the valve. 2. After the valve actuator moves, a valve position feedback switch is used to determine whether the valve has actually closed properly (for example, if three valve position feedback signals are available, a \"two-out-of-three\" logic is applied to confirm the valve position). 3. Only when the valve position meets the confirmation criteria (that is, at least two out of the three valve position signals confirm that the valves have been fully closed) will the DCS or Safety Instrumented System (SIS) consider the valves to be successfully closed, thereby completing the entire valve position interlock logic. In short, \"valve position interlock\" is a mechanism in the control logic used to verify the actual position of the valve, ensuring that its true state meets the requirements of the interlock design and confirming whether the valve has moved to the safe position as intended, rather than simply sending a shutdown signal and ending there. .

The three analog values 381UZS0011A/B/C are compared with the target value you have set; if any two of these analog values are greater than or less than the set value, it triggers the three-way valve 381UYX0011 to change the flow direction of the fluid, thereby keeping valve 381UV0011 in its safety position.

This post was last edited by chenzx on 2025-7-18 10:10. Thank you, I roughly understand it now – it’s to prevent the valve position from being too high or too low, right? If the design value is reached, the solenoid valve activates, and then the valve position remains unchanged. But does this valve appear to be manual? It’s not obvious that it’s automatic; then why is this needed to prevent the valve position from being too high or too low?

381UV0011 is a cut-off valve; three limit switch signals are used to determine whether the valve has been opened or closed fully. After an interlock action occurs, the system must receive a feedback signal (from the limit switches) in order to assess whether the interlock action was carried out successfully, thereby ensuring safety.