How to add a DCS control to a cylinder valve of the type controlled by two solenoids?
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The cylinder valves of the two solenoids are those commonly used in interlocking applications; are two DO points required? One valve to open and one to close? If that’s the case, when I open the valve and then close it again, how does the solenoid valve that controls opening the valve lose power?
No image – it’s the type of cylinder valve commonly used in SIS, with two cylinder valves stacked on top of each other; it’s controlled by two solenoid valves
One-point control, with the on-site actuator inverted
Since it is used on the SIS, thorough consideration was given, and two solenoid valves are used. But there are two scenarios: if the concern is accidental operation, then the two solenoids operate in series, which means that both solenoids must lose power or gain power for the valve to move. If the concern is rejection of the operation, then two solenoids operate in parallel; the signal from the SIS indicates that both solenoids should be de-energized or energized. As long as one solenoid is operating, the interlock function is activated. So the client needs to see what type of connection the solenoid valves actually use.
I see that the air circuits of the two solenoids are connected in series
The statement on the 6th floor is incorrect. Under normal circumstances, it’s a power-loss interlock mechanism in place to prevent accidental operation; therefore, two solenoid valves operate in parallel, and the valve will only move when both solenoid valves lose power； To ensure safety, the two solenoid valves operate in series; if one of them loses power, the valve will close
Refer to Clause 7.4.5 of the explanatory notes for GB/T 50770-2013 \"Code for Design of Safety Instrumented Systems in Petrochemical Industries\" for the instructions on the redundant configuration of solenoid valves, as well as the wiring diagrams; everything is explained clearly there.
It’s interlocked with the SIS system; one needs to check the pneumatic circuit diagram to see what type of connection is used. Generally, two DO points are required!