Is it necessary to use long-term energized solenoid valves for non-safety interlocks?

Personally, I think process safety is also very important, and it’s best to make a choice in that regard as well.

The solenoid valves for process interlocks (connected to the DCS) don’t need to remain powered on continuously; it’s sufficient for them to be in standby mode during production ! ! ! ! ! ! ! ! ! ! ! !

Whether it’s ESD or processes, what is encountered is always long-term charging, that is, a power-loss interlock action.

I’ve heard that power-loss interlocks are rare in power plants, while both types are common in chemical processing projects. Personally, I think it’s better to design the interlocks as power-loss interlocks.

The safety interlock requirement is that, under normal conditions, the solenoid valve remains powered – in other words, it stays energized throughout the time. However, this has an impact on the lifespan of the solenoid valve, and high standards are required regarding its quality. If it’s not a safety interlock, personally, from the perspective of protecting solenoid valves, it is recommended not to use the continuously powered mode.

For solenoid valves without safety interlocks, it works like this: when power is supplied to the solenoid valve, the corresponding valve opens； When the solenoid valve loses power, the corresponding valve closes. Such a correspondence is relatively easy for everyone to understand. @jiaguoyun

Is it feasible to implement this in actual design projects? For example, if a reactor is equipped with safety interlocks and process interlocks, each using different types of solenoid valves, could this lead to some confusion and difficulties in terms of spare parts?

When I was young, I designed a pneumatic cut-off ball valve with a single-acting actuator. Considering the service life of the solenoid valve, the valve was designed to close under pneumatic pressure; the DCS program was set such that, during normal operation, the solenoid valve was not powered and the valve remained open. Only during shutdowns or in the event of fault interlocks would the solenoid valve be powered on, causing the valve to close. I was quite satisfied about it at the time. However, as people mature, they realize that this method is unsafe. Firstly, during shutdown for maintenance, when the solenoid valve is powered on, safety accidents can occur easily. Additionally, if the solenoid valve fails, it will not function properly during interlock operations in production, which can also lead to safety accidents. For this reason, a few years later, I corrected this mistake and used it as an example to warn apprentices not to make similar errors.

Thank you for sharing your experience. There is a question: for example, with a two-way three-position solenoid valve, by choosing whether the air circuit should be in the open or closed state, can it not be determined whether the valve will be closed or open when power is applied? Changing the way the valves and DCS function is a bit troublesome, right?

That would be better; you should be able to make your own judgment! Since it is a non-safety interlock, there are no safety issues regardless of how it is handled; you need to make this clear! My consideration is based on technical aspects; using the normal, uncharged version is intended to reduce unnecessary mistakes! As for spare parts and such, that’s something to consider last.