If it needs an SOP to be safe, it needs an interlock

Spent my morning digging through HMI fault logs again. Another pump seal roasted because the unit started with the discharge closed and the seal flush blocked in. Well, there’s your problem. I keep hearing that we’ll train the operators and update the SOP. My answer is the same as always: just interlock it.

We added simple permissives: no start unless discharge valve proof open, seal flush pressure proven, suction strainer DP below limit, and the VFD will not ramp if NPSHa proxy is low. Trips latch on high vibration or low seal pot level. None of this is fancy. It just enforces physics.

Result: alarm noise dropped, seal life improved, and nights got quieter. Yes, too many interlocks can make a plant brittle, but nuisance alarms and cooked equipment are worse. If it takes a paragraph in an SOP to explain a safe start, that logic belongs in the PLC.

Where do you draw the line between operator judgment and hard interlocks? What single permissive or trip has saved you the most downtime?