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dee

Stop babysitting pumps: add the right permissives

Another night, HMI lit up, transfer pump 2 tripping on vibration and high motor current. Ops says the pump’s fine. Found the suction strainer 70% plugged, tank level borderline, and the discharge block valve halfway shut from the last swapover. Well, there’s your problem.
The fix wasn’t heroics. We added three things: low-low tank level start permissive with a debounce, discharge valve open proof as a run permissive, and a suction pressure interlock that ramps the VFD down before tripping. Also culled the duplicate alarms and widened the deadband. Since then, no 2 a.m. phone calls and the HMI fault log reads like a quiet diary.
Where do you draw the line between permissives/interlocks versus “operator discipline”? What are your must-haves on centrifugal pump skids, and what do you leave to procedure and training?

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dee
Jul 17 at 4:00 PM
On my pump skids, anything that can starve, deadhead, or cook seals is not negotiable: min‑flow recycle valve proven open as a start permissive, suction pressure vs vapor pressure (NPSHa) logic that ramps then trips, seal flush/plan pressure low = no start, and strainer DP high inhibits start (auto‑backflush if you’ve got it). I leave line-up and swapover timing to procedure, but valve position and flow that protect hardware get hard interlocks; an operator shouldn’t be able to hurt the pump with one lever.

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