21 Aug 11 11:22
Dear pro eng-tips members
There is two pumps(A/B) which one is running, and the other is spare.
Spare pump is arranged for automatic staring whenever loss of the pumping service for more than a short period of time would cause a unit shutdown.
And, it should be select the most appropriate variable that it will take a short amount of time to bring the spare pump up to speed and re-establish flow. Therefore, the point at which the spare is started should be as close to the
normal operating point as possible without causing excessive spurious starts.
It is particularly important to review the auto start setpoint versus the set point used to shut down equipment in the event the process variable is lost. There must be sufficient margin in the auto start and shutdown setpoints to allow time for the spare pump to start and re-establish the variable and to
allow for instrument drift over time.
Sorry, there is a little bit disgress.
Here the case is used a variable, flow to automatically start a spare pump. The FT-A1/FC-1 low low flow on one pump A or B autostarts other pump if available.
Unfortunately, the interlock for the pump didn't show any tag on the P&Id. I wonder that it is proper to name a tag number for this interlock or just left it blank cause there is no any information for the numbering in the cause effect table and control logic document.
Could any pro member to share what is rule in naming the interlock number ?
Thank you very much.