Running a centrifugal pump against a closed valve

dear,

sometimes it is required to run a centrifugal pump after starting it against a closed valve to ensure that the proper pressure is built up and then open the motorized valve.

Do we usually include a pressure transmitter before the motorized valve to ensure that proper pressure is built up and then use the measured pressure value to open the motorized valve or open the motorized valve after a predefined time?

any thought is really appreciated.

thank you!

Charbel

If it is important for the process to first allow pressure to build up, then I would indeed include the pressure transmitter.

However, no such thing as a free lunch: this also brings a new potential problem to the table that you must deal with. What if the pressure transducer is defect? Your pump would keep running and building more pressure, perhaps way too much, and thus damage things. Or worse. So in addition I would add a timer: if sufficient pressure is not detected within x seconds after starting the pump then set an error bit and stop the pump. Error bit needs to be reset before the pump can start again (i.e. operator acknowledges an on screen error message before the pump can be started again).

Zero flow in a centrifugal pump presents a risk of cavitation and eventual pump destruction. Assuming you do NOT have a check valve here, yet back flow prevention is necessary? If that's the case, you must start moving your valve to the open position the moment your pressure is equal to the head pressure of the other side of the valve. In general if that head pressure and the viscosity never changes, you could determine it empirically and use a timer, with a safety margin to cover slight variations.

Or, do what most people do when back flow must be prevented, install a check valve, then you can start opening the MOV immediately when the pump is energized. MOVs in systems where there can be no back flow is not a good solution without a check valve for the reasons Toine mentioned, but keep in mind that if the valve fails, turning the pump off does NOT solve that problem! You must always default to the valve being closed.

So if power fails, how can that happen???

I have seen this done with differential pressure across the valve in question.

When the differential pressure is within acceptable tolerance the valve is opened.

Protection for the pump is accomplished with a recycle valve to prevent cavitation. A flow meter may be required for this.