4 replies to this topic

[Butterfly]

Dear all. I am dealing with a centrifugal pump with two main operating scenarios, fisrt one is pumping of 100 m3/h, and second one pumping 300 m3/h. This is flow of liquid going to storage. Flow of 300 m3/h corresponds to maximum pump flowrate, and 100 m3 is due to flowline limitations. Each scenario has a different destiny.

 

Pump minimum flowrate is 110 m3/h. I have one question regarding minimum flow valve sizing:

 

Normal/maximum valve flowrate would be 110 m3/h. What about minimum? In the second scenario (normal flow of 300 m3/h), the valve will be (or could be) closed. In first scenario, I need 10 m3/h going through the valve, so I can think of setting that value as valve minimum flow. The problem is that maybe we find out (design is not  finished yet) that I can pump, let's say 105 m3/h. Then, I could have problems with the miniflow control, cause I sized the valve for 10 m3/h minimum, and now I need 5 m3/h, valve would tend to open very litttle, and I could have pump cavitation problems. Is this reasoning correct?

 

Will I have a limitation in my design, cause I cannot pump anything between 101 and 109 m3/h. This seems weird to me, but I have to fix a value in order to size the valve.

 

So, how can I set "minimum flow of minimum flow valve"? Should I set 10 m3/h and add notes on the operating manual (do not operate between 101-109 m3/h)?

 

Thanks for your help

[Bobby Strain]

You don't necessarily need exactly 110 m3.

 

Bobby

[Butterfly]

I need anything higher than that, and a set point to determine when I need the minimum flow to open. I am using 110 m3/h for that "set point". With a different value, the reasoning would be the same, I think. If I choose 120 m3/h, and size the valve 80% open for 120 m3/h, which flowrate should I use for sizing minimum % opening of the valve?

[breizh]

Hi,

Your control valve should able to operate within the range 20 t0 80% of the max flow rate  .

"

When sizing control valves, a general rule of thumb noted in many engineering publications is to size the valve such that it operates between 20 to 80% open at maximum required flow rate. It is also recommended to have the minimum opening no less than 20% to provide a safety margin at the minimum flow rate required. "

 

Good luck

 

Breizh 

[Butterfly]

Thanks to you both