Centrifugal Fans - Instability

[zaharan]

Hi, my name is zaharan and i'm from Malaysia,
I'm having problem digesting the condition of my backward curved centrifugal fan for my grain dryer.
At full speed, the static pressure - volume flow rate curve showed a similar trend to the standard curve. However, when I reduce the speed of the fan, it behaves rather strangely.

the above is my full load curves.

this is my medium speed

this is my low fan speed

Can someone please advice me on these matters?

 

[LittleInch]

I think on your medium speed you just haven't gone to a low enough flowrate. Sharing the graph at 9380 for medium yet 8920 for full speed is incorrect. Otherwise they all show a rise at a particular flow then a drop off then a final up tick. The pressure is pretty flat for all of them.

What's the issue here?

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