### Curves

2. System curve
3. Flow vs Efficiency
4. Flow vs Power consumption

Pump control by VFD: Variable Frequency Drive.
Effect of Over size pump

It is called Pump Characteristic Curve.

It means
when flow is minimum then Head is maximum &
When flow is maximum then Head is minimum.

When
Flow is increased head loss also increasing

Where Head vs flow graph and System resistance curve intersecting each other at point called pump operating point.

At this point pump is operating on most efficiently.

#### 3. Flow vs Efficiency

Initially start up time Discharge valve is in closed condition  so on this point efficiency is zero.

When discharge valve is opening gradually flow is increasing and efficiency also increasing.

After certain point power consumption is more according to flow and efficiency is reducing.

#### 4. Flow vs Power consumption

When pump discharge flow is increasing its power consumption is also increasing.

### Pump control by VFD: Variable Frequency Drive.

Pump control by VFD can Shift its duty point we can see this in graph below

We can see this...

RPM reduction 1480--> 1350
Will result into 130kW --> 65kW

Small speed reduction result into drastic reduction in power consumption.

### Effect of Over size pump

Pump is selected on basis of System characteristics curve ( head vs flow curve).

This curve is change when any valve reducer Heat exchanger NRV installed.

Example

System 1 : Green curve

Suppose we had designed system for 500m³/hr

flow for 50 meter height.

So we will choose pump with BEST EFFICIENCY POINT is near 500 m³/hr.

System 2 : Red Curve

After installation we realize that 300 m³/hr flow is sufficient.

So, we will throttling discharge valve and adding resistance to flow.

Throttling valves condition has Red Curve ( Flow vs Resistance) which has 300m³/hr flow and 70 meter height.

In actual we will operate pump at 300m³/hr and 42 meter head at point C in figure.

Conclusion

We can see Red double arrow that "Efficiency reduced from 82% to 77%"

We need pump which has Blue curve ( Flow vs Head).

Replacement of pump, VFD installation or Impeller trimming should be initiated.

See calculation