Impeller Size for Pentair WF-28 w/ v-green 2.7 vs motor

[josh_j]

Last spring I changed out my Pentair WF-28 2.2 THP single speed motor with a V-Green 2.7 THP variable speed motor. Overall I have been disappointed with the flow as I have tried various speed settings and times and the suction from the new motor even when on max speed does not seem to perform as well as the original s is evident in the skimming of the pool and in the jets in the spa.

Fast forward and the screen on the v-green has taken a dump (which compounds my dissatisfaction), and while I am working through a warranty claim I am wondering if I should change out the impeller on the pump when I change out the motor from the warranty.

original Pentair motor: 2 HP x 1.1 SF = 2.2 THP
new V-Green motor: 2.7 HP x 1.0 SF = 2.7 THP
Original impeller: Pentair 073129...which I believe is for 2HP
Potential impeller: Pentair 073130 which says 2HP Full/2.5HP UP on the Inyo site

will I see performance gains from increasing the impeller size?

 

[JamesW]

Impeller......Total HP.

073126.........0.95
073127.........1.25
073128.........1.65
073129.........2.20
073130.........2.60
073131.........3.45

The 073130 is the best fit for the 2.7 hp motor and will give the best performance.

Was there water in the electrical compartment of the motor?

 

[JamesW]

To get a sense of how the performance would change, you would need to graph your system curve on the same graph as the Whisperflo pump performance curves as shown in the following document on page 9.

https://www.pentair.com/content/dam/extranet/pentair-pool/residential/manuals/pumps/whisperflo/whisperflo-pump-manual-english-spanish.pdf

Your pump performance curve will go from curve H to curve I, which does not look like much but I suspect that it will be noticeable.

Below, you can see a system curve graphed on the same graph as the pump performance curves for various pump speeds, which looks the same as various impellers.

Below, you can see how the shape of the system curve affects where the system curve intersects the pump performance curve, which defines the operating point.

Curve B represents a poorly designed system with excessive head loss due to undersized plumbing and other factors.

Curve A represents a better designed system with less restriction and is more typical.

Curve C represents a well designed system with properly designed hydraulics.

The operating point for B is 40 gpm, for A is 60 gpm and for C is 80 gpm.

So, you're getting much better flow from the same pump due to less restriction in the system or you can use a smaller pump on curve C to get the same flow as a larger pump on curve B.

https://aquamagazine.com/service/how-to-read-pump-system-curves.html

 

[josh_j]

Thanks James, I had measured TDH using pressure and vacuum gauges when the original Pentair motor was installed and when I installed the new motor and came up with 60 feet of head. With that it looks like I would gain roughly 10gpm by switching the impeller.

There was no water in the electrical compartment for the main electrical feed or the control panel, so not sure what caused the issue. It still lights up, just nothing on the display.

I did notice some corrosion on the bottom of the motor once I pulled the impeller off, but I’m going to start a new thread on that so I don’t hijack my own thread.

 

[JamesW]

Note that the head increases with more flow and decreases with less flow.

So, head loss is not a single static number.

In addition, the flow from the pump increases with decreasing head loss and the flow decreases with increasing head loss.

Each pump speed has a different performance curve for each impeller at each speed.

So, the equations are somewhat difficult because you're solving multiple equations simultaneously.

In any case, the 073130 impeller is the best fit for the motor.

You always want to use the largest impeller that the motor is rated for to get the best overall performance.

At full speed, the pump should perform exactly the same as it did before with the same impeller.

If the performance at full speed is noticeably different, then there might be another issue.

 

[josh_j]

If the performance at full speed is noticeably different, then there might be another issue.

that is what I don’t understand, with the new pump at full speed I expected the same flow at a minimum, but it is noticeably decreased at my spa returns.

 

[JamesW]

that is what I don’t understand, with the new pump at full speed I expected the same flow at a minimum, but it is noticeably decreased at my spa returns.

Is the filter clean?

 

[josh_j]

Is the filter clean?

Yes, my results were back to back comparisons between motors as well. I am just now seriously considering g impeller since the new motor is off again anyway.

 

[JamesW]

The 073130 is the best fit for the 2.7 hp motor and will give the best performance.

Not sure why the performance is currently less than before.

If you have the same impeller and the same pump speed, the flow should be the same.

Are you sure that the pump speed was 3,450 rpm?

 

[mknauss]

I did notice some corrosion on the bottom of the motor once I pulled the impeller off, but I’m going to start a new thread on that so I don’t hijack my own thread.

Keep it all here.

 

[josh_j]

Are you sure that the pump speed was 3,450 rpm?

Based on the pump controller yes. In any event I am going to upsize the impeller when I get the replacement motor in and will report back if I notice any difference.