Can I trust my pump?

[DrewLG]

As the first step in this season's pool project -- saving money on electricity by reducing head loss in my plumbing -- I'm plotting curves on pump charts.

My 3HP IntelliPro VSF pump reports to the EasyTouch its speed, power consumption, and flow rate. But the imprecise flow gauge in my system doesn't agree with the pump's reported flow rate, and my meter's at work so I can't confirm that the reported power consumption is accurate.

Anyone know which of those three quantities are measured directly and therefore trustworthy, and which are derived or estimated from measurements of other quantities?

 

[Jimrahbe]

Drew,

I don't think the pump has a clue what the actual flow rate is... It just assumes that if the pump is running at a specific speed what the flow rate should be..

In the big picture, it matters very little, as the cost to run an IntelliFlo 24/7, at a low rpm is way less than $20 bucks a month...

Let's see what @JamesW has to say, as he is big into graphs of pump parameters..

Thanks,

Jim R.

 

[JamesW]

Fluctuating Flow Rate

I have my ScreenLogic app set to rpm for my Intelliflo VSP. I usually have the pump rpm set to provide about 25 gpm. Over the last year the flow rate sometimes drops 1-3 gpm within a few days after setting it. Other times it doesn't change for a much longer time. When the flow drops I'll...

www.troublefreepool.com

 

[JamesW]

The pump software knows the power used for each flow at each speed.

For example, at 3,450 RPM, if the power used is 2,800 watts, the flow is calculated to be about 100 GPM.

This method is not very accurate and it can fluctuate a few GPM over time.

Document the Flow in GPM, Speed, Power and System PSI over time to see if that helps us diagnose the issue.

The System Pressure is also calculated from the power and speed.

At 3,450 RPM and 2,800 watts, the flow is calculated to be about 100 GPM and the "System Pressure" is calculated to be about 76 feet of head or about 33 psi (76/2.31).



If you have any initial conditions, you can calculate the new conditions at a different speed.

For example if the initial conditions are 100 GPM, 76 feet of head loss (33 psi), 2,800 watts and 3,450 RPM, the new conditions at 1,725 RPM are expected to be about 50 GPM, 19 feet of head loss (8.2 psi) and 350 watts.







Given any operating point, you can calculate a System Curve.

Y = (Head Loss/Flow^2)X^2

Example: 76/(100^2) = 0.0076

So, Y = 0.0076X^2.

Y is head loss in feet and X = flow in GPM.

y = 0.0076X^2, y from 0 to 80 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

y = 0.0076X^2, y from 0 to 30 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

Affinity Laws for Pumps: Principles, Formulas & Calculator

Turbo machines affinity laws can be used to calculate volume capacity, head or power consumption in centrifugal pumps when changing speed or wheel diameters.

www.engineeringtoolbox.com

 

[JamesW]

Note that the flow calculation is only valid within the specified operating range given by the grey area.

 

[DrewLG]

the cost to run an IntelliFlo 24/7, at a low rpm is way less than $20 bucks a month...

Yes, agreed. For me it's around $30/month to run at 1200 RPM, which is why I haven't done anything about it until now. But I installed an SWG last year, and to get enough flow through it I have to run the pump at 1800 RPM.

The pump-reported power consumption at that speed costs around $100/month, which is enough to get me to start thinking about ways to lower the head loss.

 

[JamesW]

But I installed an SWG last year, and to get enough flow through it I have to run the pump at a higher RPM.

You have to satisfy the SWG flow switch in any case, so this sets the lower bound for the GPM.

You can use a 1.5" T instead of 2" and this will reduce the flow required because the flow switch works on water velocity and not actual flow.

Jandy AquaPure uses a different method of detecting flow and this is not easy to adjust.

 

[JoyfulNoise]

Is your heater installed with a bypass loop in the plumbing or does all the water flow through the heater? There is a significant Amount of head loss from the heater even though the manifold is designed as a high-bypass flow. Bypassing the heater completely when not needed can significantly reduce head loss. Some people have quoted as seeing as much as a 30% increase in flow rate when a bypass is used. Might help with your situation. However, if you did install a bypass you’d either need to automate it or you would need to replace the pressure switch on the heater with a flow switch to ensure that the heater can’t fire up without the bypass closed enough to give adequate flow.

 

[JamesW]

Given any operating point, you can calculate a Power/Watts Curve.

Y = (Power/Flow^3)X^3

Example: 2800/(100^3) = 0.0028

So, Y = 0.0028X^3.

Y is Power in Watts and X = flow in GPM.

 

[JoyfulNoise]

If you want to know your system head loss and flow rate, you can try to measure the pressure differential across the pump by putting a vacuum gauge on the strainer pot drain port and a pressure gauge on the pump discharge drain port. You can also use the pressure at the filter gauge too if you trust it. The pressure difference is related to flow and total head … I’m sure @JamesW can whip up a nice Mathematica plot for that.

 

[JamesW]

I’m sure @JamesW can whip up a nice Mathematica plot for that.

I just ask Google Gemini, Microsoft Copilot, ChatGPT and Claude what the answer is and they tell me everything.

If they disagree, I just say “Well, that’s not what the other chatbots say” and then I let them fight it out.

Right now, Chat GPT and Claude are arguing about the correct answer to this thread and I will post their answer if they can agree.

 

[JoyfulNoise]

I just ask Google Gemini, Microsoft Copilot, ChatGPT and Claude what the answer is and they tell me everything.

If they disagree, I just say “Well, that’s not what the other chatbots say” and then I let them fight it out.

Right now, Chat GPT and Claude are arguing about the correct answer to this thread and I will post their answer if they can agree.

 

[JoyfulNoise]

The original toy was made out of sheet metal for the base with sharp rusty edges and the robots were cast from a plastic material high in formaldehyde residues … and there was no Prop 65 warning back in the good old days. If you sliced a finger on the side of the game then you just went to the hospital and took your tetanus shot like a man!! It was a right of passage. And the formaldehyde only causes cancer if you live too long anyways.

Bunch of sissies nowadays …

 

[JamesW]

If you sliced a finger on the side of the game then you just went to the hospital and took your tetanus shot like a man!!

We just had Robitussin for things like that.

 

[DrewLG]

Thanks, guys. @JoyfulNoise I do not yet have an external heater bypass, but I think I'm going to install one. My EasyTouch seems able to operate a diverter valve when the heater turns on, but I guess I should test and confirm that before I spend the money on a valve and actuator.