Considering a VS motor? Look at the whole system to optimize performance.

[JamesW]

For most people, knowing the system curve is not that important other than if you just like doing that sort of thing.

You can usually just adjust the flow until it does whatever you need it to do.

 

[setsailsoon]

If you use my spreadsheet, you only need to use the filter pressure and a description of the suction side plumbing (PSI2GPM tab).

Thanks! This help a LOT and I need all the help I can get. It's usually me against the entire dinner crowd!

 

[jonpcar]

Thanks! This help a LOT and I need all the help I can get. It's usually me against the entire dinner crowd!

Chris, I was traveling during this period and missed this conversation entirely, but found this thread with some searching for ideas.

I am getting very close to starting my own experiments to establish my system curve...yeah I know it’s nerdy but I just want to know all the data about my system. Did you follow up on this and go through with the measurements necessary to develop your system’s curve? What data did you (or are planning) to take? I’ve really appreciated looking at @mas985 pump spreadsheets but want the data specifically for my system. It also helps me get my head around understanding it better by going through a process.

My plan (probably still about a month away) is to take data that will include varying my VS Pump RPM over a range of system conditions, from my system’s highest head condition to its lowest head condition. TBD, how many stages in between these two extremes, and how many RPMs at each stage. It will depend on how automatic the collection of data can be.

From previous experiments, I believe that these are the two extremes for my system:
(1) IFCS On: highest pressure, most restrictive, highest head condition
(2) 100% Wall Returns: lowest pressure, least restrictive, lowest head conditions

TBD on data collection for how the suction sources impact this: main drain versus skimmers. It will depend on how much these impact the results. It may be that one of these (probably main drain) folds into condition (1) above, and skimmer draw folds into (2) above.

At each data point I will take the following data:
1) RPM
2) PSI (pump vacuum side)
3) PSI (pump filter side)
4) GPM (via FlowVis), must be manually entered
5) pump watts

And then I will process the data...my goals include:
1) developing an accurate, dynamic GPM model for my system
2) next, remove my FlowVis to measure how it impacts (impacted) GPM/efficiency
3) understand better how dynamic changes in system head (via dirty filter, debris baskets full, IFCS) impact my system
4) use the information to help determine if there are better pump RPMs to do what I am doing, but more optimized/efficient
5) having some fun

Are these realistic goals and am I missing something obvious that will NOT allow me to accomplish them?

 

[setsailsoon]

Sounds like a neat fluid mechanics lab exercise that will help set optimum speed settings. @JamesW and @mas985 should have a blast with this!

 

[mas985]

Keep in mind that the accuracy of pressure gauges and flow gauges are not very good at the low end of the scale so the percent error will grow with lower RPM. I find it much more accurate to calculate the operating point at high RPM and then use the affinity equations for lower RPM. This is what the spreadsheets do for you. It determines the plumbing curve from the highest RPM measurements and then estimates the flow rate, head and pump power at lower RPMs.

However you won't see much of an impact for a single check valve.

 

[jonpcar]

Keep in mind that the accuracy of pressure gauges and flow gauges are not very good at the low end of the scale so the percent error will grow with lower RPM. I find it much more accurate to calculate the operating point at high RPM and then use the affinity equations for lower RPM. This is what the spreadsheets do for you. It determines the plumbing curve from the highest RPM measurements and then estimates the flow rate, head and pump power at lower RPMs.

However you won't see much of an impact for a single check valve.

Mark, thanks...I’ll keep that in mind. I will do both the high RPMs and the low ones. When I do it, I will post the results to see if they are meaningful or not. I have installed some used industrial electronic PSI gauges in my system (-14.7 to 50 psi) and they seem to be very accurate although I don’t know how they are on the low scale since I can’t really compare them to my analog gauges at those lower RPMs. I read the gauges upto 50 times a second and average the results...the FlowVis will be tough at the very low end.

I’ve been wanting to take out that FlowVis for awhile...especially since it is in the intake line to the pump. I won’t remove the valve housing, just the insides to make it a feedthrough. You are probably correct about not seeing any impact...but I was particularly concerned about that check valve when I was running at high rpm. I still want to know gpm numbers so I’ve procrastinated until I hopefully have a semi-accurate dynamic gpm calculation method to replace the FlowVis

 

[cfherrman]

If your using a gauge get one with a air bleed

 

[jonpcar]

If your using a gauge get one with a air bleed

No bleeder on these but they are mounted horizontally...on my pump (2), filter, and IFCS head. I paid $17 each on eBay, so ignore the price, haha. These have given me absolutely no problems in the 12 months they have been installed...more consistent than I could have imagined. So far I have just “looked” at the data because I’m still making other software/hardware changes to my system.

Setra Systems Inc. - 2091050PC2M2402 - Pressure Transducer; -14.7-50 PSIG; 1/4" NPT Male; 0.5-5.5 VDC; 2 Foot Cable - Allied Electronics & Automation

2091050PC2M2402 from Setra Systems Inc. at Allied Electronics & Automation

www.alliedelec.com

 

[cfherrman]

Consistent sure, accurate not without a air bleed

 

[jonpcar]

Consistent sure, accurate not without a air bleed

Hey Casey...so in your opinion, a pressure gauge has to have an air bleed valve to be accurate, can you explain? Also, if you were going to do these “experiments,” do you have an example of what gauge (with bleeder) that you would recommend? Thanks.

 

[cfherrman]

A low pressure gauge with fluid in it has the air pressure from the factory in the case, which is a different air pressure where you are at, and the air pressure changes over the seasons. A air bleed will zero out the case pressure and the gauge will move 1-2 psi. You only see these on 30psi or less fluid filled gauges (and in my applications it's a vac/pressure gauge), gauges over 30 psi 1-2 psi being off doesn't matter.

I don't have a brand preference

 

[jonpcar]

Casey, thanks! I think I understand...so the concern is the initial air pressure on the “inside” of the gauge, which is set in the factory and will be dependent on all the factors you mention, and that won’t necessarily match the conditions where the gauge will be in use.

But, isn’t that what is compensated for through calibration, the most important calibration being simply a “zero offset” (seems to be effectively a “bleed”)? My four gauges have slightly different offsets to ensure that “0 PSI” is read when the pump is off. This method ignores reading “absolute PSI readings” which would reflect the altitude here in Gilbert, but knowing “absolute PSIs” is probably a “don’t care” for this application.

I hope I am thinking correctly on this...thanks again!

 

[cfherrman]

I would think(but don't know) it would be off as the spring inside the case gets compressed, it will compress at different rates at different case pressures. Now, does this matter enough, probably not but as one who loves super precision, it would to me.