2 speed: flow rate on low is only 30% of the flow rate on hi

Diver

Well-known member
May 5, 2011
454
0
South of Boston
#1
mas985 was kind enough to estimate operating point of my superpump mated with a new 2 speed motor:

[table=2:26q3pdkz][tr:26q3pdkz][td:26q3pdkz]Operating Point[/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz][/center:26q3pdkz][/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz][/center:26q3pdkz][/td:26q3pdkz][/tr:26q3pdkz][tr:26q3pdkz][td:26q3pdkz]Pump Speed (RPM)[/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]3450[/center:26q3pdkz][/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]1725[/center:26q3pdkz][/td:26q3pdkz][/tr:26q3pdkz][tr:26q3pdkz][td:26q3pdkz]Flow Rate (GPM)[/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]58[/center:26q3pdkz][/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]29[/center:26q3pdkz][/td:26q3pdkz][/tr:26q3pdkz][tr:26q3pdkz][td:26q3pdkz]Total Head Loss (ft)[/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]38[/center:26q3pdkz][/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]9[/center:26q3pdkz][/td:26q3pdkz][/tr:26q3pdkz][tr:26q3pdkz][td:26q3pdkz]Suction Head Loss (ft)[/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]7.3[/center:26q3pdkz][/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]1.8[/center:26q3pdkz][/td:26q3pdkz][/tr:26q3pdkz][tr:26q3pdkz][td:26q3pdkz]Pre-Gauge Head Loss (ft)[/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]7.9[/center:26q3pdkz][/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]2.0[/center:26q3pdkz][/td:26q3pdkz][/tr:26q3pdkz][tr:26q3pdkz][td:26q3pdkz]Return Head Loss (ft)[/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]22.6[/center:26q3pdkz][/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]5.7[/center:26q3pdkz][/td:26q3pdkz][/tr:26q3pdkz][tr:26q3pdkz][td:26q3pdkz]Total Plumbing Curve[/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]0.0112[/center:26q3pdkz][/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]0.0112[/center:26q3pdkz][/td:26q3pdkz][/tr:26q3pdkz][tr:26q3pdkz][td:26q3pdkz][/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz][/center:26q3pdkz][/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz][/center:26q3pdkz][/td:26q3pdkz][/tr:26q3pdkz][tr:26q3pdkz][td:26q3pdkz]Energy Use (watts)[/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]1212[/center:26q3pdkz][/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]282[/center:26q3pdkz][/td:26q3pdkz][/tr:26q3pdkz][tr:26q3pdkz][td:26q3pdkz]Energy Factor (Gallons per Watt-Hr)[/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]2.87[/center:26q3pdkz][/td:26q3pdkz][td:26q3pdkz][center:26q3pdkz]6.17[/center:26q3pdkz][/td:26q3pdkz][/tr:26q3pdkz][/table:26q3pdkz]

i treated myself to white and blue 20-100 GPM flow meter and installed it today. my filter is not freshly coated and my flow was 53 GPM on high speed, which matches mas985's estimate pretty good. but on low speed the flow meter showed only about 16-17 GPM! which is about 30% instead of expected 50% of the high speed flow. i used to filter for 6 hours on high and switched to 12 hours on slow. the water is perfect, but it looks like i'm only doing 3.6 hours of filtering in high speed equivalent. so before i was doing about 0.65 turnover per day, but now on slow i'm only doing 0.4! i maintain my levels so it seems that even 0.4 turnover is enough to keep the pool sparkling! borates probably are helping too.

on recirculate, my flow rates are 66 and 26 on hi/low speed, so low speed is about 40% of high speed flow.

does anyone else have a 2 speed pump with a flow meter? are your numbers similar? i'm a little bummed out not to see 50%!
 

JasonLion

LifeTime Supporter
Platinum Supporter
TFP Expert
May 7, 2007
37,879
5
Silver Spring, MD
#2
Re: 2 speed: flow rate on low is only 30% of the flow rate o

The flow meter isn't all that precise, especially at the very low end of it's range. The accuracy of the Blue and White 300 series is +-10% of the full scale reading, which is +-10 GPM in your case. The flow rate on low will necessarily be 50% of the flow rate on high unless you have non-linear elements (typically check valves) in your plumbing.
 

jblizzle

Mod Squad
LifeTime Supporter
TFP Expert
May 19, 2010
41,193
4
Tucson, AZ
#4
Re: 2 speed: flow rate on low is only 30% of the flow rate o

Diver said:
10% of the full scale is horrible accuracy!
Yup. That is why I think having an estimate from Mark is better than spending money on the meter.

Posted with Tapatalk ... sorry if I sound short ... hate typing on phone ;)
 

Diver

Well-known member
May 5, 2011
454
0
South of Boston
#5
Re: 2 speed: flow rate on low is only 30% of the flow rate o

well, estimate is good, but i would like to know how flow rate drops are filter gets clogged. i know it's not really necessarily, but i like numbers, graphs and things like that. if you think about it majority of us here are pool geeks, so that's why i got the flow meter in first place :)
 

jblizzle

Mod Squad
LifeTime Supporter
TFP Expert
May 19, 2010
41,193
4
Tucson, AZ
#6
Re: 2 speed: flow rate on low is only 30% of the flow rate o

that actually would be interesting to see how the flow rate drops as the first pressure goes up. I assume that is how the experts here came up with the recommendation to backwash at 25% pressure rise.

Posted with Tapatalk ... sorry if I sound short ... hate typing on phone ;)
 

Diver

Well-known member
May 5, 2011
454
0
South of Boston
#8
Re: 2 speed: flow rate on low is only 30% of the flow rate o

well, for what it worth, flow rate on high matches the curve for the total head exactly. so it seems that the flow meter measures the flow on high just fine... still puzzled about the low reading on low...