Flow meter question

fllbrent

LifeTime Supporter
May 28, 2007
5
Destin, Florida
Yesterday I cleaned the DE grids (backwashed) for the first time at new pool and the flow meter shot to over 220gpm. Before I cleaned the grids the flow meter was at zero (probably why the other pool service was let go).

The rated flow for the pool is 100gpm. The equipment is a 2 hp pump feeding 2-1/2" pipe. There are two 90's between the pump and the flow meter and the flow meter has a minimum of 3 feet of straight pipe from the last 90. I checked the meter and it is made for 2-1/2" pipe.

Is 220gpm really possible from a 2 hp motor and 2-1/2" pipe?

Thanks for any help you might be able to give.

Brent
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,082
San Rafael, CA USA
The 220 PPM is very unlikely. A 2 HP Pentair SuperFlo gets to 114 GPM at 35 feet of head (15 PSI). At 114 GPM through 2.5" pipe the head loss is around 7.2 feet of head per 100 feet of pipe with a velocity of 7.6 feet/second through the pipe. At 220 PPM in 2.5" pipe it's around 24.2 feet of head per 100 feet of pipe and a velocity of 14.7 feet/second through the pipe.

Do you have more specifics on the exact pump being used? Do you know the length of pipe from the pump to the returns? Do you know the size of the returns (diameter of eyeballs if that's what they are) and how many returns?
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,421
Pleasanton, CA
If there is any debris in the input of the meter, it will read incorrectly. You might want to pull it out and clean the end.

Also, flow meters are very sensitive to the installation and depending on the meter some require 10xD before the meter and 4xD after the meter. But what surprised me more than anything is that you have a meter which measures flow rates to 220 GPM. The larger the scale, the less accuracy it will have. What is the type/model of the meter?
 

fllbrent

LifeTime Supporter
May 28, 2007
5
Destin, Florida
Chem geek- I'm not positive about the pump, but I am pretty sure it is a Sta-rite and around seven plus years old. The length of pipe from the pump to the returns is twenty to twenty-five feet. There are seven returns (eyeballs) I do not know what size they are.


Mas985- I pulled the meter to check and see if anything was broken and it seemed fine. The meter is a Blue White F-300 series and actually measures up to 240 gpm.


I have heard about commercial pool service guys “modifying” flow meters so they can pass Health Dept inspections. I think that's what has happened here. I just really do not want to buy another flow meter and find out that the pool is really turning 220 gpm.

Thanks for helping. Brent
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,421
Pleasanton, CA
I can guarantee you that it is not 220 GPM. It is physically impossible. However, I can give you an estimate as to what your flow rate might actually be if you can tell me a few things about your pool:

Pump make/model#
Filter Pressure
Pump elevation relative to the pool surface (ft)
Suction side pipe size, length and configuration (multiple or single run to skimmers/main drain)
 

fllbrent

LifeTime Supporter
May 28, 2007
5
Destin, Florida
Thanks for the help. I replaced the flow meter today and the reading is now 120gpm. The old flow meter looked like a drill had been used on the bottom of it to widen the inlet when compared to the new meter.

Everything seems to be normal now.

Again, thank you!

Brent
 

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