Getting a better turn over rate

[Ecozadd]

I would like to see how many gallons per minute (gpm) I can get out of my 2 HP pump (2 inch line) and 140 gpm rated filter. In normal operation I tend to max out at 80 gpm, however when I "backwash" or "rinse" I get about 120 gpm flowing though the plumbing. Not sure why normal operation lowers the gpm to 80.

My first thought is that the sand is calcified, but wouldn't that slow down the "rinse" operation also? I regularly break up my sand to keep it loose. So i think i have ruled this out.

My second thought is that there may be an obstruction in one or more of the three return lines, although i don't have a good way of checking them. If you have a good way of seeing if the plumbing is clear let me know.

A third possibility is that the attached heater may obstructing the flow. There is no by-pass which is something i am looking at correcting.

Any ideas on other possible scenarios or if 80 gpm is going to be my best flow rate? What i have read is that a 2 inch inlet could potentially yield a 200 gpm flow (probably not with a 2 hp motor though).

Pool Info: Indoor commercial 180,000 gallon pool. Three total filters with two heaters. Sand is Zeolight brand very old (5 or more years).

[PoolDoc]

Eco;

I'm sorry, but we treat commercial pool questions at a lower priority than other questions, for reasons I've explained in other posts in this section.

I'll ask mas985 if he wants to take a look, but like I said, it's not a priority.

I will offer this: I've worked with Pentair / PacFac TR-140's many times, with various optimizations. On a 36" filter, with 2" piping, 100GPM is the usually upper PRACTICAL limit. More than that, and flow losses are very high, PLUS filtration quality deteriorates. You're getting much better filtration at 80 GPM than you would at 140 GPM!

For 6 hour turn-over, your pool needs FIVE or SIX 36" sand filters, fed off of, and discharging into, 6" or 8" header piping. If you've got the typical home-pool-builder 2" PVC spaghetti . . . well, you've got a mess.

If you want professional help, come September, I can probably work with you, but at rates over $100/hr.

Two more things:

1. If you are doing this for code compliance, 140 GPM is NOT the commercial rate for those filters, and if your inspector is on the ball, he won't accept flow achieved that way.

2. If you are seeking better water quality, well you won't get THAT, either for the reasons mentioned earlier.

[mas985]

I would like to see how many gallons per minute (gpm) I can get out of my 2 HP pump (2 inch line) and 140 gpm rated filter. In normal operation I tend to max out at 80 gpm, however when I "backwash" or "rinse" I get about 120 gpm flowing though the plumbing. Not sure why normal operation lowers the gpm to 80.

This is normal and it is because there is a lot more head loss in normal operation than there is in backwash operation. When in backwash, the water no longer travels through the return pipe, fittings, eyeballs and heater which all add head loss.

But to see if 80 GPM is reasonable for your setup, I would need to know a lot more detail:

Suction pipe diameter (e.g. 1.5", 2", 2.5")
Average length of suction pipes
Number of individual suction pipes from the pool to the equipment
Number and type of suction side valves
Current Pump Make/Model
Height of pump relative to the water level
Pipe size between pump and filter (e.g. 1.5", 2", 2.5")
Filter type, size and multi-port valve size
Filter PSI reading at the desired valve settings and pump's highest speed setting
Height of pressure gauge relative to the pump center line
Heater - yes or no
Number and type of return side valves
Return pipe diameter (e.g. 1.5", 2", 2.5")
Average length of return pipes
Number of individual return pipes from the equipment to the pool
Number of return eyeballs (usually more than the number of pipes)
Return eyeball inner diameter (e.g. 1", 3/4", 1/2")

[Ecozadd]

Thank you Pool Doc & mas985,

I'm thinking that the 80-85 gpm I currently get is probably the best i can do. You are right that we have a mess of piping and products installed that is probably not going to cut it for a commercial industry pool for very long. It is now up to me to sort out a way of getting the pool re-plumbed and done by commercial pool pros this time around.

Great forum and i'll be back soon with more questions.