What sort of flow i should expect

[armstrr]

i am considering getting a flow meter to be certain what sort of flow rate i am getting. my pool has three 2" suction (main drain and 2 skimmers...all home run plumbed) and i have five 1.5" returns...again all plumbed home run. I have a 500sf pentair cartridge filter. it has a 60 psi pressure gauge on it. I increased the speed of the pump, and i could not get the needle to move off of the stop pin until i hit 1550rpm. at around 1780rpm, i can get the gauge to read 2 psi.

so, plumbing wise, i have very little resistance. any guess what sort of flow i should expect running it at 750rpm? the pentair brochure shows roughly 38gpm at around 5psi.

http://www.pentairpool.com/images/produ ... Curve1.jpg

 

[JasonLion]

I very much doubt that you will get as much as 38 gpm at 750 RPM. Something close to 20 is rather more likely, though it is impossible to say without more information.

Filter pressure gauges are not especially precise, particularly when measuring low pressures. A much more interesting number would be what the pressure reads near full speed on the pump. Even better would be the number of watts the pump draws when running at some fairly high speed.

Some other things that are good to keep in mind: variable speed pumps are most efficient at speeds very close to 1000 RPM. At higher and lower speeds you will be spending more on electricity to move the same amount of water. Also, there is essentially no point at running below the lowest speed at which your skimmer(s) work well. For most pools that is above 1000 RPM. And finally, knowing the GPM is entertaining, but not especially useful for residential pools. Nearly all of the important adjustments depend on results, not flow rate. For example the one turnover per day rule is simply a rule of thumb for guessing at what an appropriate run time might be, but most people are actually just fine with significantly less run time and the only way to find this out is to experiment.

 

[TheGoose]

I have a blue white flowmeter but I have yet to install it. It's on the "to do " list. I'm curious also.

 

[armstrr]

thanks, Jason. I'll run the pump higher and get the info you mentioned.

 

[armstrr]

Rpm watts psi
750 102 0
800 105 0
850 110 0
900 120 0
950 130 0
1000 140 0
1050 150 0
1100 155 0
1150 165 0
1200 175 0
1250 190 0
1300 210 0
1350 230 0
1400 250 0
1450 275 0
1500 300 0
1550 300 0* needle has perceptively moved off of “0 stop pin” but barely
1600 360 0.5
1650 385 1
1700 415 1.7
1750 445 2.2
1800 480 2.4
1850 520 2.6
1900 560 2.8
1950 600 3.2
2000 640 3.7
2050 685 3.9
2100 730 4.1
2150 780 4.3
2200 830 4.5
2250 890 4.8
2300 945 5.0
2350 1000 5.4
2400 1060 5.8
2450 1120 6.1
2500 1220 6.5
2550 1250 6.7
2600 1320 7.2
2650 1390 7.7
2700 1465 8.1
2750 1545 8.4
2800 1625 8.9
2850 1705 9.2
2900 1800 9.7
2950 1890 10.1
3000 1985 10.5
3050 2080 11
3100 2180 11.6
3150 2280 12
3200 2390 12.4
3250 2510 13
3300 2625 13.5
3350 2755 14
3400 2910 14.6
3450 3040 15.1

 

[mas985]

At full speed, with that setup and filter pressure, the pump operating point should be past run out so it is impossible to predict flow rates. Also I am surprised the pump isn't in cavitation.


What is the pump height relative to the water level?

How long are the suction runs?

How many suction side valves are there?

 

[armstrr]

The pump is 1' or so (maybe less) above the water level

The return lines at roughly 20', 40',60', and 80'

 

[mas985]

I was more interested in the suction side vs the return side. So.....

How long are the suction runs?

How many suction side valves are there?

 

[armstrr]

Skimmer 1: 40' skimmer 2: 60'. Main drain : 40'

All are home run plumbed to the pad inti a 2" header each with it's own 2" never lube valve.

 

[mas985]

Based on the information you gave, the pump is operating very close if not beyond the end of the head curve. This can be a problem because the pump could easily go into cavitation. When you run on high speed, is the pump making any unusual noises?

Anyway, assuming the pump is operating within normal parameters, the flow rate should be approximately RPM / 23. So at full speed, the flow rate would be around 153 GPM and at 750 RPM, it would be 33 GPM.

 

[armstrr]

the pump sounds fine. I spent yesterday hooking up plumbing to the solar panels, so that will add 100' of 2" piping plus 11 4x8' techno solis panels. I am also going to add a flow meter to optimize the flow through the panels (and for my own curiosity). i'll update this post when i have run the system with the solar and flow meter

thanks