Pump/Motor Sizing

[CrimsnTide]

Someone want to take a crack at this?

Our NEW pool has had water in it for ONLY TWO weeks now. I am now wondering if the PB calcualted the right size pump. My question arises due to I am not sure if the skimmers are working as well as they should

If my sig doesn't have all the info, I hope the following does

16x50 In Ground Pool @ 34,000 gals
Rectangular in shape 4' to 8' deep
Plaster w/SWCG (not operating yet)
2 Skimmers one at end of pool, one on side in middle
NO SPA or WATER FEATURES - NONE

Jandy Stealth High Head Full Rated 230/115 VAC .75 HP Pump
Jandy 460 sq. ft. Cartridge Filter
Jandy 400,000 BTU High Efficiency Gas Heater

Two "drains" are connected to each skimmer. Each Skimmer seperately plumbed with 2.5 pipe (as far as I can tell)

From going to a a few websites, they all ask pretty much the same thing for calculations:

Size of Pool (Gal.): Approx 34,000
Gallons per Hour (GPH): 4,250
Gallons per Minute (GPM): 70
Approx "Feet of Head" : 60

At first, just a visual into the skimmers, I didn't think they were really doing what they were supposed to to. We played with the "door flapper" to get possibly a "equal" pull from both the skimmer and the drain. I'm not sure if this is being done. There is NO valve to switch up at equipment. I have the ability to shut down one skimmer (and Drain) or the other one in the same fashion.

I don't think the pump is actually big enough.

When the pump/motor turn on, does one expect the FULL capacity of the pool to go through the filter? Our pump is set to run about 4.5 hours daily.....

Any care to do my math over again? Is there any other information I can provide?

Again, simple pool. But it is large.

Thanks.

 

[JasonLion]

That pump is more than large enough for normal day to day circulation. It is probably a little small for cleaning up a major algae bloom, but that should be a rare occurrence, and it isn't way off, just a little.

How well the skimmers skim has more to do with the water depth and how well the return jets are aimed to create an appropriate circulation pattern. You should see debris moving is a circular pattern and carrying debris to the skimmers (unless the wind is high). Once the debris is quite close to the skimmer it should be drawn in. Skimmer efficiency also depends on the wier door blocking all but a shallow surface layer of water.

 

[CrimsnTide]

Jason,

Thanks for the reply... I would think that the pump would be strong enough, but my wife and I are questioning it. By just looking at the skimmers work, we will see small debris float right on by with hardly any resistance from the skimmers. And with both the skimmers on, I've seen leaves actually return to the pool from the skimmer. Now looking at the graph below(from JANDY/Zodiac) and with a flow of approx 70 GPM and 60 Feet of Head, it appears maybe we should have been moved up a size? I am also wondering if it's TOO late to consider a variable speed? Again, pool has only had water in it for two weeks.

Are my numbers off to not worry about this????

 

[jblizzle]

Do your skimmers have weir doors?

Head loss is a function of flow rate and not trivial to calculate ... you can not have a 70GPM and 60 ft of head because that is not on the line of your pump.

I only have 40-50GPM of flow and thing are fine.

 

[duraleigh]

Depth of your pool water (1/2 way up the throat of the skimmer) and the correct functioning of the weir door is about hundred times more important than the pump size. Do you have a main drain and can you divert water from it to the skimmers?

 

[JasonLion]

From your description there might be something wrong, but it doesn't have anything to do with the pump being too small.

How is your return jet pressure? And what is the pressure reading on the gauge on the filter?