Please check my filter and pump calculations

[BuckeyeFanInFL]

I thank everyone for your responses to my posts below. I have researched flow rates, pumps and volume. Here is what I have come up with:

I have a 10,000 in ground pool. I want the pump to turn over the pool in 8 hours. So, 10,000gallons / 8 hours = 1250 gallons per hour. 60 minutes in the hour so, 1250 gallons / 60 minutes = 20.8 gpm. So I would need atleast a 21 gpm pump. There is approximatly 20' between my pool suction and the pump suction, so I will need to check the pump curve at 20' of head.

The sand filter that I have is a Jacuzzi Laser L190, 19" and can handle a maximum of 37gpm per minute. So the filter would be more than adequate???

And just as an example, I see that WhisperFlo has a pump curve for the various sizes at http://www.recreonics.com/whisperflo_pump_curve.htm
The 1/2hp pump at 20' of head can pump 90 gpm. Did I do all the steps correctly? Would that pump still be over sized for the filter, by providing to much gpm??

[JohnT]

Head is not horizontal distance. Head is roughly defined as "resistance to flow". Most commonly it is vertical lift. Pool pumps don't usually have much vertical lift, but they do have resistance to flow from pipe, elbows, chlorinators, filters etc..

Here's a pretty good explanation of how to calculate head. http://www.poolspa.com/publications/sin/stories/august95/1/pumps.html

Keep in mind that it is not an exact process.

[eljefe281]

There is approximatly 20' between my pool suction and the pump suction, so I will need to check the pump curve at 20' of head.

First, the parameter of interest is total system head, from the pump discharge all the way back to the pump suction. Your statement only considers "suction head".

Also, head is more complex than the straight run distance from point A to point B. A turn in the pipe (elbow) adds a significant amount of head relative to a straight piece of pipe of the same length. Also, there are valves, as well as equipment (filter, heater, etc.) which add resistance.

Calculating total system head is very difficult and imprecise. The consensus on this board is that, after all is said and done, your total system head will be between 45 feet and 65 feet.

Do the same thing you did before, using the upper and lower ends of that range. That will give you a better idea of what you need.

[mas985]

It will be very difficult to find a pump that will have a flow rate that low. Even a two speed pump is likely to exceed that at low speed. So my suggestion would be to look at 3/4 HP two speed pumps as these are about the lowest HP and flow rates you can get on the low speed. You will get about 70 GPM @ 50' head on high speed and 35 GPM @ 13' head on low speed. A bit higher than what you want but it won't cost you too much to run either.

In addition, the Whisperflow 1/2 HP pump has about the same current draw as the 3/4 HP motor. I think it is acutally the same motor and they use a different impeller. So it probably does not pay to go down to the 1/2 HP pump as it will cost the same to run.