For the pump in Example 7.1, if the pool size is 10 ft by 20 ft and has water to a depth o...

For the pump in Example 7.1, if the pool size is 10 ft by 20 ft and has water to a depth of 5 ft, how long will it take to completely cycle the water of the pool? A reasonable goal is to recirculate pool water in 8 h. If this is not achievable for a given pump, what could you do to reduce the water turnover time?

Example 7.1

If the swimming pool pump of Figure 7.8 has to pump water through 40 ft of 1.5-in steel pipe, and through elbows and a filter with a total cumulative resistance of K = 2.0, what is the flow rate of water through the system?

SOLUTION The total resistance, or the total head loss, will increase with flow tale in a nonlinear fashion, so there is no explicit solution for this problem. The head loss as a function of flow rate for this system has been calculated in Excel and plotted along with the pump performance curve in Figure 7.10. The point where the two lines cross will be the operating point of the system for the given conditions. For this problem the flow rate will be about 110 gal/min.

FIGURE 7.8 Generic pump performance Curve for a 2-hp swimming pool pump.

FIGURE 7.10 Pump performance curve of Figure 7.8 shown along with the system curve for Example 7.1.

Most manufacturers provide more information on their pump curves than a single performance curve at constant speed. Figure 7.11 shows a graph from a manufacture for a specific model that shows performance curves for three different sizes of piping along with the efficiency of the pump at different points and the NPSH of the pump.

FIGURE 7.11 Pump performance curves. Courtesy of Split Flow™ Pumps.