The system resistance curve is a plot of a piping system's total resistance over a range of flow rates. You can automatically generate a system resistance curve in PIPE-FLO, however this feature has the following limitations:
- There can only be one active pump in the system (all other pumps are shut off).
- The program sets all controls (FCVs, PRVs, and BPVs) in the system to fully open.
- The program sets all flow demands in the system to zero.
Because of the above limitations, this feature cannot be used in more complex systems. However, by setting the system pump to operate at a fixed flow rate, you can obtain the data necessary to generate a system resistance curve.
For the system shown below in Figure 1, a system resistance curve cannot be generated because the system has more than one loop:
NOTE: In addition to the typical definition of a loop (a closed circuit of piping that begins and ends at the same point), a loop is also defined as a path from one set pressure to another.
For this system, we will generate a system resistance curve by running five lineup calculations with the pump flow rate set over the range of the operation (from 0 to 200 gpm). When you set a pump to operate at a fixed flow rate, PIPE-FLO determines the total dynamic head (TDH) required for the pump. To set the pump operation to fixed flow rate:
- Double-click on the pump to display the Pump dialog box.
- In the Lineup Settings group box, select the Set flow rate to option button and specify the flow rate through the pump.
- Click OK
After you set the pump flow rate, run the lineup calculation and note the TDH calculated for the pump. This is the resistance in the system at specified flow rate. Repeat this process for the remaining curve data points.
For the system shown in Figure 1, the following data points were obtained:
Next, the data was entered in Excel and the following curve was generated:
If you are going to select a pump using PIPE-FLO's pump selection module, you can enter the resistance curve data and the program will plot it along with the pump performance curve.