Water at 80°F is flowing in a river 130 ft below a water storage tank. The tank holds water drawn from the river with the use of a pump delivering 100 gal/min. The inlet and discharge elevations of the pump are both 15 ft. Set the river depth at 13 ft and the fluid level in the tank at 15 ft. The

Question

Water at 80°F is flowing in a river 130 ft below a water storage tank. The tank holds water drawn from the river with the use of a pump delivering 100 gal/min. The inlet and discharge elevations of the pump are both 15 ft. Set the river depth at 13 ft and the fluid level in the tank at 15 ft. The pipe to be used is Schedule 40 plastic PVC, and the total pipe length is 155 ft. Design the pipe size for a velocity of 8 ft/s. There is a pressure of 30 psi in the storage tank so it can be distributed for various uses. There are (2) 90° standard elbows and a foot valve on the suction line. There are (2) 45° standard elbows on the discharge line. Use PIPE-FLO® to calculate the total head on the pump, select a commercially available pump, show the pump curve, and summarize the major system design decisions.

Accepted Answer

Begin by using the “system” menu to establish the units for the problem, fluid zones, and pipe specifications. Since the problem statement says to design the piping at a nominal velocity of 8 ft/s, this must be accounted for when establishing the pipe specifications. In the pipe specifications menu, under “Sizing Criteria,” choose “Design Velocity” then enter the 8 ft/s value. This will allow for later calculation of a pipe size for a given flow rate. See the figure below for reference.
Next place the two “tanks” into the system. Right click on the symbols and select “CHANGE SYMBOL.” Change one tank to make it appear as a river, and the other as a closed tank. Be sure to include the values from the problem statement for these two items in the properties grid.
Add in the sizing pump and enter its data into the properties grid.
Draw in the pipe to connect from the river to the pump. Assume that the length of this piece of pipe is 15 ft. Since a pipe size hasn’t been specified, the “Design for Velocity” feature of PIPE-FLO® can be used to calculate an appropriate size. To do this, click on the pipe and begin entering the appropriate values in the property grid. To calculate an appropriate pipe size, click the “. . .” button that appears to the right of the pipe size box in the properties grid. A sizing calculator appears on the screen; fill in the required data and PIPE-FLO® will show the calculated size. For this example problem, a specified flow rate of 100 gal/min and velocity of 8 ft/s gives a recommended pipe size of 2.5-in Schedule 40. Continue entering the data in the property grid, including the foot valve and elbows, until the pipe is fully defined. See the figure below as a reference for the pipe size calculator.
Repeat the same process for the discharge pipe from the pump to the storage tank. Assume the total length of this pipe is 140 ft. Be sure to include all fittings and valves when drawing in the pipes.
Once all the data have been entered run the PIPE-FLO® calculations to find the total head on the pump, suction pressure, discharge pressure, etc. Again, these calculated values will be used to help determine an appropriate commercially available pump to simulate the actual results. The solution to the first half of the problem is shown below. The total head calculated is 218 ft as seen in the system drawing and in the enlarged image of the sizing pump data.
Now that the initial data have been established for the system, the results can be used to select a commercially available pump. To do this, right-click on the sizing pump and choose “Select Catalog Pump. . .” from the menu. A pump selection menu appears on the screen. In the demo version of the software, these are not actual pumps, but are very typical of commercially available pumps. The full version connects to actual pump curves that you could then specify and procure for the application.
From the “Select Catalog” drop-down box, choose “Sample Catalog.60.” This is the sample catalog for pumps with 60 Hz motors; the common frequency for power supply in the United States. 50 Hz options are available for users in countries other than the United States. From the “Types” menu, check all of the boxes so that all pump manufacturers are shown. In the “Speeds” menu, check only the 3600 and 1800 options. These values represent the nominal speeds for the most common AC motors used to drive pumps. The actual speeds will be slightly lower and they are listed with the pump data. Pump curves now appear below in the same “Pump Selection” menu for all the applicable pumps; see the figure below.
PIPE-FLO® automatically sorts the available pumps such that the optimum pump is first on the list, as indicated by the efficiency at the operating point for the pump. A sample pump curve is displayed, and a marker on the pump curve indicates where the particular system you are using falls on the curve for that specific pump. For this example, we will choose the first pump on the list and use the PIPE-FLO® recommendation.
Highlight the pump that is to be used in the system, and click the “Select Pump” button at the bottom of the page. This automatically replaces the sizing pump in the problem with the commercially available pump that was just chosen. If the calculate button is pressed again after the pump has been replaced, other values such as power and efficiency for the commercially available pump are displayed on the FLO-Sheet®. The results for this example problem are shown below.
Note that PIPE-FLO® doesn’t rename the pump after a commercially available one has been chosen since it is assuming the user is entering names for all the components. The way to tell if the pump has actually changed from the sizing pump to the commercially available one is by the calculated results shown. If power and efficiency are listed, the user knows that the commercially available pump is being listed in the problem since these values aren’t given for a sizing pump.
Summary: The pump designation and its major performance parameters are:
a. Operating point: 100 gal/min flow rate at 218 ft of total head
b. Pump: 1 ½ × 1 × 8 centrifugal pump; ESP-type; Pump curve ABC1055-1
c. Pump speed: 3500 rpm Impeller diameter: 7.125 in
d. BEP: 61.1 percent
e. Efficiency at operating point: 58.7 percent (within 96 percent of BEP and to the left of BEP) f. The software chose a plastic pipe size for the system to be 2½-in Schedule 40 for both the suction and discharge pipes based on the desired flow velocity of 8.0 ft/s. The actual flow velocity is 6.70 ft/s.
g. A gradual reducer is required at the pump inlet from 2½-in to 1½-in sizes, and a gradual enlarger is required at the pump outlet from 1-in to 2½-in sizes.
h. The [latex] NPSH_A[/latex] for the suction inlet to the pump is computed to be 29.06 ft.
i. The value for [latex] NPSH_R[/latex] for the pump and additional operational data for the pump can be accessed from the software.

Question 13.5: Water at 80°F is flowing in a river 130 ft below a water sto...

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