Modeling a Vertical Turbine Pump 

Vertical turbine pumps are multistage pumps commonly used in municipal water supply, waste water treatment, reservoir management, HVAC and other markets. They are distinguished by the bowl shape impeller casings stacked vertically. The pumps are often submerged and placed in a well, however, some applications place the bowl assemblies in a metal can and the entire pump is mounted above the ground.

Modeling a vertical turbine pump in PIPE-FLO® requires gathering information about the tank, pump and pipes, and then following four steps. These steps include adding different fixed K resistance coefficients in two pipe lines that account for losses not associated with standard pumps. This article reviews the four step process and includes a spreadsheet to aid in calculating the fixed K losses. A PIPE-FLO® Professional model and screenshots are also included in the article.

 

Design Data

For the fluid source, you need the following data.

  • Elevation at the bottom of the source. This will be your datum elevation plane (ft). 
  • Fluid level of the source measured up from the datum elevation plane (ft), dimension D.

For the pump, you will need the following data.

  • Vertical Turbine pump performance data based on the whole pump assembly (ft vs. gpm).
  • The height of the suction case inlet measured up from the datum elevation plane (ft), dimension A
  • Pump suction and discharge elevations. Suction elevation is the height of the eye of the first stage impeller, measured up from the datum elevation plane (ft), dimension B. The discharge elevation is the height of the center line of the discharge flange measured up from the datum elevation plane (ft), dimension C.
  • Column pipe internal diameter (in), length (ft) dimension E, and absolute roughness (in).
  • Pump shaft diameter (in).
  • Discharge elbow type, (cast or fabricated).
  • Discharge flange internal diameter (in).
  • Suction screen area ratio (open area/total area).

For the fluid, you need the following data.

  • Design Flow Rate (gpm).
  • Fluid Density (lb/ft³) (can be taken from the fluid zone in PIPE-FLO®).
  • Absolute viscosity (cP) (can be taken from the fluid zone in PIPE-FLO®).

Building the Model 

Once all of the information is obtained, you can follow the four steps listed below to model a Vertical Turbine inside PIPE-FLO® Professional.

Fixed K values are added to the model to account for the suction screen, column pipe as an annulus, and discharge elbow losses. If a fixed K value is calculated from a pipe size other than the size selected in the pipe dialog box, then that fixed K value has to be adjusted to the size selected in PIPE-FLO. The attached spreadsheet performs the fixed K pipe size adjustment and no additional calculations are necessary. The formula used to make the adjustment in the spreadsheet comes from the Flow of Fluids Technical Paper 410, by the Engineering Department of the Crane Company, page 2-9, equation 2-9. 

Step 1: Tank

The fluid source will be modeled as a tank.
- Install a tank with the bottom elevation equal to the datum elevation plane. All elevations in the model are measured using this datum elevation plane as a reference. The liquid level in the tank is the height of the fluid measured up from the datum elevation plane, dimension D.

Step 2: Suction Case Pipe With a Fixed K1 Screen

- Connect a pipe representing the screen and suction case to the tank with a small length equal to the casing length (example 1 ft). Next, select a pipe size from the pull down list equivalent to the size of the suction flange of the first bowl. Make sure the suction case roughness matches the roughness of the pipe specification inside PIPE-FLO®.
The suction case pipe should penetrate the tank at a height equal to dimension A. If a screen is attached to the suction case, add a fixed K1 to the pipe that represent the resistance. An Excel spreadsheet is attached that determines the suction screen K1 based on open/total area ratio. The open/total area ratios can be found in the drop down list in the spreadsheet. The fixed K1 value from the spreadsheet is then added to the suction case pipe using the K (Valves & Fittings) option found in the Property Grid's Pipe Design by imputing the corresponding fixed K1 value. If the suction flange size of the first bowl is different from the pipe size selected inside PIPE-FLO®, the spreadsheet will automatically make the fixed K adjustment.

Step 3: Pump

- Install a pump on the open end of the suction case pipe and enter the pump performance data. The pump suction elevation, is the height of the eye of the first bowl's impeller, measured up from the datum elevation plane, dimension B. The pump discharge elevation, is the height of the center line of the discharge flange, measured from the datum elevation plane, dimension C.

Step 4: Column Pipe

- Connect a pipe from the pump to an open node. This pipe will represent the column and discharge elbow of the pump. Annulus calculations are used to represent the column pipe losses with the internal pump shaft. For simplification, the column pipe losses with the internal pump shaft and the discharge elbow losses can all be accounted for by a fixed K2 value. The attached spreadsheet performs the annulus column pipe loss calculations allowing the user to select a discharge elbow type from a drop down list. The spreadsheet totals the column pipe loss and the discharge elbow loss into a total fixed K2 valve and makes any pipe sizing fixed K adjustments that are needed. The fixed K2 value from the spreadsheet is then added to the column pipe using the K (Valves & Fittings) option found in the Property Grid's Pipe Design by imputing the corresponding fixed K2 value.

 

 

 

PIPE-FLO® Example 

The following is a PIPE-FLO® Professional example model for a vertical turbine pump (see attachments). The tank bottom elevation is equal to the datum elevation plane and the tank has a fluid level of 6 feet. The suction case is 1 foot off the bottom of the tank, the pump's first impeller is 2 feet off the bottom of the tank and the center line of the discharge flange is 15 feet off the bottom of the tank. The column pipe is 10 feet long and the discharge elbow was cast. The dialog boxes associated with each device are also shown.

Note the fixed K values are show for the suction case and column pipes.

The tank dialog box is shown below.

This dialog box above shows the bottom elevation at zero and the fluid level at 6 feet.

The suction case pipe dialog box is shown below.


This dialog box above shows the pipe at 1 foot in length and 10 inches in diameter.

The tank configuration dialog box is shown below.

The penetration height of the suction case pipe into the tank is added under the tank configuration tab. A tank penetration height of 1 foot means the suction case pipe starts 1 foot off the bottom of the tank. A pipe has to be created before the penetration height can be added to the tank configuration dialog box.

The suction case valve & fitting dialog box is shown below.

The suction screen fixed K1 value from the spreadsheet is added to the suction case pipe in the Valves and Fittings dialog box, selecting the Fixed K option. In the above example, the fixed K1 value of 0.32 was added to the suction case pipe. The value 0.32 came from the attached spreadsheet. It is based off the ratio of the open area divided by the total area of the screen. In the spreadsheet, multiple area ratios are listed under a drop down list. The fixed K of 0.32 was found under the area ratio of 0.80. No fixed K adjustments were needed because the actual suction case pipe size was equal to pipe size added to PIPE-FLO®. The screen fixed K area ratio method is from Handbook of Hydraulic Resistance, written by I. E. Idelchik, page 522. 

The pump dialog box is shown below.

This dialog box shows the suction elevation of 2 feet, which represents the height of the eye of the first bowl's impeller from the datum elevation plane, dimension B. The discharge elevation of 15 feet represents the height of the center line of the discharge flange off the bottom of the tank, dimension C. The vertical turbine pump performance data would be entered by clicking the "Enter Curve" button.

The column pipe dialog box is shown below.

This dialog box is showing the column pipe as being 0.001 feet in length, 10 inches in size (the same as the actual discharge flange pipe size), attached to the discharge of the pump (elevation 15 feet) and as having an outlet elevation of 15 feet, dimension C. Since, the size of the column pipe (10 in) is entered in PIPE-FLO®, but this size is not equal to the hydraulic diameter of the annulus, the fixed K2 has to be adjusted. The spreadsheet performs this pipe size fixed K2 adjustment automatically.

Fixed K1 and K2 Resistances Coefficients: 

In the attached spreadsheet, data from the system and from PIPE-FLO® is entered into the yellow highlighted cells. The suction screen ratio and the discharge elbow type have drop down lists. The suction screen area ratio drop down list is shown below.

From the spreadsheet, the suction screen loss (K1) and the column loss plus discharge flange loss (K2) are calculated. K1 and K2 are in red cells. These K values are then added to the Suction Case pipeline and the Column pipeline in the PIPE-FLO® model. 

The spreadsheet and a fixed K dialog box are shown below.

Note that the discharge head and the wire screen area ratio have drop-down lists to choose from.

The column pipe annulus loss and the discharge flange losses K2 are added to the column pipe in the Valves and Fittings dialog box, selecting the Fixed K option. The following screenshot shows the fixed K2 value of 1.1099 being added to the column pipe.

Additional System:

Additional system piping could be added downstream of the Discharge Flange Node. An example system is shown below.

Summary

Modeling a vertical turbine pump in PIPE-FLO® Professional requires finding information on the tank, pump and the piping system. Once the information is gathered and entered into PIPE-FLO®, the results accurately describe a vertical turbine pump in a hydraulic network.

Attachments:

PF VT FINAL sept 10.pipe

VT spreadsheet FINAL Sept 10.xlsx