The Pump junction allows you to model the pressure added to a system by a pump, fan, or blowers (ignoring compression effects). Because all pumps are different, AFT Fathom does not provide any standard pump types. Pressure and flow data that describes the pump must be obtained from the manufacturer or from test data. To reduce repeated data entry, frequently-used pumps can be added to the Component library.

Common Input Information

Like all junctions, pump junctions require a junction number, junction name, and inlet and outlet elevations. Similar to other junctions, pumps can have Design Alerts and Notes applied to them. They require two connecting pipes, unless the Submerged Pump option is enabled. Note that the direction of the connected pipes define what side of the pump is suction and which is discharge.

Pump Model

This tab requires the selection and definition of what type of pump the junction represents. There are three models available:

  • Centrifugal (Rotodynamic) - Represents a typical centrifugal pump where the head added to the fluid is related to the flow through the pump via a pump curve.

    • Interstage Bleed/Takeoff Flow - Represents a multiple stage pump that has some amount of flow removed between the upper and lower stages. Centrifugal (Rotodynamic) must be selected to enable this model.

  • Positive Displacement - Represents a steady state approximation of a positive displacement pump. The flow is fixed to a constant value, and whatever head is necessary to obtain that flow will be supplied.

  • Pump As Turbine - Represents a pump as a turbine which allows the pump to produce electrical power when the pump sees reverse flow.

Variable Speed

This tab allows the speed of the pump to vary either by a fixed amount, or dynamically. These options are only available for a centrifugal pump. A minimum speed can be entered to limit how much the speed is varied.

  • Fixed Speed (%) - Directly modify the pump curve according to the Affinity Laws. The Pump Curve entered in Pump Configuration is always assumed to be the 100% speed curve.

  • Controlled Pump (Variable Speed) - Dynamically change the speed of the pump to meet a specified control setpoint. Instead of allowing the flow or head to vary with a fixed speed, the speed of the pump (and thus Pump Curve, according to the Affinity Laws) varies to meet a fixed flow or head. If modeling a suction or discharge pressure, control can optionally be enforced only if the value is above/below the setpoint.


If heat transfer modeling is enabled, the Thermal tab will appear and heat added to the fluid by the pump due to inefficiency can be modeled. Three options are available:

  • Percent of Ideal Efficiency - Enter the percentage of ideal energy required by the pump that goes into heat addition. Typically, this would equal the actual efficiency subtracted from 100%. For example, if the pump was 70% efficient, the entry here would be 30%.

  • Percent of Inefficiency - Enter the percentage of the lost energy (i.e., the inefficiency) that goes into fluid heating. Typically, this would be 100%, which says that all inefficiency goes into heat.

  • User Specified Heat Rate - Directly enter a heat load which goes into the fluid.

Slurry De-Rating

(SSL Module Only)

Pump head degradation occurs when pumping solids. This is known as de-rating. See the Slurry Pump De-rating topic for more information.


(XTS Module Only)

The pump junction allows modeling of transients to occur in the following pump parameters:

  • Speed (if using a pump curve) for both Pumps and Pump as Turbine

  • Flow rate (if modeling a fixed flow rate)

  • Pressure/head (if modeling a fixed pressure or head rise)

  • Control setpoint

  • Load Rejection for Pump as Turbine

For more information on transient data, including event transients, see Junction Transient Data.


There are several optional parameters that can be defined for a pump. Some of these are available to most junctions such as Initial Guesses, Display on Workspace, Design Factor, and Workspace Icon.

Also present are several pump junction specific options:

  • Special Condition

    • None - The pump operates normally.

    • Pump Off No Flow - The pump is shut off and blocked. This is identical to a closed valve in Fathom.

    • Pump Off With Flow Through - The pump is shut off but allows flow to continue through. This is identical to a lossless connection in Fathom.

  • Number of Pumps at This Location - Several pumps can be represented by one pump junction. This simplifies the model by reducing the number of pipes and junctions present, as well as automatically calculating the resulting composite pump curve based on the user-defined curve. When this option is selected the pump summary will show the total flow/head from the combined pumps.

  • Use Viscosity Correction - Pump performance changes if the system fluid viscosity is different than the pump test fluid viscosity. Viscosity Corrections allow the user to account for these changes.

  • Additional Efficiency Data - Power and efficiency information for each stage in a VFD-Motor-Pump assembly.

Related Blogs

Back to the Basics: Calculating and Defining Head

Not a Leak! Modeling Multi-stage Pumps with Discharge Flow Between Stages

Determine Your Pumps BEP and Know API-610's Recommendations

What Does “Head (HGL)” Mean for Submerged Pumps and Exit Pressures?

SSL Module
Settling Slurry Module
An optional add-on module to AFT Fathom which allows users to simulate settling slurries.
XTS Module
Extended Time Simulation Module
An optional add-on module to AFT Fathom which allows users to simulate system transient behavior.