Pump and Tank Modeling Parameters

Modeling Storage Tanks: The Key Parameters

In a water model, tanks serve two primary functions: they provide storage to meet fluctuating demands and they help stabilize pressures in the system. While a reservoir is modeled as an infinite source with a constant water level (a fixed HGL), a tank has a finite volume, and its water level—and thus the HGL it provides—can change over time.

To model a tank accurately, WaterGEMS needs to know its physical and operational characteristics. Let's watch a short video that introduces these concepts.

As the video explains, the core parameters for a tank fall into two categories:

1. Operating Levels (Elevations): This defines the vertical range in which the tank operates.

   • Elevation (Base): The elevation of the physical bottom of the tank.
   • Elevation (Minimum): The lowest water level allowed for operation. The usable volume is calculated from this level upwards.
   • Elevation (Maximum): The highest water level allowed, often the overflow level.
   • Elevation (Initial): The water level in the tank at the beginning of the simulation. For a steady-state analysis, this is the most important value as it sets the HGL at the tank's location.

2. Geometry: This defines the tank's storage volume.

   • Diameter: For a simple cylindrical tank, this is all that's needed. WaterGEMS uses the diameter and the height between the minimum and maximum levels to calculate the tank's volume. For more complex shapes, you can define the volume using a level-to-area curve, but the simple diameter is most common.

Now, let's see exactly where you would input this data in the software. The following short clip from a workshop demonstrates the process.

These parameters—levels and diameter—are the essential data points you would need from a client to model an existing tank.

Modeling Pumps: Adding Energy to the System

Pumps are the engines of a water distribution system. They provide the energy (head) needed to lift water to higher elevations and overcome friction losses in the pipes. In the last lesson, you saw this as a sharp, vertical jump in the HGL.

To model a pump, you need to tell WaterGEMS how it performs. This is primarily done through its pump curve and efficiency data.

Let's get a conceptual overview of these critical pump characteristics.

The Pump Definition

The video introduced the core concepts. Now let's get more specific about how you define these in WaterGEMS. You don't just input a single number; you create a "Pump Definition" that contains the pump's performance data.

The most common way to define a pump, especially for freelance projects where you're given manufacturer data, is the Standard (3-Point) Curve. This requires three specific Head vs. Flow data points:

1. Shutoff: The head the pump produces at zero flow.
2. Design: The intended operating point, typically corresponding to the Best Efficiency Point (BEP).
3. Max Operating: The highest flow at which the pump is intended to run.

To see a detailed list of these and other definition types, please review the official Bentley documentation. This will be a valuable reference for you in the future.

Practical Input and Data Sources

You now know the parameters. Let's see them put into action. This clip shows the complete workflow: creating a new pump definition, entering the 3-point curve data, defining its efficiency, and assigning it to a pump element in the model.

Finally, here is a clear image of what those parameters look like in the pump's property window.

A crucial question for you as a freelancer is: Where do I get this data? The next video segment gives you the answer.

Conclusion

In this lesson, we demystified the process of defining the core hydraulic elements that control energy and storage in a water system. You now know the specific, essential parameters required to model tanks and pumps in WaterGEMS.

Key Takeaways:

• Tanks are defined by their operational levels (Base, Minimum, Maximum, Initial) and their geometry (typically a diameter), which together determine their available storage volume.
• Pumps are defined by their performance characteristics, primarily the pump curve (the relationship between head and flow) and the efficiency curve.
• The most common method for defining a pump is a Standard 3-Point Curve, using the Shutoff, Design, and Maximum Operating points.
• This data typically comes from manufacturer catalogs or field tests, and entering it correctly is a non-negotiable step for creating an accurate hydraulic model.

In our next lesson, we will build on what we learned about tanks. We will take a closer look at the distinct hydraulic roles of tanks and reservoirs and clarify when to use each element in your WaterGEMS models.