# Modeling Tide Changes at a Desalination Plant with Overtime

Question: How can you use Overtime with PIPE-FLO Professional to plot a VFD (variable frequency drive) controlled well pump as the tide changes at a desalination plant?

In the following desalination plant model, the well level changes with the tide. Using PIPE-FLO Overtime you can plot the well pump's VFD speed results as the tide changes.

The components are a well (tank), submersible pump, filter, and another process tank. Well elevation is 0 feet and at high tide, the tank level is 25 feet. Low tide is represented with a tank level of 11 feet. The submersible pump is connected to the well tank with a large diameter pipe of negligible length, representing minimum friction loss. The tide varies by as much as 15 feet and this is represented as a custom curve you input into Overtime. An example 24-hour custom tank level curve is show below. (Details on entering a custom curve in Overtime can be found here.)

So in our example, the pump must be defined in PIPE-FLO as a Variable Speed Pump and a set speed chosen in order for Overtime to be able to create a graph. Our example uses 1000 gallons per minute.

This allows Overtime to graph the changing pump speed. Next, click the calculate button to enter a time period and how many times per hour you want Overtime to make a calculation. Based on our specified duration, Overtime runs a simulation for multiple hours with one calculation per hour.

Lastly, a graph is created displaying pump speed results. This dialog box is shown below.

Overtime then graphs the results. Displayed below are two graphs showing the tank level changes and the pump speed results. The pump speed can be read from the graph as it relates to the tidal change.

A sample system is attached.

By graphing the desalination plant using Overtime, it is easy to compare the pump speeds and when the tanks will be at their lowest points. This type of analysis will allow you to determine the optimal operation for the system.