Creating a timer control to execute after a specific time period has elapsed

Applies To
Product(s): WaterCAD, WaterGEMS, HAMMER
Version(s): CONNECT Edition, V8i
Area: Modeling
Original Author: Mark Pachlhofer, Bentley Technical Support Group

Problem Description

Is it possible to have a control that works based on a specifc elapsed time period? Can I have a control that makes an FCV close 30 minutes after a tanks becomes full?


This is possible, but it's easier explained when looking at the attached sample model.

In the upper part of this model surrounded by a box you will see there is a timer built from 2 reserviors, a tank, and junction with a demand on it. Open the controls dialog (Components > Controls) to more easily understand what is occurring.

The timer control: Pipes P-1 and P-3 are initially open, so the system disconnected user notification doesn't trigger. This is because J-1 needs flow to satisfy the demand on it all the time and T-1 needs another boundary element to be connected to it. This is all set up in the properties of the elements.

When the timer starts pipes P-1 and P-3 are closed and P-2 opens. This is done by the control with the ID LC140 that states:

IF T-215 Hydraulic Grade > 925.00 ft And FCV-1 Status = Inactive  THEN P-1 Pipe Status = Closed , P-3 Pipe Status = Closed , P-2 Pipe Status = Open

From this control it can been seen the timer starts when the real tank in the model, T-215, is greater than an HGL of 925 ft. When the timer stops it resets everything, so it can be used over again based on this control statement:

IF T-1 Hydraulic Grade <= 50.00 ft THEN FCV-1 FCV Setting = 50.00 gpm, P-3 Pipe Status = Open , P-1 Pipe Status = Open , P-2 Pipe Status = Closed

This allows tanks T-1 to refill (this is the timer tank) and allows the re-use of the timer.

The part that you need to work out is the timer portion (i.e. the size of the tank). What you want to do is set the tank diameter based on the total active volume to demand (in junction J-1) relationship. You have to set it so that it will drain in the exact amount of time needed to turn on your pump or in the case of the example to trigger the FCV to engage. For example, if you want to drain your tank in 30 minutes you could have a tank with a volume of 30 gallons that drains at 1 gpm per minute. If you wanted to do this you would then add a 1 gpm demand on J-1. In the model you can see there is a 10 minute timer, so the total active volume is 10 gallons. The tank starts at the top with an HGL (or elevation) of 60 ft. and drains down 10 feet to an HGL of 50 ft. At this point this control kicks in IF T-1  Hydraulic Grade <= 50.00 ft THEN FCV-1 FCV Setting = 50.00 gpm, P-3 Pipe Status = Open , P-1 Pipe Status = Open , P-2 Pipe Status = Closed, which stops the draining and triggers the action you want to initiate.

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