Modeling Reference - Valve With Linear Area Change [TN]

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Document Information

Document Type: TechNote

Product(s): Bentley HAMMER Version(s): V8i Original Author: Jesse Dringoli, Bentley Technical Support Group

Overview

This technote explains how the Valve with Linear Area Change element works and its typical application in HAMMER V8i. It also provides an example model file for demonstration purposes.

How it Works

The "Valve with Linear Area Change" element represents a simplified valve that either closes linearly (with respect to area) or acts as a check valve that stays closed upon reverse flow. The user only specifies a time to close, so no delay can be incorporated with the closure. Meaning, it starts closing as soon as the transient simulation begins.

When to Use it

This valve is useful for verifying best-case assumptions or representing motorized valves. For example, you could quickly check the transient effects of a valve closing linearly over a period of time, without having to set up a time vs. closure pattern. Then if the results are satisfactory, you could replace it with a TCV including an operating rule to define a more complex/precise operation.

The check valve feature of this valve is not commonly used, since you can use the check valve feature of the pipe element or the check valve node itself. It is a bit different than the other check valves though, as it cannot reopen upon pressure differential. This might represent a check valve with a mechanism to hold the valve shut.

During the initial conditions (EPS or steady state) this element is treated as a GPV (general purpose valve), with a flow vs. headloss rating curve based on the discharge coefficient entered in the valve's properties.

Attributes

"Time to Close" - The delay until the valve fully closes. The valve closes linearly between time zero and the value you enter here. Entering a value of zero causes this valve to act as a check valve that stays closed after reverse flow is detected.

"Discharge Coefficient" - This is used to determine the flow/headloss relationship of the valve during the initial conditions. For example if the valve is fully open before the transient simulation, there will still be some headloss through it. So, you would enter the discharge coefficient describing the loss through that fully open valve. The transient simulation uses this coefficient to compute other flows and headlosses through the valve as it closes. As the valve closes, the user-entered discharge coefficient is linearly reduced to zero over the "time to close".

"Status (Initial)" - Used to determine the status of the valve during the initial conditions. When "active", the "discharge coefficient" determines the headloss through the valve during the initial conditions.

Example Model

Click to Download Note: the above model is for example purposes only. It can be opened in version 08.11.00.30 and above and you can find additional information under File > Project Properties.

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