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Applies To |
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Product(s): |
HAMMER |
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Version(s): |
CONNECT Edition, V8i |
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Area: |
Modeling |
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Original Author: |
Scott Kampa, Bentley Technical Support Group |
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Problem
After computing a pump shutdown or start-up in HAMMER, it looks like the operating rule is not being followed.
Solution
This could be occurring because of the value entered for the property "Time (For Valve to Operate)". This represents the time from the start of a calculation for a control valve on a pump to close or open. Since the value entered is calculated from the start of the model run, and it will override the operating rule, it can affect the way the results look after computing the transient analysis.
Pump startup (initially off)
When the pump is initially off, the "Time (For Valve to Operate)" represents the time (from start) that a built-in valve will open. For example, if you enter a value of 2 seconds along with a pump startup, the pump valve will be initially closed and will open linearly from time zero to 2 seconds, with no assumed check valve. If your pump's downstream HGL is higher than it's upstream HGL, this can result in reverse flow at the beginning of the transient simulation.
If the control valve is a check valve, you will want to enter a value of zero seconds. (a special trigger to model a check valve) For more complex pump valve modeling, use a separate valve node such as a TCV. More on valve closure here.
Note: if you are seeing a delay between when the operating rule turns on the pump and when flow first occurs, see below article:
Flow from pump is delayed after pump startup
Pump shutdown (initially on)
When the pump is initially on, the "Time (For Valve to Operate)" represents the time (from start) that a built-in valve will close. For instance, if you enter a value here of 2 seconds, the program will close the pump between time zero and 2 seconds after the model run starts. This can result in a surge that you did not intend to generate. If there is no valve on the pump at all, enter a very large number, like 999,999 seconds to assure that it will not affect your model run.
If the control valve is a check valve, you will want to enter a value of zero seconds. (a special trigger to model a check valve) For more complex pump valve modeling, use a separate valve node such as a TCV. More on valve closure here.
See Also
Modeling a Pump Start-Up Transient Event in HAMMER
Modeling a Pump Shut Down Transient Event