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Delaying Flow
Blocks of interest
The “Rates, Constraints, and Movement” chapter discussed how to specify critical constraints (such as a Valve’s maximum rate) and the factors that determine the actual speed of flow mov- ing through a model.
☞ Since the concepts of flow rules and critical constraints are central to the discussion of delay- ing flow, it is assumed that you have already read the “Rates, Constraints, and Movement” chapter.
This chapter describes how to use advanced methods to delay flow – for a specified period of time or until a specified condition has been met, either blocking the movement of flow or maintaining it at a certain speed. It illustrates several methods for delaying flow, including how to:
• ControlhowandwhenaValveobservesorignoresitsmaximumratesetting:
• Setting a goal for a quantity of flow
• Setting a goal for a duration
• Using hysteresis to control when the block’s maximum rate will be observed
• UseaShiftblock(Itemlibrary)withaConveyFlow,Interchange,Tank,orValvetodelay flow movement for a specified period of time
• Transport flow over a defined distance at a specified speed with a Convey Flow block
☞ Most of the models illustrated in this chapter are located in the folder \Examples\Discrete Rate\Delaying Flow. The tutorial models mentioned are located at \Examples\Tutorials\Dis- crete Rate.
Blocks of interest
The following blocks from the Rate library will be the main focus of this chapter.
Convey Flow
Delays the movement of flow from one point to another. Can accumulate flow to a maximum density, accumulate flow to fill empty sections, or act as a non-accumu- lating conveyor.
Controls and monitors the flow, limiting the rate of flow passing through. This block can also be used to set a goal for the duration of flow movement or the amount of flow.
Controlling a Valve’s maximum rate
The section “Defining a critical constraint” on page 376 showed how to set a Valve’s maxi- mum rate. Options on the Valve’s Flow Control tab provide advanced control over how and when the Valve applies its maximum rate. These settings determine when the Valve’s maxi- mum rate is observed or ignored, and for how long.
The advanced control options include:
• Setting a goal for a certain quantity of flow to pass through the Valve.
• SettingagoalforhowlongflowcanmovethroughtheValveorforhowlongitshouldbe stopped from moving.
• Determining what happens when the goal ends.
• UsinghysteresistodelaytheValve’sresponsetosystemrequirements.
Discrete Rate

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