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``````382 Rates, Constraints, and Movement
Meeting the critical constraint requirement
Proportional mode
The top section of the Minimum Value model indi- cates the critical constraint requirement when a Merge or Diverge block is in Proportional mode. If the block is located between two residence blocks, only one critical constraint is needed as long as the branch's proportion is neither 0 nor blank. (This lower requirement for constraints is an exception to the general rule described on page 380.) The effec- tive rates for the other branches are deduced from the Valve's maximum rate.
In the Minimum Valve example shown on the right, a Valve is placed on a Diverge block’s bottom outflow branch, and that branch does not have a 0 or blank proportion.
Priority mode
Only one constraint needed
The lower section of the Minimum Value model indicates the critical constraint requirements when a Merge or Diverge block is in Priority mode. In this case, the number of critical con- straints that must be placed on the branches between residence blocks depends on where those constraints are placed. These situations are shown in the Minimum Valve model.
If a critical constraint is placed between a residence block and a Diverge block’s inflow branch, you do not need to place any other critical constraints on the Diverge block’s outflows. Likewise, if you place a critical constraint on a Merge block’s outflow branch, you do not need to place any critical constraints on its inflow branches. This is shown on the right, where a Valve with a maximum rate greater than or equal to 0 but less than 1e10 (the infinite rate) is on a Diverge block’s inflow branch and there are no critical con- straints required on its outflow branches.
No constraint on each outflow
Constraint on each outflow
If you don’t
place a critical constraint on a Diverge block’s inflow branch, you must place at least one critical constraint on each outflow branch. Likewise, if you don’t place a critical constraint on a Merge block’s outflow branch, you must place at least one critical constraint on each inflow branch.
This is shown in the screenshot to the left, where there is no critical constraint on the Diverge block’s inflow branch. This means each outflow branch must have a critical constraint, in this case a Valve with a maximum rate greater than 0 but less than 1e10 (the infinite rate).
Discrete Rate

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