Sewergems Percent Full Constraint w.r.t Pipe Diameter

I see you attached your model so I took a look. First, the "Design Percent Full" field will not update unless you are using local design constraints. In other words, it's actually an input field when using local constraints, and does not display the global part full design percent from the table you entered. Instead, you should look at the "capacity (design)" compared to the flow through the pipe.

The next problem is that the "rise" values that you entered in the part full design table do not match with any inside diameter values in your conduit catalog. They match the labels of the conduit catalog entries (160, 200, 250, 315), but the design constraint in question refers to the internal diameter (rise), which are 150.6, 188.2, 235.4 and 296.6, respectively. I have added a note about this in the wiki article the Yashodhan mentioned at the bottom of his reply.

If you change the part-full design constraint table accordingly to match the actual inside diameters then re-run your design, the design capacity will appear as expected.

When using part-full design, a pipe with the respective size will attempt to be designed such that the flow through it is less than the flow when calculating normal depth equal to the given percentage of the pipe's rise. For example you have entered 75% for "250" mm pipes (235.4 mm) - this means that the design capacity (desired max flow) is the flow when normal depth is 176.55 mm (75% of 234.5 mm). If you solve the Manning equestion for this pipe with a normal depth of 176.55 mm, you will get a flow of 27.05 L/s. This is what you see in this conduit for the "Capacity (Design)". The flow through this pipe is 14.00 L/s, so it means the constraint. If for example you run a regular analysis run with the size set to the next lowest of "200" (188.2 mm), the design capacity is 8.17 L/s, which is less than the flow through the pipe (14 L/s). This explains why the design solver is choosing the "250" size for that pipe.

I see you attached your model so I took a look. First, the "Design Percent Full" field will not update unless you are using local design constraints. In other words, it's actually an input field when using local constraints, and does not display the global part full design percent from the table you entered. Instead, you should look at the "capacity (design)" compared to the flow through the pipe.

The next problem is that the "rise" values that you entered in the part full design table do not match with any inside diameter values in your conduit catalog. They match the labels of the conduit catalog entries (160, 200, 250, 315), but the design constraint in question refers to the internal diameter (rise), which are 150.6, 188.2, 235.4 and 296.6, respectively. I have added a note about this in the wiki article the Yashodhan mentioned at the bottom of his reply.

If you change the part-full design constraint table accordingly to match the actual inside diameters then re-run your design, the design capacity will appear as expected.

When using part-full design, a pipe with the respective size will attempt to be designed such that the flow through it is less than the flow when calculating normal depth equal to the given percentage of the pipe's rise. For example you have entered 75% for "250" mm pipes (235.4 mm) - this means that the design capacity (desired max flow) is the flow when normal depth is 176.55 mm (75% of 234.5 mm). If you solve the Manning equestion for this pipe with a normal depth of 176.55 mm, you will get a flow of 27.05 L/s. This is what you see in this conduit for the "Capacity (Design)". The flow through this pipe is 14.00 L/s, so it means the constraint. If for example you run a regular analysis run with the size set to the next lowest of "200" (188.2 mm), the design capacity is 8.17 L/s, which is less than the flow through the pipe (14 L/s). This explains why the design solver is choosing the "250" size for that pipe.