Backflow Assembly Sizing Screen
Hazard-driven assembly selection (RP required for any high / health hazard per IPC 312), head loss at design flow from the bundled assembly curves, the pressure remaining downstream, and the EPA 40 CFR 141.85 / AWWA M14 annual-test reminder.
Formula and source
Required assembly from the hazard category (high / health hazard requires a reduced-pressure principle assembly). Head loss at design flow interpolated from the bundled assembly curves; downstream pressure = upstream supply pressure − head loss; flag when downstream is below the minimum residual.
IPC 2021 §312 (cross-connection control) and AWWA M14 (Backflow Prevention and Cross-Connection Control) by name; EPA 40 CFR 141.85 (annual testing) by section. Head-loss curves from data/plumbing/backflow-curves.json (Watts technical bulletins, representative).
Audience
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Posture
Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.