Backflow Assembly Sizing Screen
Hazard-driven assembly selection (RP required for any high / health hazard per IPC 608).
Example
You enter
- Service flow demand (GPM) 100
- Hazard category (IPC 312) high
- Intended assembly type DC
- Service / assembly size (in) 2
- Upstream supply pressure (psi) 70
You get
- Head loss at design flow 11.5 psi
- Pressure remaining downstream 58.5
Checked against published worked examples from: IPC / AWWA / EPA.
Details, formula, and sources
ScopeHead loss at design flow from the bundled assembly curves, the pressure remaining downstream, and the IPC 312.11.2 (312.10.2 in 2021) / AWWA M14 annual-test reminder.
Formula or tableRequired 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.
Source and editionIPC 2027 §312 (cross-connection control) and AWWA M14 (Backflow Prevention and Cross-Connection Control) by name; IPC 2027 §312.11.2 [312.10.2 in IPC 2021] (testing at installation and at least annually) and §608.1 / Table 608.1 (assembly by hazard) by section. Head-loss curves from data/plumbing/backflow-curves.json (Watts technical bulletins, representative).
Free accessFree read-only access at codes.iccsafe.org.
What governsEstimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.
API field namesservice_flow_gpm, hazard, assembly_type, pipe_size_in, upstream_pressure_psi, head_loss_psi, downstream_psi
- High-hazard rule reduced-pressure principle (RP) assembly requiredIPC 2021 §608.1 / Table 608.1
- Minimum residual 20 psi default (user-adjustable)engineering practice
- Annual test tested at installation and at least annuallyIPC 2027 §312.11.2 [312.10.2 in 2021] / AWWA M14