Septic LPP Orifice Flow and Squirt Height
Per-orifice flow, orifice count, and system flow for a low-pressure-pipe septic lateral.
Example
You enter
- Orifice diameter (in) 0.25
- Squirt height (ft) 5
- Discharge coefficient Cd 0.6
- Orifices per lateral 10
- Number of laterals 4
You get
- Flow per orifice 1.65 gpm
- Total orifices 40
- System flow 65.8 gpm
Checked against published worked examples from: Orifice-discharge equation / university extension LPP design guidance.
Details, formula, and sources
ScopePer-orifice flow, total orifice count, and system flow for a low-pressure-pipe or mound distribution lateral via the orifice-discharge equation. Orifice size, spacing, and layout come from the permitted onsite design.
Formula or tablePer-orifice flow (gpm) = 19.63 x Cd x d_in^2 x sqrt(h_ft) (Cd 0.6 gives the familiar 11.79 coefficient); system flow = per-orifice flow x orifices per lateral x laterals.
Source and editionStandard orifice-discharge equation; university onsite-wastewater extension low-pressure-pipe design guidance, by name.
Free accessExtension LPP design guidance free on land-grant university extension sites.
What governsEstimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.
API field namesorifice_dia_in, squirt_ft, cd, orifices_per_lateral, num_laterals, per_orifice_gpm, total_orifices, system_gpm
- Discharge coefficient Cd 0.6 default (gives the 11.79 / 19.63x0.6 orifice coefficient); editableorifice-discharge equation
- Squirt height target roughly 2.5 to 5 ft (about 1 to 2 psi) for LPP, higher for mound or dripextension LPP design guidance
- Ten-percent rule a uniform squirt requires distal-to-proximal flow to vary by less than about 10%; orifice size, spacing, and layout come from the permitted onsite designextension LPP design guidance