Reducer Centerline Offset and Invert Continuity
The centerline offset = (large OD - small OD) / 2 and which surface stays continuous through a size change.
Example
You enter
- Large-end OD (in) 6.625
- Small-end OD (in) 4.5
- Lay length (in, B16.9 / fitting) 7
- Reducer type eccentric-flat-bottom
You get
- Centerline offset 1.0625
Details, formula, and sources
a concentric reducer holds the centerline but drops the invert (a dam on a gravity drain, an air pocket on a pump suction); an eccentric flat-on-bottom holds the invert (correct on a sewer); flat-on-top holds the crown (correct on a pump suction). A 6 x 4 reducer offsets 1.0625 in. Standard lay lengths per ASME B16.9 (entered by the user); the lay length is a fitting dimension, not a code minimum.
centerline_offset = (large_od_in - small_od_in) / 2. concentric: centerline continuous, invert rises and crown drops by the offset. eccentric-flat-bottom: invert continuous, centerline and crown drop. eccentric-flat-top: crown continuous, centerline and invert rise.
First-principles geometry; the standard lay lengths per ASME B16.9 (bundled value entered by the user; a non-standard reducer overrides), and the flat-on-bottom-holds-invert / flat-on-top-holds-crown practice, by name. Not edition-bound for the offset.
The offset is half the OD difference, a one-line geometric relation; which surface stays continuous follows from the reducer type. All public.
Estimate. AHJ and licensed professional govern.
Field names used by the API: large_od_in, small_od_in, lay_length_in, type, centerline_offset_in
- Offset centerline offset = (large OD - small OD) / 2, independent of the reducer typegeometry
- Lay length standard end-to-end lay length per ASME B16.9 by size pair (user-entered; override for a non-standard reducer)ASME B16.9
- Continuity flat-on-bottom holds the invert; flat-on-top holds the crown; concentric holds the centerlinefitting practice