The dimensions of a reducer mainly include four key parameters: nominal diameter (large end / small end), length, taper angle, and wall thickness, in accordance with standards such as GB/T (Chinese) and ASME (American). Clear standard dimensions are specified for different types (concentric / eccentric) and sizes of reducers, as detailed below:
I. Definition of Core Dimension Parameters
1. Nominal Diameter (DN / NPS)
- Marking format: Nominal diameter of large end × Nominal diameter of small end (e.g., DN200×DN150, 4″×2″), representing the pipe sizes to be connected at both ends.
- Common specification ranges:
- Metric: DN15×DN10 ~ DN1200×DN600 (small-end diameter ≥ 1/2 of large-end diameter; e.g., DN100 matches a minimum of DN50 to avoid excessive taper angle).
- American standard: 1/2″×1/4″ ~ 48″×24″ (marked in NPS inches; corresponding to metric DN: 1″ = DN25, 4″ = DN100).
2. Length (L)
- Definition: Total axial length of the reducer (distance from large-end face to small-end face), determined by taper angle and diameter difference.
- Default taper angle in GB / ASME: 15°~30° (smaller taper angle means longer length and lower flow resistance).
- Eccentric reducers have the same length as concentric reducers of the same specification, differing only in axis offset (offset = large-end radius − small-end radius).
3. Taper Angle (θ)
- Concentric reducers: Taper angle is typically 15°, 20°, or 30° (20° recommended by GB); custom angles from 5° to 45° are available for special requirements.
- Eccentric reducers: Same taper angle as concentric reducers, with a flat-bottom design (bottom of small end aligned with bottom of large end).
4. Wall Thickness (t)
- Linked to pressure rating (PN / Class / Sch); large-end wall thickness ≥ small-end wall thickness (due to larger pressure-bearing area at the large end).
- Example (DN200×DN100, carbon steel):
- PN1.6 / Sch40: Large-end wall thickness 6.0 mm, small-end wall thickness 4.5 mm.
- PN4.0 / Sch80: Large-end wall thickness 8.0 mm, small-end wall thickness 6.0 mm.
II. Dimension Standards (GB & ASME)
1. Chinese Standard (GB/T 12459-2017)
- Applicable: Steel butt-weld concentric / eccentric reducers.
- Key provisions:
- Length formula: L=2×tan(θ/2)D−d(D = outer diameter of large end, d = outer diameter of small end, θ = taper angle).
- Outer diameter tolerance: ±0.5 mm for DN ≤ 100; ±1% for DN ＞ 100.
- Length tolerance: ±5 mm.
2. American Standard (ASME B16.9-2020)
- Applicable: Factory-made forged steel butt-weld reducers.
- Key provisions:
- Long-radius reducer (default): Length L=3×(D−d).
- Short-radius reducer (custom): Length L=1.5×(D−d).
- Wall thickness follows Sch ratings (Sch40 / Sch80, etc.), complying with ASME B36.10M.
III. Dimension Differences Between Types
1. Concentric Reducer
- Structure: Coaxial at both ends, symmetrical cone.
- Dimensional features: Uniform length, wall thickness tapering (or stepped) from large end to small end.
- Example: DN100×DN50 concentric reducer, large-end OD 114.3 mm, small-end OD 57 mm, length L = 140 mm, taper angle 20°.
2. Eccentric Reducer
- Structure: Parallel offset axes (offset = 28.65 mm for DN100×DN50), flat-bottomed.
- Dimensional features: Same length and taper angle as concentric reducers; only bottom aligned, top sloped.
- Example: DN100×DN50 eccentric reducer, distance from large-end bottom to small-end bottom = 0 (aligned), distance from large-end top to small-end top = 140 mm.
IV. Dimensions of Plastic Reducers (PVC / PPR / PE)
- Marking: De (outer diameter) × De (e.g., De110×De75); uses outer diameter directly instead of nominal DN.
- Length: Short type (50~100 mm, socket connection), long type (150~300 mm, fusion connection).
- Wall thickness: Rated by SDR (e.g., SDR11 De110×De75, large-end wall thickness 10.0 mm, small-end wall thickness 6.6 mm).
V. Dimension Inspection Requirements
- Nominal diameter: Measure outer diameters at both ends with calipers; deviation ≤ ±1%.
- Length: Measure with tape measure / total station; deviation ≤ ±5 mm.
- Taper angle: Measure with protractor; deviation ≤ ±1°.
- Wall thickness: Measure three points (large end, small end, middle) with ultrasonic thickness gauge; deviation ≤ ±12.5%.
VI. Typical Dimension Marking Examples
- GB concentric reducer: DN200×DN150 PN2.5 L=280mm 20#(Large end DN200, small end DN150, pressure rating PN2.5, length 280 mm, carbon steel).
- ASME eccentric reducer: 4″×2″ Class300 Sch80 L=140mm ASTM A234 WPB(4″=DN100, 2″=DN50, pressure rating Class300, wall thickness Sch80, length 140 mm, carbon steel).
- Plastic reducer: De110×De75 SDR11 PE100(PE material, outer diameter 110 mm to 75 mm, SDR11 rating).
