HDPE Eccentric Reducer is one of the key fittings in polyethylene piping networks. When reducing the pipe diameter or connecting to a smaller size, it keeps one side of the pipe aligned, preventing air pockets, water hammer, and flow instability.
What is a polyethylene eccentric reducer?
An eccentric reducer is a fitting with two bores that are parallel but have different centers, so one side of the connection remains “flat.” It is used where the bottom of pipe (B.O.P) must stay at a constant elevation. This design eliminates air‐trap cavities and reduces flow turbulence during the diameter change.
Operation and difference from a concentric reducer
- In an eccentric reducer, the diameter change occurs on the top side of the flow path while the bottom side is kept level; the visible step height equals the difference between the two pipe diameters.
- Unlike a concentric reducer, which is conical and fully coaxial, the eccentric type has one flat face for alignment with the pipeline.
- On pump suction lines, using an eccentric reducer prevents air from accumulating in the pipe and entering the impeller, directly mitigating cavitation and vibration.
Advantages and applications
- Maintains pipe invert level and prevents air pockets in horizontal runs and pump suction lines
- Reduces local head losses caused by turbulence at the diameter transition
- Suitable for water transmission, wastewater, irrigation, mining, and process industries
- Compatible with underground installation thanks to HDPE’s flexibility and resistance to impact and corrosion
Correct joining and installation methods
- Butt Fusion: The common method for injection-molded HDPE reducers. Surfaces must be clean, aligned, and oxide-free; welding pressure and temperature should be set according to wall thickness (SDR).
- Orientation to flow: Place the reducer’s flat face so the pipe invert remains level, avoiding an air-trap void at the top.
- Distance to pump: On pump suction, install the reducer as close as possible to the suction flange and avoid sharp elbows upstream.
- Weld quality control: Check for uniform bead, alignment, and absence of a step at the pipe-to-reducer transition, then perform a hydrostatic test.
Technical selection guide
- Material grade: PE100 is recommended over PE80 for higher pressures due to greater mechanical strength.
- Pressure class/SDR: Match the reducer’s nominal pressure (PN) and SDR to the pipe to prevent steps and stress concentration at the joint.
- Fluid and temperature: Suitable for potable water, wastewater, and non-corrosive industrial fluids. Apply pressure derating factors at elevated temperatures.
Quick selection table for pressure class
| Material grade | Recommended SDR | Nominal pressure (approx.) | Recommended jointing | Example application |
|---|---|---|---|---|
| PE100 | SDR11 | PN16 | Butt fusion | Urban/industrial water supply |
| PE100 | SDR17 | PN10 | Butt fusion | Irrigation & gravity–pressure lines |
| PE80 | SDR11 | PN12.5 | Butt fusion | Light & secondary irrigation |
| PE100 | SDR9 | PN20 | Butt fusion | Pump suction/discharge & higher pressures |
Note: In every project, manufacturer specifications and construction drawings are the final reference; this table is only an initial selection guide.
Dimensional referencing: L1, Lt and L2
A polyethylene eccentric reducer has three reference lengths:
- Lt: overall reducer length
- L1: length of the larger end
- L2: length of the smaller end
These parameters are used to ensure alignment, plan installation space, and verify dimensional quality upon receipt.
Nominal size table for polyethylene eccentric reducers (mm)
| Nominal size | Lt | L2 | L1 |
|---|---|---|---|
| 50×90 | 150 | 35 | 50 |
| 63×90 | 150 | 35 | 50 |
| 75×90 | 150 | 35 | 50 |
| 50×110 | 150 | 35 | 50 |
| 63×110 | 150 | 35 | 50 |
| 75×110 | 150 | 35 | 50 |
| 90×110 | 150 | 35 | 50 |
| 63×125 | 150 | 35 | 50 |
| 75×125 | 150 | 35 | 50 |
| 90×125 | 150 | 35 | 50 |
| 110×125 | 150 | 35 | 50 |
| 90×160 | 180 | 35 | 50 |
| 110×160 | 180 | 35 | 50 |
| 125×160 | 180 | 35 | 50 |
| 140×160 | 180 | 35 | 50 |
| 90×180 | 180 | 35 | 50 |
| 110×180 | 180 | 35 | 50 |
| 125×180 | 180 | 35 | 50 |
| 140×180 | 180 | 35 | 50 |
| 160×180 | 180 | 35 | 50 |
| 110×200 | 185 | 40 | 50 |
| 125×200 | 185 | 40 | 50 |
| 140×200 | 185 | 40 | 50 |
| 160×200 | 185 | 40 | 50 |
| 180×200 | 185 | 40 | 50 |
| 110×225 | 185 | 40 | 50 |
| 125×225 | 185 | 40 | 50 |
| 140×225 | 185 | 40 | 50 |
| 160×225 | 185 | 40 | 50 |
| 180×225 | 185 | 40 | 50 |
| 200×225 | 185 | 40 | 50 |
| 140×250 | 185 | 40 | 50 |
| 160×250 | 205 | 40 | 50 |
| 180×250 | 205 | 40 | 50 |
| 200×250 | 205 | 40 | 50 |
| 225×250 | 205 | 40 | 50 |
| 200×315 | 220 | 40 | 50 |
| 225×315 | 220 | 40 | 50 |
| 250×315 | 220 | 40 | 50 |
| 200×355 | 220 | 40 | 50 |
| 225×355 | 220 | 40 | 50 |
| 250×355 | 220 | 40 | 50 |
| 315×355 | 220 | 40 | 50 |
| 200×400 | 220 | 40 | 50 |
| 225×400 | 220 | 40 | 50 |
| 250×400 | 220 | 40 | 50 |
| 315×400 | 220 | 40 | 50 |
| 355×400 | 220 | 40 | 50 |
Common errors and remedies
- Mismatch of PN/SDR between reducer and pipe: causes a step and stress concentration at the weld; select matching ratings.
- Misalignment during welding: leads to uneven flow and higher loss; use proper jigs and check the weld bead.
- Incorrect orientation: can create an air-trap space; position the flat side to keep the pipe invert level.
- Ignoring temperature conditions: adjust welding parameters and cooling time in cold or hot weather.
Tamam Baha supplies a range of polyethylene fittings—including eccentric reducers—in PE80 and PE100 grades and various pressure classes. The team provides technical guidance on size, SDR, and installation, with custom supply to project drawings and dimensional QC (L1, L2, Lt). Please note Tamam Baha is one of several sellers of this brand in the Iranian market and does not hold exclusive rights.
