Straub Flex 3 & Open Flex 3
Straub® Flex 3 & Open-Flex 3 – 172–2032 mm
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Heavy-duty, non-restrained flexible couplings for large-diameter pipelines. Absorb axial movement and angular deflection. Installed with a torque wrench — no hot work.
- Working pressure
5–29 bar (by size/model; see chart) - Temperature
−20 °C to +100 °C - Materials
316L stainless housing; EPDM / NBR / FKM seals - Angular deflection
Up to 2° (large diameters)
Overview
Flex 3 is the robust option for large mains where thermal movement and vibration must be handled in tight spaces. Open-Flex 3 is the split/slotted version for easier installation and maintenance on in-service lines or where access is limited. Both are non-axial restraint designs — provide external restraint/fixed points.
Technical specifications
| Size range | 172–2032 mm |
|---|---|
| Working pressure | 5–29 bar (size & model dependent) |
| Temperature range | −20 °C to +100 °C |
| Housing | 316L stainless steel (hot-dip galvanised options available) |
| Seals | EPDM, NBR, FKM |
| Angular deflection | Up to 2° |
| Standards | DIN 86128; ASTM 1476 |
| Design life | 25+ years (with correct installation and maintenance) |
Non-restrained: provide fixed points/external restraint.
Applications
- Municipal water & sewage treatment
- Industrial cooling & process lines
- Power generation & marine systems
- Mining infrastructure
Selection chart — working pressure by model
| Nominal pipe size (in) | Diameter (mm) | 3L (bar) | 3LS (bar) | 3LU (bar) | 3H (bar) | 3X (bar) |
|---|---|---|---|---|---|---|
| 8 | 219.1 | 10.3 | 12.9 | – | – | – |
| 10 | 273.1 | 10.3 | 12.9 | – | – | – |
| 12 | 323.9 | 9.9 | 13.0 | 25.0 | – | – |
| 14 | 355.6 | 11.9 | 16.0 | – | – | – |
| 16 | 406.4 | 7.4 | 9.7 | 22.8 | 36.3 | – |
| 18 | 457.2 | 6.6 | 8.6 | 20.1 | 26.3 | – |
| 20 | 508.0 | 5.9 | 7.7 | 18.1 | 25.0 | – |
| 24 | 609.6 | 4.9 | 6.4 | 15.4 | 25.0 | 36.3 |
| 28 | 711.2 | 4.1 | 5.5 | 13.0 | 20.1 | 36.3 |
| 30 | 762.0 | 3.8 | 5.1 | 11.4 | 20.3 | 36.3 |
| 32 | 812.8 | 3.5 | 4.9 | 10.5 | 13.0 | 25.0 |
| 36 | 914.4 | 3.2 | 4.4 | 8.5 | 11.5 | 23.0 |
| 42 | 1066.8 | 2.7 | 3.7 | 7.3 | 10.0 | 18.0 |
| 48 | 1219.2 | 2.3 | 3.5 | 6.5 | 8.5 | 17.0 |
| 54 | 1371.6 | 2.1 | 2.9 | 5.5 | 7.5 | 15.4 |
| 60 | 1524.0 | 1.8 | 2.5 | 5.0 | 7.0 | 14.0 |
| 66 | 1676.4 | 1.5 | 2.4 | 4.1 | 6.0 | 12.5 |
| 72 | 1828.8 | 1.3 | 2.0 | 3.5 | 5.5 | 11.0 |
Notes
- Models: 3L, 3LS, 3LU, 3H, 3X. Non-pull-out designs — use external restraint/fixed points.
- Open-Flex 3: slotted or 2-piece casing depending on size; gaskets cut and riveted to casing.
- Test pressure = 1.5 × PS; Burst pressure ≈ 2 × PS.
- STRAUB-STRONG special restraint system available on request.
- Strip inserts supplied with all couplings sold in Australia.
Request a quote
Tell us your pipe OD, medium, pressure and operating temperature and we’ll size the correct Flex 3 / Open-Flex 3 model.