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How to Install Union Type Rubber Flexible Joints (Union Rubber Bellows)

Installing Union Rubber Expansion Joints properly is important to ensure maximum flexibility, leak-free operation, and long service life in pipelines.

 

1. Tools & Materials Needed

• Union type rubber flexible joint (correct size & pressure rating)
• Pipe wrenches or adjustable spanners
• PTFE tape or thread sealant (if required)
• Pipe supports or hangers
• Alignment tools (spirit level, straight edge)
• Torque wrench (for controlled tightening)
• Safety gloves, safety glasses, PPE

 

2. Pre-Installation Checks

✅ Inspect the rubber bellows for cracks, cuts, or storage damage.
✅ Check that the union ends (threaded / flanged) are clean and free from rust, burrs, or welding slag.
✅ Verify the pipe size, pressure rating, and rubber material (EPDM, NBR, Neoprene, Viton, etc.) matches your system.
✅ Ensure proper spacing is allowed for expansion and movement.
✅ Pipes must be properly supported — rubber joints should not carry the pipeline weight.

 

3. Installation Steps (Threaded Union Type)

1. Pipe Alignment:
   • Ensure both connecting pipes are properly aligned before inserting the joint.
   • Rubber bellows are not designed to correct major misalignment (only minor deviations).
2. Apply Sealant:
   • Wrap PTFE tape (Teflon tape) or apply thread sealant on the male threaded pipe end.
3. Insert the Joint:
   • Position the union type rubber joint between the two pipe ends.
4. Tighten Union Nuts:
   • Hand-tighten first to ensure even threading.
   • Use pipe wrench/spanner to tighten firmly, but do not over-tighten (over-compression can damage the rubber).
5. Check Orientation:
   • The expansion joint should be installed vertically or horizontally depending on the system design.
   • Ensure there is no twisting or torsion stress on the bellows.
6. Pipe Supports:
   • Install pipe supports or hangers near the joint to avoid pipeline load stress.
   • Expansion joints should only absorb movement, not hold the pipeline weight.
7. Final Tightening:
   • Use torque wrench (if specified) to apply correct torque according to manufacturer’s recommendation.

 

4. Installation Steps (Flanged Union Type)

1. Align the pipeline flanges accurately.
2. Place gasket (if required) between flange faces.
3. Insert the union type rubber joint in position.
4. Insert bolts through flange holes.
5. Tighten bolts gradually in a cross/star pattern to ensure even compression.
6. Do not overtighten — excessive pressure will shorten bellow life.

 

5. Post-Installation Checks

✅ Visually inspect for any twisting, stretching, or uneven compression.
✅ Make sure there is no direct contact with sharp objects that may cut the rubber.
✅ Verify that thermal expansion allowance is considered (bellows must not be pre-stretched or compressed at rest).
✅ Slowly pressurize the system and check for leaks.
✅ Retighten bolts/nuts after initial pressurization if required.

 

6. Maintenance & Safety Tips

• Do not paint over rubber bellows (paint chemicals may damage rubber).
• Keep away from ozone sources (high-voltage equipment) that can age rubber.
• Inspect regularly for cracks, swelling, or wear.
• Replace immediately if rubber deterioration or leakage is observed.
• Store spare joints in a cool, dry place, away from sunlight.