by Lloyd Aanonsen (FSA Member)
July 23, 2015

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In-line pressure-balanced rubber expansion joints provide the only effective solution for directly absorbing large axial thermal movements while continuously self-restraining the pressure thrust forces. This arrangement consists of tie devices interconnecting the main joint sections to the opposing balancing joint section and is commonly used when the support structure or adjacent equipment have load limitations. The body is often a one-piece rubber construction with full rubber flanges; a high-grade, leak-proof tube; multiple layers of high-strength tire cord; high-tensile steel reinforcement; a seamless cover and galvanized retaining rings. The economic benefits of using pressure-balanced designs include a smaller system footprint as well as far fewer guides, anchors and supports.

Figure 4. Two gimbal REJs in a multiple-plane, Z-shaped pipe runFigure 4. Two gimbal REJs in a multiple-plane, Z-shaped pipe run

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Elbow pressure-balanced rubber expansion joints are designed to absorb all directional movement while continuously self-restraining the pressure thrust forces. This consists of tie devices interconnecting its main joint section to its opposing balancing joint section and is often used when the support structure or adjacent equipment have load limitations.

The pair of spool-type bodies are often constructed with full rubber flanges; high-grade, leak-proof tubes; multiple layers of high-strength tire cord; high-tensile steel reinforcements; seamless covers and galvanized retaining rings. The economic benefits of using pressure-balanced designs include a smaller system footprint as well as far fewer guides, anchors and supports.

Figure 5. In-line pressure-balanced REJ in straight pipe run with load limitationsFigure 5. In-line pressure-balanced REJ in straight pipe run with load limitations

To determine which style of REJ to use, divide the proposed piping into individual sections (straight runs, L- or Z-shaped bends) by choosing tentative anchor locations. Each section can then be optimized by taking advantage of each REJ's specific capabilities and later incorporated into the complete piping system.

Figure 6. Elbow pressure-balanced REJ in a single-plane, L-shaped pipe run with load limitationsFigure 6. Elbow pressure-balanced REJ in a single-plane, L-shaped pipe run with load limitations

This sometimes iterative approach requires additional design considerations for the following:

  • Capabilities and limitations of different anchor types including main, directional or intermediate
  • Piping codes i.e., American Society of Mechanical Engineers (ASME) B31.1, ASME B31.3 or others
  • Location of various equipment, branch connections and space restrictions
  • Capabilities of support structures and load limitations on piping and equipment
  • Operating conditions including, but not limited to, temperature and pressure
  • Amount of thermal and/or external movements anticipated
  • Need to absorb noise and vibration
  • Need to compensate for misalignment
  • Need to provide access to piping and equipment
  • Need to absorb shock loads and required cycle life
  • Capabilities and limitations of different REJ styles including unrestrained and restrained arrangements

In many cases, multiple solutions are possible depending on owner preference. Contact an FSA manufacturer for further consultation and design review.

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