Expansion Joints - Type MPBI Inline pressure balanced | Macoga

Macoga MPBI Inline Pressure Balanced Expansion Joints

Macoga MPBI are metallic inline pressure balanced expansion joints designed for straight pipeline sections. The assembly absorbs axial or lateral movements while minimizing the transmission of pressure thrust to piping, pumps, turbines, or other sensitive equipment.

Operating Principle

The construction includes a main line bellows and an additional balancing bellows, both exposed to the same operating pressure. The opposing forces are counteracted via tie rods, neutralizing pressure thrust within the unit. As a result, only intermediate anchors are required in the piping system; main anchors for pressure thrust are not necessary.

Permissible Movements

• Axial movement: primary use in straight runs.
• Lateral movement: in one or more planes, depending on design.
• Angular movement: only if specified, e.g., with dual tie rods.
• Torsion: must not be imposed on the bellows.

Typical Applications

Used in steam, hot water, thermal oil, process gases, compressor lines, turbines, heat exchangers, and equipment where allowable nozzle loads are limited. Selection is based on DN, pressure class, temperature, axial/lateral travel, cycle life, bellows material, and media compatibility. Units are manufactured to EN, ASME, or customer specifications.

MPBI vs MWA / MWT

• MWA: unrestrained; requires main anchors to absorb pressure thrust.
• MWT: tied; limits thrust but alters movement characteristics.
• MPBI: pressure balanced; suitable where expansion must be absorbed without transferring thrust to adjacent equipment.

Installation and Inspection

Not intended for misalignment correction. Prior to installation, verify nameplate data, flow direction (with internal sleeve), guides, intermediate anchors, and bellows cleanliness. Remove yellow shipping bars before pressure testing. For hydrostatic tests, use chloride-free water.

FAQ

Is an actuator required?
No. This is a passive piping component.

When is it selected?
When thermal movement must be absorbed in a straight run without imposing pressure thrust on equipment nozzles.