There are certain expansion joint applications that call for large axial movements. These are frequently encountered in steam distribution systems found in hospital, schools, or military installations. Internally pressurized assemblies become unstable even at low pressures when the number of convolutions reaches a certain limit; therefore, the problems created by these requirements cannot be solved using a Single Bellows Assembly. (Under increasing pressure, an internally pressurized bellows will act as an unstable column in compression, and squirm.) In cases like these, an Externally Pressurized Assembly provides the most viable solution. When pressure is applied externally to the bellows, as shown in the figure 1, the bellows are placed in tension. In this condition squirm is not a factor. A greater number of convolutions can be added to the bellows even at higher pressures, resulting in increased movement capability. This style joint has the added benefit of self-draining convolutions. All the trapped liquid media can be purged from the outer casing eliminating the possibility of liquid "flashing" to vapor.

An anchor foot can be added to the Single Externally Pressurized Style allowing it to act as an intermediate anchor. The anchor foot is designed to withstand any loads produced by the deflection of the bellows. Dual Style Externally Pressurized designs are equipped with an anchor foot as a standard. The internal and external rings on both styles act as a pipe guide so the first guide (G1) is not necessary.

• Bellows protection
• Smooth flow
• Oversize bellows
• Drain connection
• Purge connection
• Fail-safe design
• Self-draining convolutions
• Joint acts as first guide