When large amounts of axial deflection are required in piping systems of relatively high pressure, bellows which are internally pressurized have limitations due to the phenomenon called squirm. The X-Flex type expansion joint, in which the bellows elements are arranged so that they are exposed to the media on their external surface, and are therefore externally pressurized, is an ideal unit. As discussed in more detail in the X-Flex section of this catalog, externally pressurizing a bellows eliminates squirm as a limitation to the design and permits the safe acceptance of large amounts of axial thermal expansion. This type of expansion joint has many other inherent advantages over internally pressurized bellows. Please refer to the Safety Recommendation section as well as the X-Flex discussion.