Why Accommodating Pressure Thrust Is Crucial In Designing A Quality Metal Bellows

For any plant engineer who oversees the operation of piping or duct systems, the issue of pressure is a significant concern. Pressure and temperature go hand in hand: as thermal stress increases in the gas passing through the ductwork, so do pressure forces increase with the expanded media volume. Pressure therefore represents a fundamental physics variable when considering the engineering specifications for any high temperature gas transfer application.

This also makes the issue of pressure thrust a primary focus when FlexCom engineers consider the specific needs for a client's metal expansion joint design. "Pressure thrust" refers to the forces created by high pressure that tend to drive the joint endpoints and duct flanges to move away from each other. A properly designed metal bellows must not only resist pressure thrust, it must do so while still allowing the joint certain degrees of axial, lateral or angular movement, as well as accommodation for other thermal effects.

FlexCom engineers have a wide variety of options available for properly engineering a metal bellows to meet the specific requirements presented by even the most demanding industrial applications. These include:

• Selecting the right joint design. FlexCom metal bellows come in a variety of general designs, each one appropriate to a specific balance of pressure, thermal expansion and movement compensation engineering requirements. Whether your needs can be met by a simple unrestrained Universal bellows, or you require something more sophisticated (such as a Gimbal or Slotted Hinged joint design), selecting the right design for the job is always our first consideration when fabricating your metal expansion joint.


• Varying the bellows size. Often the simplest way to accommodate the stress of high pressure flows is simply to increase the diameter of the duct. While the expansion joint designer has little control over the client's ductwork size specifications, we do commonly fabricate metal bellows for ducts and pipelines of all diameters and size configurations.


• Altering the bellows spring rate. Spring rate is essentially a measure of the bellows' flexibility. By making the joint more or less flexible (by varying metal grades, opting for multi-ply steel fabrication or simply selecting a different overall design), adjusting the spring rate can be useful for calibrating the joint design to meet very specific engineering requirements.


• Adding tie rods and/or other external protection. Not to be confused with control or limit rods (which limit joint movement range, but are not meant to absorb pressure thrust), tie rods may be included in some metal bellows designs to protect the joint from lateral pressure thrust forces. While tie rods aren't appropriate to every metal bellows design, they commonly represent the workhorse option for high pressure applications - the heavy duty design addition for joints intended for high pressure, high temperature plant systems.

An improperly designed metal bellows represents more than a threat to efficiency: it can form a single point of failure in your plant application. A metal bellows precisely engineered to counter issues such as pressure thrust, on the other hand, contributes to greater system predictability, longer plant uptime and reduced maintenance costs. That alone should be reason enough to make sure that your metal expansion joint is built to specification - with a quality design built to last.

Learn more about how FlexCom metal bellows are designed to meet even the most exacting engineering specifications, delivering exceptional performance in high pressure gas and liquid transfer applications.

In this metal expansion joint design, two stainless steel bellows are separated by a pipe spool included to allow for lateral movement under high temperature and high pressure conditions. The Tied Universal joint body is then fitted with external tie rods, fabricated from heavy duty stainless steel, in order to absorb pressure thrust forces as well as offer a degree of travel limit to the joint itself. The tie rods themselves, typically maintaining temperatures at or near ambient temperature, do not expand or contract with thermal changes in the transfer media. This makes a Tied Universal metal bellows an exceptional solution for high pressure systems requiring only lateral movement compensation.

Would you like to learn more about FlexCom metal bellows configurations? Come visit us at www.flexcomonline.com - or request a quote today for specific information about your own expansion joint needs!

Are you in search of a truly superior expansion joint for your industrial engineering needs? CLICK HERE to contact us today and request a quote!

FlexCom Inc. 6864 Chrisphalt Drive Bath, PA 18014 Phone: 610-837-3812 Toll Free: 888-376-FLEX

• Pressure Thrust and Metal Bellows Expansion Joint Design
• Our Products: Tied Universal Metal Expansion Joints
• About FlexCom Inc.

FlexCom Composite Flat Belts.
Made With ChemShield®.

FlexCom® fabric and composite expansion joints are constructed of ChemShield®, a composite material designed to provide maximum strength and protection for tough environmental conditions.

ChemShield® is a PTFE-coated, high strength fiberglass cloth, which is in turn laminated to a sheet of 100% PTFE fabric - making FlexCom fabric expansion joints an ideal solution for any gas transfer application that must withstand heavy thermal stress.

We've Moved!

Since 1991, Flexible Compensators (FlexCom) Inc. has focused its energy and resources upon the single task of becoming the industry leader in robust, dependable fabric and metal expansion joints. In 2008 we took the next logical step: moving into a new state of the art manufacturing plant. Our new plant in Bath, Pennsylvania today serves as our fully integrated and full service engineering, manufacturing and test facility.

Two-thirds larger than our previous plant, this new facility has effectively doubled FlexCom's production capacity, enabling us to offer even greater cost efficiency, quality control, fast shipping and customer service.