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The Bellows Expansion
WinPride | Updated: Sep 30, 2017

Bellows Expansion Joints are great for accommodating axial, lateral and angular movements for a wide array of piping applications. Some applications may contain high flow velocities, which can induce severe vibration and lead to premature failure to the bellows element. The way to address this is to utilize a bellows expansion joint containing an internal sleeve, also known as a flow liner.

A flow liner within a bellows expansion joint protects the integrity of the bellows element by redirecting the media (air, gas, steam, water, etc.) away from flowing directly over the bellows convolutions as it passes through. It makes sense, seems simple and as DME uses EJMA as a standard in manufacturing, here is what recommends:

EJMA 9th Edition, Section 4.10

Internal Sleeves shall be specified for ALL expansion joints in the following cases:

a. When it is necessary to hold friction losses to a minimum and smooth flow is desired.
b. When flow velocities are high and could produce resonant vibration of the bellows. Internal sleeves are recommended when flow velocities exceed the following values:
Air, Steam and other Gases
Up to 6 in. diameter – 4 ft./sec./inch of diameter.
Over 6 in. diameter – 25 ft./sec
Water and other Liquids
Up to 6 in. diameter – 2 ft./sec./inch of diameter
Over 6 in. diameter – 10 ft./sec.

There are several other things to consider when choosing whether or not to use a flow liner. Due to lateral movements, the gap between the bellows and the internal sleeve must be designed appropriately in order to prevent contact or binding against the inside diameter of the pipe or fitting. Also, making sure the inside diameter of the internal sleeve does not create back pressure or restrict the flow of media is extremely important, and usually can be avoided by utilizing an oversize bellows.

Abrasive media such as a catalyst or ash will erode or destroy the bellows element, so it is recommended the internal sleeve is of a heavy gauge. A thicker liner is also recommended where turbulent flow is generated within ten pipe diameters of the expansion joint by changes in flow direction, valves, cyclonic devices, a tee or an elbow.

Paying attention to applications where flow liners should be used is important. Any question of whether or not one is needed can be quickly resolved by contacting DME, we do it everyday.


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