Basic information about Expansion Joint

Basic information about Expansion Joint

expansion joint

What is an Expansion Joint?

It is an elastic element that allows the independent movement of its two ends or flanges, avoiding the transmission of displacements or undesirable or unwanted movements in the installation.

They are flexible accessories that are mounted in the pipes to absorb the movements caused by thermal expansion and / or mechanical vibration. The thermal expansion generates in a pipe system, movements in different directions, this caused that different expansion joints were developed to absorb these movements or some combination of them.

Additionally it can be defined as a flexible element, formed by one or more waves / arcs, designed to withstand the internal pressure of a given fluid at the working temperature, but flexible enough to absorb the movements that arise.

What type of movement absorbs an expansion joint?

  • Lateral: the two flanges move in parallel planes.
  • Axial (compression and extension): its two flanges move along the axis of the expansion joint. The movement can be positive (extension) or negative (compression).
  • Angular: one of the flanges moves at an angle to the other.
  • Rotational: one of the flanges rotates with respect to the other.

NOTE: Not all expansion joints are capable of absorbing all movements (case of rotation in metal joints) and there are movements that can not be absorbed at the same time.

Why use expansion joint?

In a pipe system, various methods can be applied to absorb the stresses produced by thermal movements (axial, lateral and / or angular), vibrations, land settlements, assembly misalignments, etc. Within the existing methods (flexibility of the layout of the piping system, lira or loops, sliding joints and expansion joints), the most preferred by the designers of piping systems is the expansion joint, because, for the same application, requires less space.

Types of Expansion Board

Depending on the construction material, there are 3 main categories:

  • Tissue.
  • Rubber.
  • Metal.

How should they be used?

Depending on the design of the pipe system, a joint will be of the “non-restricted” type or the “restricted” type

If they are “non-restricted” you need a perfect location of the anchors and the guides for their proper functioning, since under the effect of the pressure a longitudinal effort is exerted in both directions to the expansion joint that must be resisted by the system.

If they are “restricted” (tie rods, joints, etc.) only light supports are needed which, in addition to the external loads (weight, wind, etc.), resist the forces of activation of the expansion joint and the friction forces in the guide supports.

What is the activation force and how does the installation affect it?

In an expansion joint, the activation force is defined as the minimum energy necessary to produce a deformation, whether axial compression or extension, lateral or rotation.

This means that an expansion joint with a low activation force begins to deform before one with a high activation force. In other words, a compensator with a low activation force decreases the stresses that the pipe system must support. This data is of great value in pipes made of plastic materials that present fragility in the area of the flanges.

Advantages of using an expansion joint with a low activation force:

  • Best functional guarantee for a pipe installation.
  • Lower manufacturing costs since the pipes can have a lower reinforcement thickness.
  • Lower maintenance costs for the installation, since fewer requirements are applied to the structure.
  • Longer useful life for the support systems to work with less load effort.

In Plumbing Products Spec LLC we have the support of recognized brands in pipes of the Thermal, Vibration, Noise and Seismic segments.

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