Control Units

Control Units

Control units may provide additional support to rubber expansion joints by adding rigidity strength when proper anchoring is not available. Control units are also used to restrict the movement allowances of an expansion joint. They should always be used when excessive stress and motion on the joint might cause that joint to fail or be over-stressed to the point of near failure of the joint and its reason for being. Control units are made up of:

  • Gusset Plates: Triangular shaped plates of steel that attach to the bolt circle of the flange and provide for a threaded rod at the apex.
  • Threaded Rod: a fully threaded steel rod installed at the top of the gusset plate to give strength and rigidity to the rubber expansion joint.
  • Nuts: The threaded rod is secured to the gusset with nuts placed along the outer face of the gusset typical installation has two (2) nuts outside of each gusset plate
  • Internal Nuts: One method of restricting the compression of an expansion joint is by applying two (2) nuts to the inside of the gusset plate to limit how far the gusset can travel along the axis.
  • Compression Rod: A tubular section of steel pipe installed around the threaded rod on the inside of the gusset plates to limit the allowable compression movement.

Control units may be required to limit both extension and compression movements.

Control units must be used when it is not feasible in a given structure to provide Control Unit adequate anchors in the proper location. In such cases, the static pressure thrust of the system will cause the expansion joint to extend to the limit set by the control rods which will then preclude the possibility of further motion that would over-elongate the joint. Despite the limiting action that control rods have on the joint, they must be used when proper anchoring cannot be provided.

Pipe sleeves or inside nuts can be installed on the control rods. The purpose of the sleeve is to prevent excessive compression in the expansion joint. The length of this pipe sleeve should be such that the expansion joint cannot be compressed beyond the maximum allowable compression.

The exact number of control rods (see control unit dimensions table) should be selected on the basis of the actual design/test pressure of the system. Always specify the mating flange thickness when ordering control unit assemblies.

The number of control rods installed on a joint is dictated by the pressure requirements on the system. The number of rods can also give greater control over any lateral movements.

A. Assemble expansion joint between pipe hubs to the manufactured face-to-face length of the expansion joint.

B. Assemble control rod plates behind pipe hubs. Flange bolts through the control rod plate must be longer to accommodate the plate. Control rod plates should be equally spaced around the flange. Depending upon the size and pressure rating of the system, 2, 3 or more control rods may be required.

C. Insert control rods through top plate holes. Steel washers are to be positioned at the outer plate surface. An optional rubber washer is positioned between the steel washer and the outer plate surface.

D. If a single nut per unit is furnished, position this not so that there is a gap between the nut and the steel washer. This gap is equal to the joint’s maximum extension (commencing with the nominal face-to-face length). To lock this nut in position, either “stake” the thread in two places or tack weld the nut to the rod. If two jam nuts are furnished for each unit, tighten the two nuts together, so as to achieve a “jamming” effect to prevent loosening.

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