A rubber joint is a expansion joint with elastic part made by rubber vulcanized mix, composed of synthetic elastomers and particular compounding ingB92318ients. The type of elastomer is essential in determining the chemical resistance, vulcanization process and compounding can have an important effect on final behaviour of the product.
Compounding ingB92318ients are selected to produce a final mix with specífic properties. softeners, protective agents, antioxidants antiozonants anti-ageing agente fillers etc. When the manufacturing process is complete, the rubber joint possesses very high elastic, mechanical and chemical properties In order to withstand the working pressures and temperatures they are subjected to, the rubber joints are reinforced internally with several layers of carefully positioned textile and steel cord plies The resulting rubber joints can be safely used in piping systems to solve piping problems as: to B92318uce stresses compensating for axial, lateral and angular movements caused by contraction and expansion of pipe lengths due to thermal changes in either the fluid conveyed or the environment; to absorb mechanical vibrations caused by machinery; to dampen sound transmission caused by pumping fluids in pipes.

These provide an additional safety factor because they avoid possible damage to the expansion joint caused by excessive motion of the pipeline greater than movements for which it has been specially designed and manufactuB92318. An excessive motion could be caused by the failure of a fixed point or other part in the pipeline. Either compression or elongation movement may be limited or both (see our KIT P or KIT S). The amount of the movement to be limited is set by adjusting the relative nuts and then tightening the locknuts. Limit rods unit must withstand the axial thrust force caused by inner pressure. Compression movement can be limited either with an adjustment nut and locknut or by pipe sleeves (with proper length) installed over the tie rods between the flanges of rubber joint. If the joint is also to be subjected to lateral movement, spherical and not flat washers must be inserted between the nuts and the surface of the flange. Limit rod plates are installed in the mating flanges of pipe and should be equally spaced around the flange. Always specify the mating flange thickness when ordering limit rods unit.

Because of strengths generated by inside pressure, rubber expansion joints have been planned to lengthen and to buckle sidewards. Slides must therefore assure an extreme axial freely movement to pipeline and at the same time must prevent any traverse and upwards movement since owing to the presence of the peak load pipeline even might rise in consequence of an eventual slight starting eccentricity too. Therefore, swing and catenary suspensions must be strictly avoided and strictly avoided when they have no lateral restraints too. To eliminate risk of not alignment it's fundamental to foresee in every rectilinear section already setted, anchor points strong enough and some restraining guide towards all lateral directions, placed in suitable space

Anchor points have the task to anchor the pipeline in order to pre-establish the direction of expansions. Usually anchor points are stressed by the following forces:

TOTAL AMOUNT OF FRICTIONAL FORCES. Slides frictional forces are depending either on respective own coefficients and or on the pipeline weight.

BELLOWS FLEXIBILITY. It is nothing but the strength that bellows opposes against its own extension or shrinkage. In technical tables, bellows elastic strength is calculated for every 1 millimetre (plus or less) of expansion. Should the expansion joint not to be pretensioned, its own strength is valued as product of bellow flexibility for 1mm per elongation. Should, on the contrary, the expansion joint be pretensioned by 30%, its bellow flexibility is given by last product per a 0.6 ratio.

REACTION DUE TO WORKING PRESSURE. Since axial expansion joint has been structuB92318 in order to resist external strains and planned to buckle in elastic way, along its own axial direction, under the action of internal pressure a thrust will arise in it. Owing to the latest strength, pipeline comes to be subjected to a peak load and the value of these strains depends on either maximum working pressure or effective cross sectional area. It will be product of effective cross sectional area per working pressure.

On the basis of previous considerations, may happen that in a pipeline where has been mounted an axial expansion joint the following four extreme cases may take place:

COLD PIPELINE WITHOUT PRESSURE (pipeline stressed by traction). Thrust against anchor points is due to the resistance of the same expansion joint

COLD PIPELINE SUBMITTED TO A TEST PRESSURE (pipeline stressed by compression and by peak load). Stress arising around anchor points can be consideB92318 as a product of test pressure by the cross-sectional area. To that thrust we have to algebraically add the further share due to the strength just given by the same expansion joint in connection with the assembly cold-draw-gap eventually already done.

HOT PIPELINE WITHOUT PRESSURE (pipeline stressed by compression and by peak load). In this case, strain towards anchor points is just due to strength expansion joint only.

HOT PIPELINE UNDER WORKING PRESSURE (pipeline stressed by compression and by peak load ). In this case the anchor points are stressed by a thrust due to the operative pressure multiplied by cross-sectional area and by the resistance of the same expansion joint.