Do not weld near any rubber expansion joint or weld the mating flanges with the expansion joint in place. There is the possibility of fire, spark or heat damage.


All pipe lines should be properly supported so that the expansion joints do not carry the pipe load.


a. Anchors are to be provided upstream and downstream of the expansion joints at both ends of the thermally expanding or contracting pipe length. Expansion joints will not function and may very well over extend and fail unless these full thrust anchors are in place.

b. Where a shut-off valve, reducing valve, check valve or any mechanical pipe fitting is installed in the expansion joint line, check with the manufacturer to be certain the pipe fitting can take the expansion joint thrust. If not, the pipe must be anchored on either side of the fitting and install two expansion joints rather than one. The thrust on the anchor is the pipe line area plus the arch area multiplied by the water pressure. The pipe wall thrust is only the area of the arch multiplied by the water pressure.


If it is not possible to anchor the pipe line in the above manner, control units must be used. Once a control unit is installed, if there is no anchor on one or both sides of the expansion joint, the expansion joint will open up to the control rod lock out position and remain in that position. The expansion joint will not act to take up axial motion. It will make up for misalignment, transverse and possibly angular motion.

Where transverse forces are to be kept to a minimum, chain or cable assemblies should be substituted for the rigid control rods. While spherical seats on the control rods are of some value, the force required to move piping laterally when control rods are used, remains very high.


All pipes are to be lined up accurately before installing expansion joints. Although rubber units will adjust themselves to misaligned flanges within the specified limits, it is difficult to force expansion joints into position before they are rigidly bolted to the flanges. Initial misalignment should be kept to a maximum of 1/8”.


a. Expansion joint flanges must be in contact with a continuous surface. Depressions or protrusions typical of victaulic or similar flanges must be covered with a steel cover flange first.

b. Rubber flanges will not retain loose elements in valve bodies that rely on contact with a steel flange. A steel cover flange must be inserted between the rubber expansion joint and the valve body.

c. Apply a thin film of graphite dispersed in glycerin or water to the face of the rubber flanges before installing. No other type of lubricant or seal should be used on the flange face. The graphite prevents the rubber from adhering to the metal flange so that the rubber pipe or joint can be removed without damage, should it ever be necessary.


While it is occasionally cost effective to install expansion joints in pre-compressed or elongated positions to increase travel in the opposite direction, it is best to install them in normal lengths, avoiding compression or elongation.


Continued support of expansion joint is required until the expansion joint is fully bolted into place.


It is preferable to install bolts with SAE washers. While it is not always possible because of arch interference, it is also preferable to install the bolts with the head next to the rubber arch. This eliminates the possibility of using over long bolts with the bolt protruding past the nuts and cutting into the rubber arch. When bolts must be installed from the pipe line side, limit bolt length to 1/8” of thread protruding from the nut.


Use two wrenches when tightening bolts. Unlike steel flanges where you normally tighten opposite bolts, when tightening the back up rings of rubber flanges, tighten bolts sequentially until the rubber flange bulges uniformly between the back up ring and the adjoining pipe flange. This tightening process continues until bolts are fully torqued.

Rubber flanges relax. Bolt tightness should be checked several days after initial operation, and periodically thereafter to prevent leakage. This is particularly important in pipe lines where the service changes from hot to cold and vice versa during heating and cooling cycles.


Any gouges or cracks in the cover that develop after installation, should be sealed, even though they do not appear to be serious. This can be done by coating with rubber cement, thus preventing oil or water from penetrating the fabric carcass. The Mercer Rubber Company sells special cements for this purpose. Should you wish to order, please specify the material that the joint cover is made of, such as Natural Rubber, Neoprene, Hypalon, etc.


Never operate expansion joints above rated pressures or temperatures.


Do not lift the expansion joints by the bolt holes. They may be lifted by a padded sling or the two ends of a piece of pipe passing through the joint. Another convenient method is to cut the lifting pipe longer than the joint, and lift it by means of a chain or cable running through the pipe. It is preferable not to roll joints on their flanges. Transport them to the position of installation and install them without contact with the floor wherever possible.