Parallel misalignment is the offset of two mating shaft centerlines although the centerlines remain parallel to each other. Angular misalignment is two shaft centerlines intersecting at some angle other than zero degrees. End float is the relative displacement of one shaft end with respect to the other.

A single-flex coupling accepts angular misalignment only. That means it acts as a hinge or a pivot and cannot accept parallel misalignment. A double-flex coupling accept both angular and parallel misalignment. It may be visualized as two single-flex couplings with a short spacer or distance between the pivots. Depending on their design, both single-flex types may or may not accept end float. A rigid coupling, as its name implies, is merely a set of rigid flanges mounted on a shaft. It cannot compensate for or permit any misalignment.

• Floating Shaft – applicable to both shaft and flange type torquemeters. Use a single flex coupling at each shaft end to accommodate angular misalignment
• Floating Mounted – for shaft style torquemeters only. Use a double flex coupling at each shaft end to handle both parallel and angular misalignments.alignments.

BEST INSTALLATIONS

INCORRECT INSTALLATIONS

THE TORQUEMETER IN THE ABOVE INSTALLATION NOT CONSTRAINEDIN THE RASIAL DIRECTION.
THIS LACK OF CONSTRAINT WILL ALLOW THE SHAFT SYSTEM TO ROTATE ECCENTRICALLY.WITH RESULTING HIGH VIBRATIONS AND MOST LIKELY CATASTROPHIC FAILURE.

RIGID COUPLINGS AS USED ABOVE FORCE THE SHAFTS INTO ALIGNMENT BY BENDING YHEM. THE DEGREE OF BENDING IS UNKNOWN, BUT COULD BE CONSIDERABLE IF MISALIGNMENT IS HIGH OR IF ALL COMPONENTS ARE EXTREMELY RIGIDAND WILL CHANGE WITH TEMPERATURE GROWTH. THIS BENDING LOAD WILL CAUSE EXCESSIVE WEAR AND PREMATURE FAILURE.

THE SUBSTITUTION OF ONE SINGLE-FLEX COUPLING AS SHOWN ABOVE IN PLACE OF A RIGID COUPLING IN THE PREVIOUS EXAMPLE DOES NOT IMPROVE THE INSTALLATION. THE SHAFTS
ARE STILL FORCED INTO ALIGNMENT BY BENDING THEM.

SINGLE-FLEX COUPLINGS IN THE ABOVE INSTALLATION WILL NOT ACCEPT THE PARALLEL SHAFT MISALIGNMENT THAT WILL EXIST. FORCING THE INSTALLATION WILL RESULT IN BENDING MOMENTS ON THE SHAFT AND PREMATURE SYSTEM FAILURE.