Proper Pump to Motor Alignment Techniques: Part 2 of 6
Depending upon the alignment method chosen (reverse indicator, rim and face, double rim, etc.), specific alignment parameters must be established, measured and subsequently corrected in order to achieve the desired final machine alignment. In this guide, we will discuss the modern laser alignment method, and the associated parameters in terms of angularity and offset. Each of these parameters are measured in horizontal (plan view) and vertical (side view) planes, yielding a total of four measurements: Vertical Angularity, Horizontal Angularity, Vertical Offset and Horizontal Offset.
Angularity describes the angle between the two rotating axes. There are multiple means of expressing the magnitude of angularity. Some systems utilize units of degrees while others refer to angularity in units of slope in mils/inch for example. Ultimately the angularity is translated into a “Gap” measurement, which is essentially the angularity extrapolated out to the coupling diameter.
Offset describes the distance between the rotational axes at a specified point in space. Offset is commonly incorrectly referred to as “rim misalignment”. In most cases, the shaft rotational axes are not perfectly parallel, meaning that that coupling rim has an unknown relationship to the shaft rotational axes. Offset values are typically measured in “mils” or thousandths of an inch.
As the figure above depicts, for the same alignment condition, the offset value varies widely depending upon the location that the measurement is taken. For this reason, the industry standard location for offset measurements is understood to be at the center of the coupling interface. The figure below summarizes both angularity and offset alignment conditions.
Continue reading in our next post for more information about ‘Proper Pump to Motor Alignment Techniques’. Part 3 focuses on ‘Alignment Precision’.