The alignment of coupling is one of the important tasks of pump installation. The aim of alignment is to make the center line of motor shaft and pump shaft in the same straight line when the pump is working. The accuracy of alignment is related to the normal operation of the machine, especially for high-speed pumps.

Absolute and accurate alignment of two axes is difficult to achieve. It is even more difficult to keep accurate alignment of continuous running machines. The uneven thermal expansion of parts, the deflection of axles, the uneven wear of bearings, the displacement of pumps and the uneven subsidence of foundations all result in the uneven alignment of axles to Germany. The reason is that there is an allowable deviation in the center of two axes when designing the pump, which is also needed when installing the coupling. From the assembly point of view, as long as the coupling can transmit the torque safely and reliably, the bigger the allowable deviation in the center of two axes, the easier it is to meet the requirements when installing. However, from the point of view of installation quality, the smaller the deviation between the centerline of the two axes, the more accurate the alignment, the better the operation of the machine and the longer the service life. Therefore, the allowable deviation of the two axes alignment when the coupling is installed can not be regarded as the allowance left by the erector's hasty construction.

1. Analysis of the two-axis offset when the coupling is aligned. When the pump is installed, the coupling will deviate or tilt in the axial and radial directions.

2. Measurement methods

When installing the machine, the coupling is usually aligned after the central position of the pump is fixed and the level is adjusted. By measuring and calculating, the deviation is analyzed, and the center position of motor shaft is adjusted so that the motor shaft and pump shaft are both concentric and parallel.

There are many ways to align the coupling. The commonly used methods are as follows:

1. Simple measurement method, using angle ruler and plug ruler to measure the radial deviation in all directions of the outer circle of the coupling, and using plug ruler to measure the axial clearance deviation between the end faces of the two-half coupling, through analysis and adjustment, to achieve the alignment of the two axes. This method is simple to operate, but has low accuracy and large alignment error. It is only suitable for the installation and measurement of coupling with low speed and low alignment requirement.

2. There are many kinds of structure forms of center card (also known as pair wheel card) which can be corrected by measuring method of center card and plug ruler. According to the structure of coupling, the suitable center card is selected according to its size. There is no uniform specification for the center card. The fitter will make it by himself, considering the requirements of measurement and assembly.

(a) Adjustable double-point wheel-to-wheel clamp fixed on coupling with steel strip;

(b) Non-adjustable double-point wheel-to-wheel card for measuring axle;

(c) Adjustable double-point pair wheel clamp for measuring gear coupling;

(d) Adjustable double-point wheel-to-wheel clamp fixed directly on the coupling with screw;

(e) Adjustable single-point-to-wheel clips with smooth cylindrical surface couplings;

(f) Adjustable two-point pair-wheel clamp for smooth cylindrical surface couplings; the radial and axial clearances of the couplings can be measured simultaneously by using central clamp and plug ruler. This method is simple to operate and has high measurement accuracy. The adjustment can be calculated by using the measured clearance value, so it is more applicable.

3. Percentimeter measurement method installs special fixture (pair wheel clip) or magnetometer seat on the half-coupling used as reference (usually mounted on the pump shaft). Percentimeter is used to measure the deviation of the radial and axial clearance of the coupling. This method greatly improves the measurement accuracy of coupling alignment.

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