Q: Is there a simple way to check the alignment of flexible couplings on a pump?
A: Laser alignment systems are used to determine the extent of shaft misalignment by measuring the movement of a laser beam across the surface of a detector plate as the shafts are rotated.
Many laser alignment systems are available, and the procedure for alignment is provided by the laser system’s producer. They are capable of aligning couplings with and without spacers and are most commonly used for precision alignments. Image 1 shows an example of a laser alignment system setup on a pump and motor shaft. By following the instructions of the laser system, the computer will output adjustment requirements to align the shafts.
In the absence of a laser alignment system, users can check the alignment with some simple tools. The necessary tools used for checking the alignment of a flexible coupling are a straightedge and a taper gauge or a set of feeler gauges, or by use of dial indicators.
A rough check for angular alignment is made by inserting the taper gauge or feelers between the coupling faces at 90 degree intervals (see Image 2). Checks for angular and parallel alignment by this method can only be done if the face and outside diameters of the coupling halves are square and concentric with the coupling bores. A rough check for parallel alignment is made by placing a straightedge across both coupling rims at the top, bottom and at both sides (see Image 3). After rough alignment, fasten the indicator to the pump half of the coupling, with the indicator button resting on the other half coupling periphery (see Image 4). Set the dial to zero, and mark the coupling half beside where the button rests. Rotate both shafts by the same amount, i.e., all readings on the dial must be made with the button beside the mark. The dial readings will indicate whether the driver has to be raised, lowered or moved to either side.
After each adjustment, recheck both parallel and angular alignments. Accurate alignment of shaft centers can be obtained with the dial indicator method — even where faces or outside diameters of the coupling halves are not square or concentric with the bores—provided all measurements for angular alignment are made between the same two points on the outside diameters. For angular alignment, change the indicator so it bears against the face of the same coupling half and proceed as described for parallel alignment.
There are additional techniques not described in this answer that are required for proper pump alignment, such as correcting for indicator sag or compensating for cold aligning a hot pump system. Please reference industry standards and the pump and coupling manufacturer’s instructions as well.
For more information about coupling alignment for rotodynamic pumps, including additional considerations, see the American National Standard ANSI/HI 14.4 Rotodynamic Pumps for Manuals Describing Installation, Operation, and Maintenance at pumps.org.
Q: What is meant by the temperature class for my pumps that are rated for explosive atmospheres?
A: Pumps installed in potentially explosive atmospheres must be designed and operated in a way to limit their surface temperature based on the type of potentially explosive atmosphere.
A reference for the requirements of electrical and nonelectrical equipment is the European Union (EU) ATEX Directive 2014/34/EU (Ex). Within this directive, one requirement is that pumps have a temperature class as stated in the explosion (Ex) rating on the nameplate. These are based on a maximum ambient temperature of 40 C (104 F). Refer to the manufacturer for higher ambient temperatures.
The surface temperature on the pump is influenced by the liquid handled. The maximum permissible liquid temperature depends on the temperature class and must not exceed the values in Image 5. The temperature rise at the seals and bearings due to the minimum permitted fl ow rate is taken into account in the temperatures stated. Note that the plant operator is responsible for compliance with the specified maximum liquid temperature. Surface temperatures above 54 C (130 F) can cause irreversible skin damage and, therefore, require insulation to ensure personnel protection. For more information about the manuals describing the installation, operation and maintenance of rotodynamic pumps, refer to ANSI/HI 14.4 Rotodynamic Pumps for Manuals Describing Installation, Operation, and Maintenance at pumps.org.
HI Pump FAQs® is produced by the Hydraulic Institute as a service to pump users, contractors, distributors, reps and OEMs. For more information, visit pumps.org.
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