Generally, a flex-coupled pump will be aligned (that is, the motor and pump shafts will be aligned) prior to shipment, either at the factory or at the shop of the pump distributor. This often leads owners and installing contractors to think that they do not need to check alignment during the installation phase. This is a myth.
When a pump is shipped on a truck to the construction site, it undergoes a great deal of shock and vibration. One study I read yesterday measured peak G-forces at 10G’s. Said another way, a pump weighing 800# undergoes forces of 8,000#, probably several times during the shipment and lesser forces constantly, as the truck starts, stops, turns and hits bumps in the road. In addition, a good deal of vibration exists in transit.
Consider that it really is friction that holds the pump and motor in place. Yes, there are hold down bolts, but the bolts really serve as devices to increase the force between the pump base and the pump/motor feet.
The combination of forces and vibration overcome friction and often cause the pump and motor to shift a bit during shipment. The amount of “shift” will often not be enough to be noticeable to the naked eye but will be enough to exceed the misalignment limits of the coupling.
The results are reduced coupling life and very often, there will be a noticeable vibration when the pump is operated. More severe misalignment may eventually result in early bearing failure.
Therefore, it is always best if flexibly-coupled pumps be aligned as part of the installation procedure. For a consulting engineer, this means a spec item that calls for field alignment as part of the commissioning process. For a contractor, this means to provide an alignment as an element of quality control, even if the spec does not call for it. For the owner, it means asking for field alignment and an associated report for any flex-coupled pump purchased. The alignment may be performed by the contractor or the pump supplier.
In the HVAC industry, it was once common and still is in some situations, with certain coupling types, a matter of a straight-edge alignment to meet the pump and coupler manufacturer’ requirements. The trend, however, is for increased use of optical/laser alignments, which are generally more accurate, at least in the hands of experienced technicians.
So, it’s not that one should not trust the factory or distributor alignment. It’s simply a fact that things will often shift during transit. To guard against early coupling and even bearing failure, a field alignment really IS important.