PUMP ALIGNMENT

Power is transmitted from a motor to a pump by connecting the motor and pump shafts. They can be directly connected using a straight shaft or joined together by a flexible coupling. In some systems, belts are also used between the motor and the pump or the motor and the coupling.
Misaligned shafts lead to costly and unplanned downtime. They also often result in damaged seals. Consequently, broken seals can cause lubrication problems and leaks.

Misalignment can occur in three ways:

Radial (offset or parallel) misalignment :
The centerlines of the two shafts are parallel but offset.
Axial (or end float) misalignment :
The two shafts are aligned but one (or both) axles are prone to in/out movement along the centerline
Angular misalignment :
The centerlines of the two shafts are not parallel.

Shaft misalignment occurs when the shaft or surface is dislocated from its ideal position. Misalignment is the deviation in the shaft position when the pump is operating at standard conditions. Misalignment can lead to troubles in either a section of the pump or its entirety. Misalignment is a problem even for pumps with flexible couplings. Though a flexible coupling has more room for movement than a standard coupling, it can only function with small misalignment.

Types of shaft Alignment methods:

To maintain good alignment, it is important to minimize vibrations by securing the pumping system to sound foundations. Industrial pumps are normally bolted directly to a machined baseplate and other equipment is aligned and secured to it. The entire assembly is sited on a concrete foundation and affixed with epoxy or cement grouting. When constructed properly, overall vibrations can be substantially reduced because of the damping effect of the foundation mass. As a general rule, foundations should be at least three times the mass of the pumping system for centrifugal pumps and five times for reciprocating pumps.

Misalignment in pumps can lead to several troubles like:

Hence, one must detect the signs of misalignment as soon as it occurs to prevent the catastrophic failure of the pump.

Shaft and belt misalignment can be a result of several factors such as:

Soft foot is a condition in which one of the feet of a pump does not sit flat on the baseplate. Soft foot is among the most common causes of misalignment. To check, operators should first assess the equipment’s foundation and employ a suitable shaft alignment tool to identify and correct potential soft foot conditions. Some laser-guided alignment tools have a soft foot operation capability that guides the operators through corrective procedures.
Bearings out of square with their housings are another common cause of misalignment. Often a condition of wear, the out-of-square bearing and/or its housing will need to be corrected or replaced to bring pumps back into alignment.

Other possible causes include:

During operation at temperature, expansion of the drive shaft and other pump components can affect a pump’s alignment. This effect is called thermal growth and must be taken into account when selecting and fitting a shaft coupling and when correcting shaft alignment.

Noise and vibrations can be the first indications of problems with a running pumping system. Vibrational analysis, performed as part of a preventative maintenance and monitoring programmed, can identify if shaft misalignment is becoming a problem. The diagnosis for shaft misalignment is indicated by abnormally high vibration levels at one and/or two times the shaft rotational rate frequency. Rapid identification of misalignment in this way can save a pumping system from damage.

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