The Fundamentals Of Centrifugal Pump Alignment And Shimming

Centrifugal pumps are common throughout Australian processing plants, water utilities, mining operations, food facilities and energy sites. They transfer everything from clean water and cooling fluids to hydrocarbons, slurry and chemically aggressive liquids. Their reliability depends on several connected factors, yet shaft alignment and correct shimming are among the most important and most frequently misunderstood.

A pump and its driver can appear to run smoothly while suffering from angular or parallel misalignment. The resulting forces travel through the coupling, bearings, seals, baseplate and connected pipework. Learning how to inspect, measure and correct these conditions gives maintenance teams a practical way to reduce vibration, extend component life and improve plant availability.

Why Shaft Alignment Matters

A typical pump set consists of a pump, motor, coupling, baseplate and associated pipework. The motor drives the pump shaft through the coupling, but the shafts must share a controlled centreline. If the centreline changes between the coupling ends, the set is misaligned.

Parallel misalignment occurs when the two shaft centre lines are offset but remain parallel. Angular misalignment occurs when the centre lines meet at an angle. Real installations often have a combination of both. The coupling may tolerate a small amount of movement, but it should not be treated as a permanent correction for poor installation.

Misalignment increases radial and axial loads on rolling-element or sleeve bearings. It can also cause coupling element wear, elevated vibration, seal leakage, high motor current and premature shaft fatigue. In a remote mining operation in Western Australia or a large processing facility near Gladstone, an avoidable pump failure can involve substantial production losses, specialist travel and long replacement lead times.

Correct alignment is especially important for pumps operating continuously, at high speed or with high-pressure service. However, even a small utility pump can experience repeated failures if its baseplate is distorted, its pipework is pulling on the casing or its feet are supported by an inconsistent stack of shims.

Preparing The Pump Set

Alignment work begins with a safe and stable installation. The equipment must be isolated, locked out and tagged in accordance with the site’s electrical and process safety procedures. Stored pressure, hot liquid, rotating energy and automatic starting systems must be controlled before guards or coupling components are removed. Australian sites commonly apply formal permit-to-work, isolation and verification systems under their workplace health and safety arrangements.

Clean the mounting feet, baseplate, soleplates and hold-down bolts before taking measurements. Remove rust, paint flakes, burrs and dirt from contact surfaces. Check that the baseplate is properly supported and that its anchor bolts are secure. A soft foot condition exists when one or more equipment feet do not sit firmly on the baseplate. Tightening the hold-down bolt then distorts the pump or motor frame.

Soft foot should be checked before final alignment. One practical method is to loosen one foot bolt at a time while observing movement with a dial indicator or laser system. If the foot moves significantly, measure the gap and correct it with suitable shims. Do not use excessive bolt torque to force a distorted foot into position.

The pipework must also be free from strain. Disconnecting a flange or carefully checking the coupling movement can reveal whether the suction or discharge piping is pulling the pump casing away from its natural position. Pipe strain may change when bolts are loosened, and the equipment may move again when the line is reconnected. The correct remedy is to support, reroute or modify the pipework rather than compensate by shifting the pump.

Measuring Shaft Position

Before measuring, check the coupling manufacturer’s instructions and the pump supplier’s alignment limits. Required tolerances depend on shaft speed, coupling type, bearing arrangement, operating temperature and service duty. A high-speed process pump in an oil and gas facility will generally need tighter control than a slow-speed utility pump.

Straightedge and feeler-gauge methods can provide a rough check, but they are limited by coupling geometry and operator judgement. Rim-and-face dial indicator methods are more precise when used correctly. Laser alignment instruments can measure both angular and offset conditions efficiently, while also accounting for measurement positions and shaft rotation. The instrument is valuable, but it does not replace clean surfaces, good brackets and sound mechanical judgement.

Take readings by rotating the shafts together where possible, commonly through 90-degree positions. Record the vertical and horizontal values, then distinguish between movement required at the front and rear feet. A common mistake is to move the motor without understanding whether the reading represents an offset, an angle or a combination of both.

Alignment should be checked in both vertical and horizontal planes. The vertical correction normally involves shimming or removing material beneath the motor feet. The horizontal correction involves controlled side-to-side movement, often using jacking bolts. Avoid striking the motor with a hammer, as this can damage the frame, bearings or coupling and makes the adjustment difficult to repeat.

The final target is not automatically zero at every reading. Pumps may require a cold alignment offset to account for thermal growth. When a motor, pump or casing operates at a different temperature, each component expands according to its material, length and temperature change. The manufacturer’s thermal growth data should determine the target. If no reliable data is available, the engineering team should establish a documented basis rather than guessing.

Correcting With Shims

Shims establish the vertical position of the movable machine, usually the motor. They should be clean, flat and sized to provide solid support under the entire foot. Stainless steel shims are widely preferred because they resist corrosion and maintain their thickness better than improvised materials. Soft packing, folded sheet metal, washers, excessive quantities of thin shims and materials that can creep should not be used as permanent alignment supports.

Use as few shims as practical while retaining full foot contact. A controlled shim pack may contain a thicker base shim with thinner adjustment shims above it. Keep the pack organised and record its thickness at each foot. Tapered, damaged or contaminated shims can introduce a new soft foot condition after the original misalignment has been corrected.

To raise a motor foot, add the measured shim thickness. To lower it, remove shims or machine the mounting surface where this is an approved engineering solution. Make small corrections, tighten the hold-down bolts to the specified sequence and torque, then remeasure. Every tightening cycle can alter the result, so alignment is complete only after the bolts are secure and the readings remain within the selected tolerance.

Horizontal movement should be made with jacking bolts where fitted. Loosen the appropriate hold-down bolts enough to allow movement, protect the threads and make gradual adjustments. Recheck the coupling gap and any axial position requirement after each correction. A motor that is aligned at the coupling but incorrectly positioned along the shaft may still overload the coupling or create unwanted thrust.

When the readings are acceptable, inspect the coupling for correct gap, element condition, key fit and guard clearance. Install the guard before operation. A final check should confirm that pipework is connected without pulling the pump, the baseplate is secure and lubrication systems are ready.

Verification And Ongoing Reliability

Alignment should be verified after the pump has been run under normal conditions where practicable. Operating temperature can produce movement that was not visible during a cold alignment. Record cold readings, target offsets, shim thicknesses, bolt torque and final results in the maintenance system. This history makes future work faster and helps identify recurring foundation, pipe strain or thermal growth problems.

Use vibration monitoring to support the alignment decision. Increased vibration at running speed, coupling-related frequencies or axial directions can indicate misalignment, although similar symptoms may arise from imbalance, looseness, resonance, cavitation or bearing damage. Temperature checks, oil or grease condition, seal performance and motor current provide additional evidence.

Cavitation deserves particular attention on Australian sites that pump from tanks, dams or long water lines. A pump can be correctly aligned and still suffer damage if suction conditions are poor, strainers are blocked or the liquid temperature reduces available net positive suction head. Alignment work should therefore sit within a wider commissioning and reliability process rather than being treated as an isolated task.

The following comparison gives a practical guide to common alignment approaches. The acceptable result must always come from the equipment manufacturer, site engineering standard or recognised maintenance procedure.

Alignment approach	Useful for	Main strengths	Important limitations
Straightedge and feeler gauge	Preliminary checks and low-speed equipment	Fast, inexpensive and simple	Low precision; affected by coupling condition and operator judgement
Rim-and-face dial indicators	Skilled maintenance teams and many standard pump sets	Accurate when brackets and readings are correctly managed	Requires careful setup, shaft rotation and calculation
Laser alignment system	Routine industrial alignment and complex machine trains	Quick measurements, clear correction values and good repeatability	Requires calibration, correct setup and trained users
Cold alignment with thermal target	Hot pumps, high-speed drivers and process service	Compensates for expected operating growth	Depends on trustworthy temperature and growth data
Final alignment with pipework connected	Commissioning and post-maintenance verification	Reveals movement caused by piping or support conditions	Unsafe if isolation is incomplete and difficult if access is restricted

A well-controlled alignment job should leave the pump set with stable feet, appropriate shims, secure fasteners, acceptable coupling readings and no external pipe strain. Training in a realistic live-process-plant environment can help apprentices and experienced tradespeople connect these measurements with the operating behaviour of real equipment. For employers in Melbourne, Brisbane, Perth, Newcastle and the wider Australian market, practical capability is valuable because alignment quality directly affects safety, maintenance cost and production continuity.

HCF CATCH provides hands-on industrial training across process, engineering, energy, electrical and safety disciplines, with facilities designed to reflect working plant conditions. Employers can use practical training to build consistent alignment methods, while individuals can strengthen the mechanical skills required for pumps, rotating equipment and broader reliability work. Explore the relevant training options, apprenticeship pathways and facility capabilities through HCF CATCH.