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 FOUNDATION, ALIGNMENT AND ROTATIONIf horizontal pumps are used, be sure the foundation is level, hold down bolts are tight and grouting, if used, has completely filled the baseplate (no hollows or voids) and has cured. If the pump will be handling liquid above about 150 °F (65 °C) or a steam turbine is used as the driver, an estimate of the centerline growth in height of the hot machine must be made. Shaft to shaft alignment (cold) should incorporate a deliberate, compensating off set, so that alignment is more nearly correct when equipment is up to operating temperature. Coefficients of thermal expansion for common pump case materials are:

Thermal Growth Coefficients (x10^-6)

Material inches/inch/°F mm/mm/°CCast iron 6.0 11.0

Ductile iron 6.6 12.0

Cast steel 6.5 12.1

316 Stainless steel 9.4 17.0

The coefficient is applied to the centerline height of the shafts and the difference in temperature between that at which the unit was aligned and temperature of expected operation. The cold machine should be shimmed high by the above calculated amount.

The purpose on any shaft aligning procedure is to align the centers of the machine shafts with each other, NOT to align the flexible coupling hubs. At temperature, alignment should be within 0.003 inches (0.076 mm) Total Indicator Reading (TIR), both angular and parallel. Consult a good aligning procedure to achieve or verify this degree of precision. The fact that the coupling may be rated to a much greater misalignment capability has nothing to do with the shaft-to-shaft alignment of the equipment. Survival and longevity of the machinery, NOT the coupling, are the objectives. If hot pumps and/or drivers are used, after they are at nominal operating temperature long enough for thermal growth to have stabilized (probably one hour or more), shut down the equipment and verify that alignment is within proscribed limits.

Never rely upon the alignment that was produced where the pump and drive train were assembled. Transportation, lifting and handling as well as foundation irregularities will impact alignment, always in an undesirable direction. Final alignment should be achieved as nearly the last step before actual starting of the pump. If equipment is to be dowelled in place, do so to the pump ONLY after several hours, if not days, of good operation and hot alignment checks.

The use of resilient mounts is sometimes desired to reduce vibration being transmitted into the underlying foundation. If used, such mounts must not be used beneath the pump or driver but between the pump/driver baseplate or bracket and the foundation. The pump and driver must be rigidly aligned, not resiliently aligned, as the resilient mounts will not maintain adequate alignment under torsional reactions from the transmitted torque.

Direction of rotation is critical for most equipment. It is usually indicated by arrow nameplates. Remember that some gearing will reverse rotation from input shaft to output shaft. Most engines and turbines must be purchased for a specific direction of rotation. This is also true of most pumps. Standard AC electric motors are frequently bidirectional; their direction of rotation will depend upon how the power cables are connected. It is normally not possible to predict their direction of rotation before hand. It is recommended that the flexible coupling at the motor shaft be disconnected and the motor momentarily energized (jogged on, then immediately off) to see if its rotation is correct for the rest of the driven equipment. If not, two of the electric power cables will need to have their connections reversed. Verify correct rotation after reversing, if necessary, before re-engaging the flexible coupling.

Check back in a few days for additional content on rotary pump startups.

For more information, contact Jim Brennan at

This entry was posted on Monday, January 19th, 2009 at 1:54 pm and is filed under Jim Brennan Blog. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.