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Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

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512 <strong>Centrifugal</strong> <strong>Pumps</strong>: <strong>Design</strong> <strong>and</strong> <strong>Application</strong><br />

Table 19-3 Continu<strong>ed</strong><br />

Primary Alignment Measurement Methods<br />

Method Advantages Disadvantages<br />

Inside<br />

micrometer<br />

Dial<br />

indicators, in<br />

any of several<br />

arrangements,<br />

as follows:<br />

Face <strong>and</strong> Rim<br />

(see Figure<br />

19-3 A)<br />

Simple <strong>and</strong> inexpensive. No<br />

bracket requir<strong>ed</strong>. Us<strong>ed</strong> for<br />

measuring face gaps. Not<br />

limit<strong>ed</strong> to close-coupl<strong>ed</strong><br />

machines. Fairly accurate<br />

with care.<br />

Precise measurement<br />

capability with relatively<br />

inexpensive equipment.<br />

Traditional arrangement<br />

familiar to most alignment<br />

personnel. Usable with<br />

large, heavy machines<br />

having one shaft difficult to<br />

rotate for alignment<br />

measurement.<br />

Geometrically more accurate<br />

than other methods for<br />

machines with large<br />

measurement diameters <strong>and</strong><br />

short axial spans. Usually<br />

the easiest arrangement to<br />

apply to small,<br />

close-coupl<strong>ed</strong> machines.<br />

Reverse-Indicator Sleeve bearing shaft float<br />

(Rim <strong>and</strong> does not cause error or<br />

Rim). (See require special proc<strong>ed</strong>ure to<br />

Figures 19-3B avoid error,<br />

<strong>and</strong> 19-4) Geometrically more accurate<br />

Limit<strong>ed</strong> application. Does<br />

only part of the alignment<br />

job.<br />

Costs more than straight<strong>ed</strong>ge<br />

<strong>and</strong> requires more careful<br />

h<strong>and</strong>ling.<br />

If us<strong>ed</strong> with a sleeve bearing<br />

machine, shaft float can<br />

cause errors in face<br />

readings. There are at least<br />

three ways to eliminate these<br />

errors, but they make the<br />

proc<strong>ed</strong>ure more complex.<br />

Reference 6 has further<br />

details.<br />

Geometrically less accurate<br />

than reverse-indicator<br />

arrangement for situations in<br />

which axial span exce<strong>ed</strong>s<br />

face measurement diameter.<br />

This will usually be true for<br />

pumps having spacer<br />

couplings.<br />

Brackets are often face<br />

mount<strong>ed</strong>, requiring coupling<br />

spacer removal, <strong>and</strong> are<br />

more difficult to calibrate<br />

for sag. Brackets are often<br />

custom built for a particular<br />

machine rather than being<br />

"universal" variable<br />

geometry type.<br />

Inapplicable to machines<br />

having one or both shafts<br />

impractical to rotate for<br />

alignment measurement.<br />

Often impractical to use on

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