SP | Flexible Couplings | Misalignment | Alignment
FLEXIBLE COUPLINGS
A flexible coupling should not be used to compen-
sate for misalignment of the pump and driver
shafts. The purpose of the flexible coupling is to
compensate for temperature changes and to
permit end movement of the shafts without
interference with each other while transmitting
power from the driver to the pump.
TYPES OF MISALIGNMENT
There are two forms of misalignment between the
pump shaft and the driver shaft, as follows:
1. Angular misalignment-shafts with axes
concentric but not parallel.
2. Parallel misalignment-shafts with axes parallel
but not concentric.
Angular misalignment
A check for angular alignment is made by inserting
the taper gauge or feelers at four points between
the coupling faces and comparing the distance
between the faces of four points spaced at 90-de-
gree intervals around the coupling. The unit will be
in angular alignment when the measurements
show that the coupling faces are the same distance
apart at all points.
Parallel misalignment
A check for parallel alignment is made by placing a
straight edge across both coupling rims at the top,
bottom and at both sides. The unit will be in paral-
lel alignment when the straight edge rests evenly
on the coupling rim at all positions. Allowance may
be necessary for temperature changes and for
coupling halves that are not of the same outside
diameter. Care must be taken to have the straight
edge parallel to the axis of the shafts. Angular and
parallel misalignment is corrected by means of
shims under the motor mounting feet. After each
change, it is necessary to recheck the alignment of
the coupling halves. Adjustment in one direction
may disturb adjustments already made in another
direction. It should not be necessary to adjust the
shims under the pump.
COUPLING ALIGNMENT
The faces of the coupling halves should be spaced
far enough apart so that they cannot strike each
other when the driver rotor is moved hard over
toward the pump. Due allowance should be made
for wear of the thrust bearings. A minimum dimen-
sion for the separation of the coupling halves is
specified by the manufacturer, usually 3.2mm, the
necessary tools for approximately checking the
alignment of a flexible coupling are a straight edge
and a taper gauge or a set of feeler gauges.
GROUTING
When the alignment is correct, the foundation
bolts should be tightened evenly but not too firmly.
The unit can then be grouted to the foundation.
The base plate should be completely filled with
grout and it is desirable to grout the levelling
pieces, shims or wedges in place. Foundation bolts
should not be fully tightened until the grout is
hardened, usually about 48 hours after pouring.
FINAL CHECK OF ALIGNMENT
After the grout has set and the foundation bolts
have been properly tightened, the unit should be
checked for parallel and angular alignment and, if
necessary, corrective measures taken. After the
piping of the unit has been connected, the align-
ment should be again checked.
V-BELT ALIGNMENT
Although alignment is not as critical in V-belt
drives as in others, proper alignment is essential
for long belt and sheave life. First, make sure that
drive shafts are parallel. The most common causes
of misalignment are nonparallel shafts and
improperly located sheaves. Where shafts are not
parallel, belts on one side are drawn tighter and
pull more than their share of the load. As a result,
these belts wear out faster, requiring the entire set
to be replaced before it has given maximum
service. If misalignment is in the sheave, belts will
enter and leave the grooves at an angle, causing
excessive belt cover and sheave wear.
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