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

506 Centrifugal Pumps: Design and Application
vironmental factors. More specifically, epoxy is more expensive and less
resistant to high temperatures, but has higher early and ultimate strength
and greater chemical and impact resistance than inorganics. It is also easier
to place properly and to cure.
With either category of grout material, success depends on careful
planning and preparation and attention to numerous details such as site
preparation, equipment selection, and a stepwise procedure for proportioning
and mixing, placement, curing, and protective coating. (For more
thorough coverage of this subject, see Bloch [1] and Murray [12].)
Piping Fit and Support. Here, the object is to avoid excessive pump
nozzle loading. Piping fit is a function of installation workmanship and
effective construction inspection/quality control. Piping flexibility and
support are functions of design, with due consideration given to weights,
stiffnesses, and thermal effects. If not carefully designed to avoid such
problems, heavy, hot piping can become "the tail that wags the dog,"
with the dog being the pump.
Flexible Coupling. Choice of flexible coupling can be important. Tradition
and price are the two most often used criteria, and either can result in
a poor choice. For most pumps, it is desirable to use a spacer coupling.
This gives more parallel misalignment capability than a close coupling of
the same type and also provides better access for maintenance.
If radial space is limited, a gear coupling may be required. This will
transmit more horsepower at a given speed than any other type occupying
the same space. It is, however, more sensitive to misalignment than other
types and also requires lubrication. The latter factor is no longer as much
of a disadvantage as it once was though, because non-separating coupling
greases are now available. A gear coupling can handle limited end float
applications for sleeve bearing motors, but doing this correctly can get
complicated.
Gridmember couplings are another relatively inexpensive lubricated
design used mostly for the smaller pumps.
Elastomeric couplings are popular for pumps in certain size and speed
ranges. These accommodate fairly large misalignments, but are sensitive
to high temperatures (including heat caused by rubbing against a coupling
guard) and certain chemicals. This type of coupling may be unable
to handle sleeve bearing motor limited end float applications well.
Dry metallic flexing element couplings are available in several designs—disk,
diaphragm, and cantilever link. Chloride stress corrosion
cracking is sometimes a problem, but can be minimized by judicious
choice of element material, for example, type 316 stainless steel in preference
to type 304. These couplings are a good choice for use with sleeve