Page 122 - Machinery Component Maintenance

Muchinerx Foundurions und Grouting 105

The question has been asked, “Why should a $75-$1 10/ft3 epoxy grout
be used in place of a $30/ft3 cementitious grout‘?” There are two reasons
to pay the additional “one time cost.” Epoxy grout applied to a properly
prepared baseplate bonds with a tensile strength of 2,000 psi. This trans-
forms the baseplate into a monolith with the concrete foundation. Forma-
tion of a single block lowers the natural frequency of the pump baseplate,
which reduces pump shaft vibration caused by resonance. Observation of
pumps that had been installed with the new grouting procedure revealed
longer “mean time between failure” (MTBF) over existing pumps. Older
pumps had vibration levels from 0.3 to 0.5 in./sec (IPS) as compared to
less than 0.15 IPS for the new pumps.
The second reason to use epoxy grout is that it seals the concrete foun-
dation to prevent damage from moisture and oil seepage. Since there is
no bond when cementitious grout is used, it is likely that moisture or oil
will get between the underside of the baseplate and foundation.

Baseplate Leveling Procedures
It is necessary to discuss the baseplate leveling procedure first in order
to fully understand certain baseplate and foundation preparations. These
preparations must be performed before placement of the baseplate on the
foundation.
The following assumptions are made concerning the pump foundation:
The foundation should rest on solid or stabilized earth, completely
independent of other foundations, pads, walls, or operating plat-
forms. A minimum of 3,000-psi steel-reinforced concrete should be
used.
The foundation should be adequately designed to support the pump.
Foundation mass for centrifugal pumps should be at least three times
the mass of the pump, driver, and baseplate. The reciprocating pump
foundation mass should be at least five times the pump system mass.
The foundation should be designed to avoid resonant vibration condi-
tions originating from normal excitation forces at operating speed or
multiples of the rotating speed.
The pump, gearbox (if used), and driver should rest on a common
foundation.
0 The foundation should be designed for uniform temperatures to re-
ducc distortion and misalignment (boiler feedwater pump applica-
tions).
Do not take these assumptions for granted. Check the foundation at the
design stage, not after it has been poured. There are some good computer
programs available for foundation designs.
There are four popular methods used to support the pump baseplate
while the grout is poured and cured. Figure 3-21 illustrates the four