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Pumps & Systems, March 2008

Q.  

When installing a horizontal pump, is it better to grout the pump baseplate or let it float free?   Different sources provide opposing views on this subject.

A.

Whether to grout depends on the specific application and the design of the baseplate. Applications that undergo wide temperature variation may do well with floating baseplates to allow for movement of the pump and to minimize pipe strain caused by thermal expansion of the pipe. However, the baseplate in such cases must be stiff enough to avoid misalignment of the shaft coupling as the baseplate moves.

The grouted baseplate is designed to allow grout to be poured underneath and inside the base. The grout placed inside the base contributes to the baseplate's installed rigidity and damping. The cross members in this type of base are normally designed to lock into the grout and further resist deflection or vibration of the baseplate. Typically, the cross member geometry chosen to achieve this is an L-section, T-section or I-section.

If the baseplate is closed on top, then grout holes must be provided to allow the grout to be placed inside the base.

Figure 1.3.8.2.1a shows a typical grouted baseplate design.

A freestanding baseplate is intended to be elevated off the floor and supported by stilts, shims or springs. See Figure 1.3.8.2.5a. This type of baseplate must be designed to provide its own rigidity, as there is no grout for additional support.

The features of this type of baseplate are:

• The need for concrete foundation pads is eliminated
• An allowance for height adjustment can easily be included
• Spring-mounted bases provide vertical displacement under applied loads associated with thermal expansion of the piping
• Optional addition of slide bearing plates may also be provided below the stilts or springs to allow horizontal displacement associated with thermal expansion of the piping

More detail on baseplates can be found in the recently revised HI Standard ANSI/HI 1.3-2007 Rotodynamic (Centrifugal) Pumps for Design and Application.