How to Pick an HVAC Centrifugal Pump Part 2: Types of Pumps and Seismic Considerations

By Chad Edmondson (JMP) and Norman Hall (RLD)

One of the first decisions one must make when selecting a pump is whether to use a base-mounted or an inline pump. 

Based mounted pumps, as the name suggests, have all their components (pump, motor, and bearing assembly) all mounted on a common base. They arrive at the jobsite ready to be installed on a concrete foundation.  With end-suction base mount pumps, water enters the suction end horizontally and exits vertically out the top of the volute.  They may be close coupled style with no coupler (ESCC) or floor mounted long coupled style which has a coupler (ESFM . The coupler joins the motor shaft to the pump shaft.  Large double suction base-mounted pumps can be provided with various suction and discharge configurations.

Floor mounted long coupled base-mound pump.

Floor mounted long coupled base-mound pump.

Close coupled base-mounted pump

Close coupled base-mounted pump

Inline pumps are traditionally mounted in the piping line and the weight of the pump is supported by the pipe and/or pipe hangers. They may be horizontal style with the motor mounted horizontally or vertical style with the motor mounted vertically above the pump. Smaller pumps, sometimes called “booster pumps,” are traditionally less than 2 HP and tend to be horizontally mounted. The larger inline pumps tend to require more support and are more commonly referred to as inline (ES).   

Small inline "booster" pumps

Small inline "booster" pumps

Vertical inline pump

Vertical inline pump

Engineers and owners typically choose a base mounted or inline pump based on:

(1) The type of installation and maintenance space that’s available

(2) The installed cost

(3) Maintenance and repair costs

(4) Operational costs and efficiency

(5) Life expectancy and total cost of ownership

(6) Whether the installation is in a geographical area that is at a high risk for seismic activity. It should be noted that such areas are not limited to the west coast, but other areas of the country as well, such as Charleston, SC and Memphis, TN.

Seismic Concerns

 In areas with a higher instance of seismic activity, in-line pumps are at greater risk for what is known as an overturning moment or OTM.  OTM refers to the point at which a specific rotational force becomes great enough to cause an object to tip over or overturn. Obviously, inline pumps don’t “tip over,” but seismic forces can magnify their rotational movement, resulting in a twisting effect on the piping and placing higher than acceptable stress on the pump flange and bolts.   Base-mounted pumps have a low center of gravity and therefore are at a negligible risk for OTM.

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