Page 287 - Intro Predictive Maintenance

278 An Introduction to Predictive Maintenance

viscous materials generally have a higher specific gravity. Reference books, like Inger-
soll Rand’s Cameron’s Hydraulics Databook, provide these values for many liquids.

The TDH can be directly measured for any application using two calibrated pressure
gauges. Install one gauge in the suction inlet of the pump and the other on the dis-
charge. The difference between these two readings is TDH.

With the actual TDH, flow can be determined directly from the hydraulic curve.
Simply locate the measured pressure on the hydraulic curve by drawing a horizontal
line from the vertical axis (i.e., TDH) to a point where it intersects the curve. From
the intersect point, draw a vertical line downward to the horizontal axis (i.e., flow).
This provides an accurate flowrate for the pump. The intersection point also provides
the pump’s efficiency for that specific point. Because the intersection may not fall
exactly on one of the efficiency curves, some approximation may be required.

Installation
Centrifugal pump installation should follow Hydraulic Institute Standards, which
provide specific guidelines to prevent distortion of the pump and its baseplate. Dis-
tortions can result in premature wear, loss of performance, or catastrophic failure. The
following should be evaluated as part of a root-cause failure analysis: foundation,
piping support, and inlet and discharge piping configurations.

Centrifugal pumps require a rigid foundation that prevents torsional or linear move-
ment of the pump and its baseplate. In most cases, this type of pump is mounted on
a concrete pad with enough mass to securely support the baseplate, which has a series
of mounting holes. Depending on size, there may be three to six mounting points on
each side.

The baseplate must be securely bolted to the concrete foundation at all of these points.
One common installation error is to leave out the center baseplate lag bolts. This
permits the baseplate to flex with the torsional load generated by the pump.

Pipe strain causes the pump casing to deform and results in premature wear and/or
failure. Therefore, both suction and discharge piping must be adequately supported to
prevent strain. In addition, flexible isolator connectors should be used on both suction
and discharge pipes to ensure proper operation.

Centrifugal pumps are highly susceptible to turbulent flow. The Hydraulic Institute
provides guidelines for piping configurations that are specifically designed to ensure
laminar flow of the liquid as it enters the pump. As a general rule, the suction pipe
should provide a straight, unrestricted run that is six times the inlet diameter of
the pump.

Installations that have sharp turns, shut-off or flow-control valves, or undersized pipe
on the suction side of the pump are prone to chronic performance problems. Such