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

470 Centrifugal Pumps: Design and Application
Table 18-5
Six-Stage Centrifugal Pump
1750 HP, 3600 RPM Variable Frequency Drive Motor
Gear Type Coupling
Dynamic Tbrques (1 Percent Zero-Peak) Applied at Motor
Maximum Resultant Torsional Stresses at 981.87 RPM
Stress
Stress
Shaft PSIP-P SCF PSIP-P
1
2
48.12
121.31
2.00
2.00
96.25
242.62
3
4
193.9?
265.92
2.00
2.00
387.93
531.84
5 336.94 2.00 673.89
6 406.63 2.00 813.26
7 474.66 2.00 949.32
8 540.76 2.00 1081.52
9 6676.68 3.00 20030,04
10 DYNAMIC TORQUE VARIATION 2489.59*
11 6822.28 3.00 20466.84
12 3763.91 2.00 7527.81
13 3087.43 2.00 6174.85
14 2359.91 2.00 4719.81
13 1599.41 2.00 3198.81
16 794.30 2.00 1588.60
* — l&lues are dynamic torque variation across coupling, ft-lbs
vibrational trend. If the vibrations show an increasing trend, the unit
should be monitored more frequently. Vibrational guidelines in common
usage can aid in determining the severity or extent of damage so that
maintenance can be scheduled. A vibrational velocity of less than 0.3 ips
(inches per second) is generally accepted as satisfactory operation for
pumps [7] and motors. Velocity levels above 0.3 ips are warnings of potential
problems. Velocity levels of 0.5 ips and above may be indicative
of significant damage to the bearings, seals, or rotor.
The basis of troubleshooting is obtaining test data on troublesome
pumps during normal operation and comparing the data to the purchase
specifications, vendor guarantees, or applicable vibration criteria. It is
crucial to the success of the troubleshooting effort to have adequate instrumentation
on the pump system. In many cases, the instrumentation
can be temporarily added to obtain the required measurements.
Measurement Techniques
Typically pumps are installed with a minimum of vibration monitoring
equipment. Some pumps may have a velocity pickup on each bearing