Maintenance Technology July 2017 - 34

VIBRATION ANALYSIS

Listen carefully. Cavitation isn't always doing the 'talking'
when you hear pump noise.

Rule out bearing noise.
To determine if the noise may be due to failing bearings, listen
on the pump volute and bearing housing. An ultrasonic listening
device is helpful, but a mechanic's stethoscope will do. If the
sound is louder on the volute than on the bearing housing, bearing noise can be eliminated as a source.
Change suction pressure.
Next, increase the suction pressure (head) if possible and listen
for a decrease in the noise. If suction head can't be increased,
reduce it and listen for an increase in noise. Cavitation is directly
related to suction head and flow, so changing either of these
should cause cavitation noise to change accordingly.

What's Your
Noisy Pump
Really Saying?
Eugene Vogel
Electrical Apparatus Service Association (EASA)

EVERYBODY LIKES a quiet pump-it just does its job, leaves
you alone, and doesn't break down often. But a noisy pump
raises concern. Although the noise is often attributed to cavitation, not every noisy pump is suffering from this problem.
Failing bearings, flow turbulence, recirculation, and even a
machine's mechanical or electrical geometry can generate
noise, any of which may be a more immediate problem than
long-term damage from cavitation.
Cavitation erodes the suction eye of the impeller without
affecting its other surfaces. Disassembly and inspection will
confirm if significant cavitation is responsible for pump noise,
but the first step is to rule out other potential causes with
non-intrusive tests.

Check for recirculation.
If suction head changes have little effect on the noise, the source
may be recirculation resulting from a discharge flow restriction,
perhaps due to a blockage or closed discharge valve. For closed
systems without flow-rate instrumentation, verifying flow may
not be easy. A portable flow meter attached to the outside of
piping will provide accurate data, but such instruments can be
expensive.
Another approach is to open a drain valve in the discharge line
near the pump and allow flow to exit the system. If this reduces
the noise at the pump, the flow through the system is very likely
restricted, and recirculation is the source of the noise. Recirculation can damage pump impellers and volutes and subjects the
pump to unnecessary vibration. Of course it's also a waste of the
energy consumed by the pump.
Determine if the noise is related to
mechanical and electrical geometry.
If changes to neither the suction head nor discharge flow alter
the noise characteristics of the pump, the sound is probably mechanical in nature. Mechanical sounds occur at specific frequencies related to the machine's mechanical and electrical geometry.
Vibration-analysis techniques can identify and characterize
these sounds and their relationship to any mechanical forces.
The most common frequency of sound and vibration in
centrifugal pumps is vane-pass frequency, which occurs at the
multiple of the number of impeller vanes and the rotating speed.
Technicians familiar with pumping machinery may well be able
to audibly separate the vane pass and other mechanical sounds
from the random noise of cavitation and recirculation.

In other words
Your noisy pump may be telling you something important. With a methodical approach and through the
process of elimination, you can translate its language and
avoid pump failure. MT

Eugene Vogel is a pump and vibration specialist at the Electrical Apparatus Service Association Inc. (EASA), St. Louis. EASA is an
international trade association of more than 1,900 electromechanical sales and service firms in 62 countries that helps members
keep up to date on materials, equipment, and state-of-the-art technology. For more information, visit easa.com.

34 |

MAINTENANCE TECHNOLOGY

JULY 2017


http://www.easa.com

Table of Contents for the Digital Edition of Maintenance Technology July 2017

Editorial
Uptime
On The Floor
Powering Auto Production
Following The North Star
Flying Inspections
Untangle Compressed Air Misconceptions
Change Your Lubrication Mindset
HMI-Design Essentials For Today's SCADA Systems
SAP: Tips and Tricks
Cybersecurity Best Practices
Bearing Storage
Interpreting IP Code
Noisy Pumps
Move From Time- to Condition-Based Lubrication
CMMS Energizes Maintenance Efforts
Products
Ad Index
Showcase
Final Thought
Maintenance Technology July 2017 - 1
Maintenance Technology July 2017 - Cover1
Maintenance Technology July 2017 - Cover2
Maintenance Technology July 2017 - 1
Maintenance Technology July 2017 - 2
Maintenance Technology July 2017 - 3
Maintenance Technology July 2017 - Editorial
Maintenance Technology July 2017 - 5
Maintenance Technology July 2017 - Uptime
Maintenance Technology July 2017 - 7
Maintenance Technology July 2017 - On The Floor
Maintenance Technology July 2017 - 9
Maintenance Technology July 2017 - Powering Auto Production
Maintenance Technology July 2017 - 11
Maintenance Technology July 2017 - 12
Maintenance Technology July 2017 - 13
Maintenance Technology July 2017 - 14
Maintenance Technology July 2017 - Following The North Star
Maintenance Technology July 2017 - 16
Maintenance Technology July 2017 - 17
Maintenance Technology July 2017 - Flying Inspections
Maintenance Technology July 2017 - 19
Maintenance Technology July 2017 - 20
Maintenance Technology July 2017 - 21
Maintenance Technology July 2017 - Untangle Compressed Air Misconceptions
Maintenance Technology July 2017 - 23
Maintenance Technology July 2017 - 24
Maintenance Technology July 2017 - Change Your Lubrication Mindset
Maintenance Technology July 2017 - 26
Maintenance Technology July 2017 - HMI-Design Essentials For Today's SCADA Systems
Maintenance Technology July 2017 - 28
Maintenance Technology July 2017 - 29
Maintenance Technology July 2017 - SAP: Tips and Tricks
Maintenance Technology July 2017 - Cybersecurity Best Practices
Maintenance Technology July 2017 - Bearing Storage
Maintenance Technology July 2017 - Interpreting IP Code
Maintenance Technology July 2017 - Noisy Pumps
Maintenance Technology July 2017 - Move From Time- to Condition-Based Lubrication
Maintenance Technology July 2017 - 36
Maintenance Technology July 2017 - 37
Maintenance Technology July 2017 - 38
Maintenance Technology July 2017 - CMMS Energizes Maintenance Efforts
Maintenance Technology July 2017 - 40
Maintenance Technology July 2017 - 41
Maintenance Technology July 2017 - Products
Maintenance Technology July 2017 - 43
Maintenance Technology July 2017 - 44
Maintenance Technology July 2017 - 45
Maintenance Technology July 2017 - Ad Index
Maintenance Technology July 2017 - Showcase
Maintenance Technology July 2017 - Final Thought
Maintenance Technology July 2017 - Cover3
Maintenance Technology July 2017 - Cover4
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