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Reliability
Wire by www.reliabilitydirect.com "Your
One Stop Shop for Condition Monitoring" |
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Vibration,
Balancing, Alignment, Ultrasound, Oil Analysis & more...
Volume
3, Issue # 10 - October, 2002 |
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In
this Issue: |
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New
Products: New Additions to
the RDI On-Line e-commerce catalog
Ask
The Expert: Cooling Tower Fan
Monitoring
What's
Hot: Best Selling Items form the
RDI On-Line Catalog (Over 700+ products)
Recommended
Book: Maintenance
Planning and Scheduling Handbook
by Richard
D. Palmer
Contest
Winner: Thomas
Hoops - Howden Compressors, LLC |
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New
Products: |
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We
offer over 30 different models of Ultrasonic Wall Thickness & Coating
Thickness gauges. From basic units to more sophisticated data logging,
multi-function gauges. Check out the new index of these quality
instruments: http://www.reliabilitydirect.com/ultrasoundproducts/thicknessindex.htm
The
CMCP-SHAKER
is a Low Cost portable vibration calibration tool, with variable frequency
and variable amplitude capabilities. The CMCP-SHAKER has a built-in
reference accelerometer that is traceable to the National Institute of
Standards and Technology (NIST). The system complies with API670 and OSHA
1910. It also conforms to the ISO9001 quality standard.
We
have expanded our offering of Accelerometers, Cables, and Mounting
Accessories. Take a look at our index for the variety of sensors, cables,
epoxy, magnets, etc. that are available from Reliability Direct. http://www.reliabilitydirect.com/accelerometeraccessories/accelerometerindex.htm |
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Ask
The Expert: Cooling Tower Fan Monitoring |
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Cooling
Tower Fans have applications in all industries. They remove heat from
other materials, usually water. A cooling  tower
may consist of one cell or many individual cells in a single structure. A
single plant may have multiple structures. Cooling Tower Fans come in two
basic types. The first type has the motor mounted to the side of the cell
and uses a jackshaft to drive the gearbox in the center. The second type
has both the motor and gearbox centrally mounted in the cell. The
mechanical components of a Cooling Tower Fan are made up of, Motor,
Jackshaft (Optional), Gearbox, and Fan Blades.
The motor speed for
a Cooling Tower Fan is usually 1800 RPM. Fan speeds are much slower and
determined by the diameter of the blades to keep the blade tips subsonic.
Average cells are 14 feet to 28 feet in diameter. Fan speeds of 90 to 230
RPM are normal for cooling tower fans. In cooler climates, the fans can be
reversing to prevent freeze during the winter.
The most common
Cooling Tower Fan failure involves the gearbox or fan blades and are
catastrophic in nature. In many cases, this type of failure leaves the
gearbox and fan blades lying in the cooling water pond at the bottom of
the tower.
Many Cooling Tower Fans were equipped by the OEM
(Original Equipment Manufacture) with a
earthquake detection type devices mounted close to the cell. Although
questionable to start with for this application, over time most of these
devices have quit working due to corrosion or neglect.
Permanent monitoring is the recommended solution for
preventing cooling tower cell failures. Periodic measurement programs
rarely produce the desired result. In most cases, the location and
environment discourages any attempts to take data or visually inspect the
fan.
Permanent monitoring of a cooling tower fan cell
requires direct monitoring of the most important component by mounting a
transducer directly on the gearbox. Additional system protection can be
added by mounting transducer(s) to the motor. Additionally, knowledge of
the expected vibration frequencies is important.
1. Fan Speed 90-300 RPM
2. Blade Pass (Fan Speed X # of Blades)
3. Gear Mesh Frequencies
4. Motor Speed
5. Bearing Frequencies
Gear Vibration
The central component of a cooling tower is the
gearbox. This is often a high maintenance source due to aerodynamic
loading from the fan, excessive loading on the gear teeth, and improper
alignment of the gear to the motor.
The gearbox is always located within the cooling water
stream requiring special consideration for mounting a vibration sensor.
The environment is usually caustic due to chemicals added to control the
pH level of the cooling water.
A vibration sensor must be able to measure the expected
gear mesh frequency, blade passage, and bearing defect frequencies. Other
frequencies of interest include fan balance and motor alignment.
Gear and bearing defect frequencies tend to be the
highest frequencies, while the fan balance frequencies are the lowest to
be monitored. The other frequencies are found scattered between these
extremes.
Monitoring the gearbox can be accomplished by
installing a single low frequency accelerometer (793V)
on the gearbox in a horizontal orientation perpendicular to the jackshaft.
The output signal should be routed to CMCP500 Series Monitors. One monitor
should be specified to measure velocity for higher frequencies like gear
mesh. The second monitor should be specified to integrate the signal to
displacement terms for lower frequencies such as blade speed and blade
pass.
(1) 793V Accelerometer 100mV/In/Sec Output.
(1) CMCP602H-32-02-01 Armored Extension Cable.
(1) CMCP200-01 Mounting Pad 1/4"
(1) CMCP230 Mounting Stud
(1) CMCP220 Acrylic Adhesive Bypac
(1) CMCP530-100V-02P-00-00 Velocity Monitor
(1) CMCP535-100V-30-00-00 Displacement Monitor
Motor Vibration
Motor vibration frequencies of interest include motor
unbalance, rotor bar defects, output shaft alignment, and bearing defect
frequencies. A complete continuous monitoring approach should include one
accelerometer per bearing location. Mounting orientation for the
accelerometers should be horizontal at the bearing. As the motor speed is
usually 1800 RPM economical standard accelerometers such as the 786A
can be used. A more economical approach would be to mount a single
accelerometer at the motor output shaft bearing location only.
(2) 786A Industrial Accelerometer
(2) CMCP602H-16-02-01 Armored Extension Cable
(2) CMCP200-01 Mounting Pad 1/4"
(2) CMCP230 Mounting Stud
(2) CMCP220 Acrylic Adhesive Bypacs
(2) CMCP530-100A-02P-00-00 Velocity Monitor
Start Up Considerations
All CMCP500 Series Monitors are provided with relays,
reset terminals and a trip multiply function. Cooling Tower Fans
experience large amounts of vibration during start-up. Either timer logic
or a contact to energize trip multiply needs to be provided if the
monitors are wired to shutdown.
DCS/PLC Systems
The CMCP500
series monitors can be equipped with Modbus or TCP/IP communications.
I/O can be specified to provide operators with vibration levels, alarm set
points, discrete alarms and the ability to energize the trip multiply and
reset functions. A complete system using Modbus or TCP/IP can be specified
providing operators with screens and software. |
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What's
Hot: |
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With
an optional photo-tach or laser-tach, the Bal
Pac 1200 Vibration Analyzer becomes a portable balancing system. Upon
completion of the easy 2-step or 3-step calibration process, the unit can
display both amount and angle of force or dynamic unbalance, respectively.
The user can select either English or metric units of unbalance, including
oz-in, ft-lb, g-mm, g-cm, kg-mm, Newton-meters or mass at a selected
correction radius. Included in the balancing software is a segmenting
program, which displays the amount of correction required in two adjacent
work-piece segments. This allows the operator to easily balance
work-pieces without a continuous correction surface, such as fans.
The
PK2
Pocket Strobe remains our best selling stroboscope, offering new
improved performance at a low price. Now CE certified, the PK2 is 300%
brighter than PK1, has a flash rate of up to 12,500 flashes per minute and
a longer-lasting flash tube. The PK2 is lighter than the PK1 and has an
internal NiMH battery that provides a full hour of continuous operating
time regardless of flash rate.
Our
best selling IR Thermometer remains the MT4
MiniTemp. The MT has proven applications in HVAC, Automotive and
hundreds of uses at work or around the home. MINITEMP™—priced
to fit any toolbox and small enough to fit in your pocket. |
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Recommended
Book: This
month's 5 Star Recommendation |
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Maintenance
Planning and Scheduling Handbook by
Richard D. Palmer
This
month's 5 Star selection provides a valuable reference for the Maintenance
and Plant Manager, demonstrating how planning fits into maintenance, what
principles make it work, and how to execute your planning. The book
explains how work order planning leads to increased crew productivity and
greater overall effectiveness. One of our most popular books! |
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Contest
Winner: Thomas Hoops - Howden Compressors, LLC |
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September
Question #25: The new and improved PK2
Pocket Strobe has a flash rate of up to
12,500 per minute. |
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October
Contest Prize: Craftsman
14.4 volt Cordless Drill/Driver with Worklight!
October
Question #26: The TI-25M
can be used in a ______ _________ _______
mode or in a ____ mode ,
where the probe is dragged over a large measuring area.
Send
your answer to dgallagher@ghg.net,
subject: Question # 26. |
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