Myths and Truths about Balancing

MYTH: “1x RPM is always caused by unbalance.”
TRUTH: Unbalance always causes vibration at 1x RPM.  However, 1 x RPM is not always caused by unbalance.  Many other problems can exhibit vibration at this frequency.  Examples are:  Misalignment, Bent shaft, bowed shaft, cracked shaft, eccentricity, open rotor bars in the motor, rubs, looseness, belt issues  and resonance. 

MYTH: “The run time and lifetime of the equipment can be extended by performing a balance job on the equipment.”
TRUTH: Problems such as misalignment, bad bearings, looseness, etc cannot be corrected by balancing the machine.  It is almost impossible to correctly balance a machine that has other defects affecting its performance.  Misalignment, bad bearings looseness etc should be corrected before attempting to balance equipment.

Pipe Strain is Soft Foot!

Soft foot means machine frame distortion. If you are missing shims under a foot and tighten the hold-down bolt until you have forced the foot down to the base, you will have distorted the machine frame. If you have severe pipe stress on a pump, and the anchor bolts are tight, chances are great you are also distorting the pump casing. Consider that if the pump’s anchor bolts were completely loosened or removed, the pump might be hanging in the air from the piping. So if you were now to tighten the anchor bolts, you would be forcing the pump down to the base and distorting it, just as happens when you are missing shims under a foot.

Shimming the feet will rarely solve the problem completely; rather, the correct solution is to eliminate the undesirable pipe stress. “Stress” is the force acting on something, while “strain” is the deflection or distortion resulting from the stress. A soft foot condition means you have machine frame strain, and pipe stress is just one of several examples of this. When the machine casing is distorted, the internal alignment between the bearings is changed and the shaft is deflected. This produces enormous stress on the bearings and increased vibration in your machines, resulting in premature wear and tear as well as loss of efficiency. Your seals and bearings will fail much faster. If a significant soft foot condition exists, a good alignment of the centerlines of the shaft rotation is almost pointless. The machines will still fail more quickly and lose efficiency. How do we diagnose and fix this?

The trick lies in knowing how to recognize that a pipe strain problem exists. The behavior of a machine with pipe strain differs significantly from one whose soft foot condition is caused by one of the more traditional shimming problems or unevenness of base or feet.

Any impact on the alignment of more than about 2 mils indicates a pipe strain problem that should be dealt with. Correcting pipe strain is a task for an experienced pipefitter who must see to it that connecting and torquing the piping should not move the machine from its rough aligned condition, nor distort its casing in any way. Proper pipe hanging techniques and a good knowledge of calculating and designing “Dutchman” spacers is essential.

Taken from Ludeca Blog

Understand shaft alignment fundamentals

Keeping your rotating shafts in alignment is a fundamental—and often overlooked—maintenance project. Alan Luedeking, the manager of technical support for Ludeca Inc., Doral, Fla., talked with Plant Engineering (PE) about some of the critical issues in shaft alignment, and how they affect safety, energy, and productivity.



PE: Maintenance personnel aren’t always looking for issues with shaft alignment. Are there some warning signs or performance cues that operators or maintenance staff should be on the lookout for that might indicate a problem?


Luedeking: Yes indeed. If you hear unusual noise or feel increased vibration, those are important warning signs that should not be ignored. All the senses should be involved. Smell your environment: chemical leaks, overheating grease, and unusual stains, all are diagnostic clues and warning signs. One should always be alert to everything in one's surroundings in the plant, for safety as much as for good maintenance. Most importantly, a proactive maintenance program should include condition monitoring-based strategies and solutions to prevent unnecessary repairs and unscheduled downtime in the first place.


PE: Let’s talk about the ROI of shaft alignment. When you’re out of alignment, what are the potential losses in terms of both productivity and uptime?


Luedeking: They are great. Besides the obvious risks of a broken coupling or shaft, misaligned shafts lead to increased radial load on the bearings with consequent great reduction in service life. Besides wear and tear, less obvious is that misalignment also results in increased power consumption, which several careful studies have shown to range as high as 10%, although more conservative estimates easily reach 4%. The efficiency of the machines is impacted, and product quality may be affected by the increased vibration resulting from misalignment.


PE: What’s the correlation between shaft alignment and energy efficiency? This would seem to be an overlooked area.


Luedeking: Funny you asked—I was just thinking about that in my previous answer. This aspect is often overlooked, and a savings of 4% on an energy bill of $50,000 a month easily justifies the best laser shaft alignment on the market in less than a year, without even considering the benefits of greater uptime, less repair expense, and time saved on the alignment itself.


PE: What are a few basics about shaft alignment that should be on the minds of operators and maintenance staff?


Luedeking: Safety and quality. Safety first, always. Make sure your machines are locked out and tagged out before you set up. When I say quality I refer to two things: the suitability of your laser alignment system for the task at hand, and the excellence of your alignment procedures. Are the machine bases properly designed, installed, and cared for? Always check for, analyze, and correct soft foot. Does your laser system help you do this?


Do you have jackscrews in place to move your machines? Do your millwrights have access to good-quality stainless steel shims? Are your machines under pipe strain? Can your laser system even measure that and help you find it? Are you considering thermal growth and dynamic load shifts in the positions of your machines? If not, you may be grossly misaligning your machines by aligning them to zero when cold.


Your laser system should let you input target specs, or thermal growth values at the feet, and calculate this growth from observed changes in temperature, or even measure and monitor this growth live as you run the machines! Only the best-quality laser system will let you do all of these things, thereby achieving better results and saving you time and money at every step.


Taken from Plant Engineering

Combustion Air Fan & Efficiency

In order for your boiler to operate at peak efficiency, it is important that the correct balance of fuel and combustion air is achieved. Air and fuel ratios are controlled through linkages, fans, dampers and the increase or decrease of gas pressure. Gas pressure is controlled through a pressure regulator and a fan controls the volume of combustion air.

If there are any problems with the fan, more energy may be introduced into the system, causing decreased efficiency. To help ensure that your equipment is running at its peak performance, please review the common fan problems below.

Fan Capacity/Pressure is Below Rating:
1. Dampers or variable inlet vanes are not adjusted properly
2. Fan inlet or outlet conditions are impaired
3. Multiple air leaks within the system
4. Damage sustained to the blower wheel
5. Direction of rotation is incorrect

Fan Vibration:
1. Worn bearings
2. Unstable foundation
3. Foreign material in the fan causing an imbalance
4. Misalignment of bearings, couplings, wheel or v-belt drive
5. Damaged wheel or motor
6. Bent shaft
7. Worn coupling
8. Loose dampers or variable inlet vanes
9. Speed too high or incorrect fan rotation
10. Vibration to fan transmitted from another source
11. Uneven blade wear
12. Loose or broken bolts or set screws

Overheated Bearings:
1. Improper lubrication
2. Poor alignment
3. Damaged wheel or driver
4. Bent shaft
5. Abnormal end thrust
6. Dirt in bearings
7. Improper belt tension

Overload on Driver:
1. Speed too high
2. Direction of rotation is incorrect
3. Bent shaft
4. Poor alignment
5. Improper lubrication
6. Wheel wedging or binding on fan housing

Taken from Nationwide Boiler Blog

Fault Listing for DDCC S320 for SAACKE Burner user with DDCC BMS

This fault has occurred for one of the following reasons:

F1 – Gas incorrect position
A drive positioning fault has occurred, which will cause a safety shutdown of the burner.

F2 -Oil incorrect position
During close position prove, when a drive stops at a position which is outside the close set position by more than five degrees.

F7 – Sec.air damper incorrect position
During purge position prove, when a drive stops at a position which is outside the close set position by more than five degrees

F9 – Prim.air damper incorrect position
During pre purge, ignition or post purge, when a drive moves from its set point.

F10 – Recirc.air damper incorrect position
During modulation, when a drive is not at its correct set point as defined by the commissioned fuel/air ratio for the selected profile.

F8 Variable speed incorrect position
A drive is defined as having moved from its set point if its positional error is more than 1o for 15s, or more than 5o for 1s.