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Vibration is everywhere! Vibration is a “back and forth” movement of a structure or component. Vibration can also be referred to as a “cyclical” movement. It can be inherent in a piece of equipment or can be induced by another form of energy. The real question is whether the vibration is detrimental to the equipment and its internal components.

Vibration is typically monitored through some form of analyzer, either online or offline such as the VIBWORKS analyzer.

What causes vibration? Here are just a few causes, but there are so more which can lead to elevated vibration levels. More importantly, if caught early enough, they can be corrected and thereby maximize the life of our equipment:

  • Installation of the machines
    • An improperly mounted bearing can cause severe vibration. This can lead to damage of the bearing as well as other components within the machine.
  • Operation of the machine
    • Pushing our machine beyond its recommended maximum output. Our machines respond by vibrating more than the recommended allowable limits and will eventually fail.

Watch our video ‘What’s Misalignment’ to learn more about the causes and effects of having misalignment in your rotating equipment

Some common machine problems that generate mechanical vibration:

  • Misalignment
    • Misalignment is one of the most common issues that leads to high vibration and eventually failure of the machine. It can be easily detected and corrected. Take the time to laser align machines properly to the recommended tolerance.
  • Unbalance
    • Unbalance is another easily missed problem that causes severe damage to our equipment. It can also lead to cracks of the housing itself. If not detected and corrected soon enough it can lead to dangerous catastrophic failure. Unbalance can be easily detected and corrected extending the life of equipment.

We never have enough time to do things right the first time but always find time to do them again.”

These few issues can be easily detected with properly set-up software. Often, the setup is incorrect and inaccurate. Invalid data is captured in the FFT. Please consult an expert to make certain you are utilizing your condition monitoring software to its fullest potential. Remember… If it’s Critical and Rotates it should be Aligned, Balanced and Monitored.

by Ana Maria Delgado, CRL

May 2016 · Plant Services Magazine
Like a lot of reliability engineers, Joe Anderson, former reliability manager at the J.M. Smucker Co., appreciated – in theory – that precise pulley alignment is critical to preventing vibration problems and ensuring successful operations.

My understanding was, ‘Yeah, we need to do it,’ ” Anderson says. “But you always have these excuses.”

When the Smucker’s plant at which Anderson worked launched a dedicated vibration monitoring and control program a year-and-a-half ago, though, Anderson quickly became a convert to making precision alignment a priority.
The plant purchased a vibration analyzer (VIBXPERT) and laser alignment tool (the SheaveMaster Greenline) from Ludeca to help aid in identifying machine defects that appeared to be linked to vibration caused by misalignment. Laser alignment allowed for correcting vertical angularity, horizontal angularity, and axial offset – the three types of misalignment – simultaneously. Whoever was using the laser alignment tool, then, could be sure that adjustments made to correct one alignment problem didn’t create an issue on another plane.
Read entire article to learn how J.M. Smucker Co. made precision alignment a priority: Get your alignment in line: Don’t jiggle while you work

by Ana Maria Delgado, CRL

Smith Pump Company recently was called to a pump station to solve a problem with high vibration on three 350HP vertical turbine pumps. The pump station was fairly new and had only been in operation for a year or two. Two of the three pumps were operated on a variable frequency drive (VFD).  The first step we performed in the field was a bump test. A bump test measures the unit’s natural frequency and is very important on a vertical turbine. The unit, mainly the vertical motor, will vibrate the most when it runs at its natural frequency. For example, if you measure the unit’s natural frequency to be 1800 cpm and the pump’s speed is 1800 rpm, you will have high vibration. To save time, we will only present the data for Pump #2. The bump test for Pump #2 measured in line with discharge was 1500 cpm. Pump #2 operates on a VFD and has a full speed of 1800 rpm. The 1500 cpm corresponds to running the pump at 50 HZ. The owner of the pump station wanted to operate the pumps between 50 to 60 HZ. After performing the bump test, we ran the pumps and measured vibration with the VIBXPERT analyzer. On pump #2 at 50 HZ, we measured 0.47 in/sec rms at the top of the motor. To compare, the Hydraulic Institute allows 0.17 in/sec rms for vertical turbine pump of this size. We knew high vibration was caused by the natural frequency of the unit based on the bump test data. On vertical turbine pumps, you can move the natural frequency up and down by making modifications to the discharge head. These particular discharge heads were built very stiff with a total of eight 1” thick stiffeners on the outside of the head body and four 3/4” thick stiffeners on the inside of the head body.
Existing Discharge Head

Solidworks Model of Existing

 
 
 
 
 
 
 
Smith Pump modeled the discharge head in Solidworks. Since the measured natural frequency was 1500 cpm, and the pump operating range was 1500 to 1800 rpm, we wanted to lower the natural frequency below 1500 cpm. We knew by removing stiffeners from the discharge head we would lower the unit’s natural frequency. We removed stiffeners and ran a finite element analysis to determine how much we would lower the natural frequency. Our model study showed that by removing all the external stiffeners and half of all the internal stiffeners we would lower the natural frequency by 30%. Pump #2 was removed and its discharge head modified by removing stiffeners.  

Solidworks Proposed Model
Discharge Head Installed Stiffeners Removed

 

 

 

 

 

 

 
Pump #2 was put back into service with its modified discharge head and vibration testing was performed. The new bump test data gave a measurement of 86 cpm in line with discharge. The vibration measured at 50 HZ at the top of the motor was 0.05 in/sec rms. The vibration dropped from 0.47 to 0.05 in/sec rms.
In conclusion, determining a unit’s natural frequency is very important when designing a vertical turbine pump. Every fabricated steel discharge head that Smith Pump makes is modeled in Solidworks and goes through a finite element analysis to make sure the unit’s natural frequency (mainly discharge head and vertical motor) is 25% away from any running speeds.  In this example, the discharge head (built by others) was too stiff and had a natural frequency at the pump operating speed causing high vibration.  Since Pump #2 was so successful, we are currently modifying Pumps #1 and #3 the same way. Common sense tells us that the stiffer and stronger the discharge head the better, but this case study clearly shows us that is not the case!
Special thanks to our customer Josh Jurgensen, service engineer at Smith Pump Company for sharing this case study with us!

by Yolanda Lopez