High Vibration at 1.5X in electrical motor

Hello everyone,

I measured the vibration in the vertical direction of the electrical motor (1800 rpm) shown in the picture below. And the spectrum showed a high peak at exactly 1.5X.

Someone could tell me what problem it should be?

Thank you



Photos (2)
Original Post

300 rpm for Homogenizer is 0.3333 x motor speed (300/1800)

Vibration at 1.5 x motor shaft speed is a symptom of looseness from motor rotation speed. Possible locations for looseness include: shaft bearings, cabinet base at floor/foundation, motor base, homogenizer base, pipes connected to homogenizer and cabinet. 

Since homogenizer runs at or near 0.333 x motor speed, the vibration at 1.5 x motor speed would be nearly equal to 4.5 x homogenizer speed. Cannot rule out either mechanical (looseness) or pulsation excitation from homogenizer.

The dominant frequency is 1.5 x motor speed or 45-Hertz. There may be  a structural natural frequency in vertical direction that amplifies vibration levels. An impact test could confirm or rule out this issue.

The vibration level is low, so unless it has increased by about a factor of two or homogenizer output is abnormal, I would take no action (except as indicated); other than routine monitoring.

Basic actions can include: inspect/test for component looseness, impact test for natural frequency, inspect belt and sheave condition, measure-correct sheave alignment and belt tension, measure high frequency vibrations for bearing condition, check process pressure and flow for low output (or poor product quality), and indications of unusual pulsation and pipe vibrations.

Please provide a response to your follow-up actions.


Dear Walt, FBurgos,

We are gonna make routine monitoring, because I also think that it is a low level vibration.

The parameters of instalation are good as recommended by manufacturer.

what makes me surprise were both peaks higher than 1x. Any way, we are gonna look how does it change over time.

Thanks both of you.


Walt, totally agree, investigation steps would include searching for structural resonance, on the other hand reviewing my math

homogenizer running speed is 600/1800=1/3=0.333x

piston discharge frequency is 600*3/2=900 rpm or 900/1800=0.5x therefore i think it could be normal operation for the Homogenizer to show this frequencies.

the third harmonic of piston discharge frequency (900*3=2700) is 1.5x motor speed

a very odd combination 

why i was thinking harmonics of 300rpm must be all around, well something like a fourstroke motor where 0.5x harmonics are dominant... is it the same?


I have not worked on a Homogenizer, but I did some online searching. There is a good possibility that the Homogenizer has an internal gearbox (like some blowers) that further reduces speed of piston crankshaft. According to this excerpt from a pulsation damper supplier, the pulsation frequency is at 3x crankshaft speed (not necessarily at input sheave speed).

"the most frequently used homogenizer type with 3 pistons delivering 12000 liters per hour has been used as a reference in the below detailed discussion:

The peak delivery from a 12000 liter per hour homogenizer as the piston delivery is at its highest is almost 14000 liters per hour and the lowest is approx. 8,300 liters per hour.

With 3 pistons, this takes place 3 times per revolution and as the RPM is 165, it happens 495 times per minute and at a frequency per second: 8.25 Hz.

Each dip happens over approximately 100 angular degrees of a revolution, so that the accumulated volume must be absorbed over the first 50 degrees and returned to the flow in the next 50 degrees. This gives a time frame of only 0.1 second and It is noteworthy that the overlap is a sudden change requiring the lowest inertia possible for an optimal result.

Based on the diaphragm principle (made from solid foodgrade silicone) the large membrane is divided into smaller sections. As a result, when the pressure drops and feed-compensation to the homogenizer is required, the membrane allows for a shallow depression of sections of the membrane ensuring a fast absorption of pressure and volume and equally fast response.

As the function is depending on the stretching of the material, it means that higher working pressures (max. 35 bar) makes the damper even more efficient.

An even faster response can be achieved at low-pressure ranges by pre-stressing the damper with steam or condensate."

From <http://www.dstriple.com/news/n...le-pulsation-damper/>

The OP is advised to get the machine details so that vibration analysis and fault diagnosis is accurate.


Good case study. Team members covered well in all aspects.

Please take vibrations on Homogenizer and motor NDE and DE side. When )0.5x, 1,5x and even 2.5x indicating, though the values are on lower end, the looseness is creating in the driving system.

Please look into pulley tightness and when was last tightening performed. 

Rest all others covered by Mr. Walt Strong effectively.

Request you to share once the problem identified about the looseness or else any other for this forum to elevate our credit levels.





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