Imbalance in Vertically Mounted MachinesSeverity of Imbalance
The severity of imbalance depends on both the type and size of the machine as well as the vibration level. To assess imbalance severity, average 1X levels for healthy machines of the same type should be used as a comparison. If the second order peak is as large as the first order, you should suspect misalignment.
The following levels are guidelines for general use in diagnosing imbalance for machines running at 1800 or 3600 RPM. Very high-speed machines have lower tolerance levels.
|
1X Vibration Level, VdB |
Diagnosis |
Repair Priority |
|
Less than 108 VdB
(0.141 ips)
|
Slight Imbalance
|
No recommendation
|
|
108 VdB -- 114 VdB
(0.141 – 0.282 ips)
|
Moderate Imbalance
|
Desirable
|
|
115 VdB -- 124 VdB
(0.316 – 0.891 ips)
|
Severe Imbalance
|
Important
|
|
More then 125 VdB
(>1.00 ips)
|
Extreme Imbalance
|
Mandatory
|
The measured vibration level at 1X depends on the stiffness of the machine mounting as well as the amount of imbalance, with spring-mounted machines showing more 1X than solidly mounted machines for the same degree of imbalance. The overall size of the machine also affects the allowable 1X level as follows:
|
1X Vibration Level, VdB |
Machine Type |
Repair Priority |
|
109 VdB (0.158 ips)
|
Small Single-stage Pump
|
Desirable
|
|
118 VdB (0.447 ips)
|
Large Hydraulic Pump
|
Desirable
|
|
116 VdB (0.355 ips)
|
Medium Sized Fan
|
Desirable
|
The tangential and radial 1X levels should be compared. The more nearly equal they are, the more likely that imbalance is the cause. In any case, the direction in which the machine has the least stiffness will be the direction of the highest 1X level.
Imbalance in Vertically Mounted Machines
Imbalance in Overhung Machines
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