How much vibration in an air compressor is considered abnormal? Common causes, monitoring parameters, and troubleshooting methods.

How much vibration in an air compressor is considered abnormal?

To determine whether the vibration of an air compressor is abnormal, one typically refers to the standards published by the International Organization for Standardization. ISO 10816 series standards or relevant national standards. Vibration assessment is not based on a single numerical value; rather, it is closely related to the equipment’s rotational speed, power, and support type. In general, vibration intensity—defined as the root-mean-square value of vibration velocity—is the primary indicator for evaluating the vibration condition of rotating machinery.

For standard industrial air compressors, the root-mean-square (RMS) vibration velocity is generally considered acceptable or within normal operating limits when it remains within a specified range. An abnormal vibration condition is identified when the RMS vibration velocity exceeds the manufacturer‑set threshold or exhibits a significant sudden increase—such as more than doubling—relative to the initial baseline value. Furthermore, if the equipment produces noticeable periodic impact noises during operation or experiences an unusual rise in temperature, even if the absolute values do not exceed the allowable limits, these symptoms should trigger caution and prompt thorough inspection.

Common Causes of Abnormal Vibration in Air Compressors

The causes of abnormal vibration in air compressors are diverse and can be primarily attributed to the following factors:

• Rotor imbalance:Dirt adhering to the impeller or rotor surface, uneven wear, or manufacturing and installation errors can cause the center of mass to misalign with the axis of rotation, generating centrifugal forces that induce vibration.
• Shaft misalignment:When the motor is connected to the compressor’s main shaft, parallel misalignment or angular misalignment can occur, leading to significant additional bending moments and vibrations during operation.
• Bearing wear or damage:Fatigue spalling, excessive clearance, or inadequate lubrication in rolling or sliding bearings can lead to unstable operation and high-frequency vibrations.
• Foundation loosening or resonance:Loose anchor bolts, insufficient foundation stiffness, or a close match between the equipment’s operating frequency and the structure’s natural frequency can trigger resonance.
• Airflow Pulsations and Pipeline Vibration:The characteristic flow pulsations of reciprocating compressors can excite resonance in the piping system, leading to increased vibration of the entire compressor unit.

Key Vibration Monitoring Indicators

In condition monitoring and fault diagnosis, three vibration-based metrics are typically employed to comprehensively assess equipment health:

• Vibration displacement:It primarily reflects the rotor’s low-frequency vibrations and is commonly used to assess the clearance and relative vibration of rotors in large, low-speed compressors supported by sliding bearings.
• Vibration velocity:The core indicator of vibration intensity, which is most sensitive to medium-frequency vibrations, is the preferred parameter for assessing the overall vibration condition of most medium- and high-speed air compressors.
• Vibration acceleration:It is highly sensitive to high-frequency impact signals and is commonly used to detect early-stage localized defects in rolling bearings, gear meshing anomalies, and other high-frequency faults.

Methods for Troubleshooting and Addressing Abnormal Vibrations

When encountering abnormal vibrations, troubleshooting should follow the principle of “external first, then internal; simple first, then complex.”

• Basic and Connectivity Checks:First, check whether the anchor bolts are loose and whether the pipe supports are secure, and eliminate vibrations caused by external mechanical looseness.
• Reconciliation of accounts:Using precision instruments such as laser alignment devices, recalibrate the coaxiality between the motor and the main machine under the specified hot‑ or cold‑state conditions.
• Rotor dynamic balancing:If spectral analysis indicates that the vibration frequency matches the rotational speed and the phase remains stable, on-site dynamic balancing or factory‑return static/dynamic balancing correction of the rotor is required.
• Bearing and Lubrication System Inspection:Check the lubricating oil’s pressure, temperature, and quality; if necessary, assess bearing condition via vibration spectrum analysis, and replace any damaged bearings promptly.
• Airflow Pulsation Control:For reciprocating compressors, airflow pulsations can be mitigated and pipeline vibrations reduced by installing orifice plates, optimizing piping layouts, or adding surge tanks.