Rotary Screw Compressor Vibration Monitor

Per ISO 10816, up to 1.4 mm/s RMS is new-machine condition (zone A) and up to 2.8 mm/s is acceptable for unrestricted long-term operation (zone B). Between 2.8 and 4.5 mm/s the machine should be scheduled for corrective maintenance (zone C), and above 4.5 mm/s vibration is severe enough to cause damage (zone D).

A steady multi-month rise at the airend housing, often with rising discharge temperature and falling efficiency (more kW per m³/min). Airend bearings rarely fail suddenly; they telegraph over months. Plan the overhaul/exchange when the trend leaves zone B — an exchange airend is far cheaper than a seized one.

On the airend bearing housings and the motor drive-end, horizontal — as close to the bearing as possible, on stiff metal (never on covers or guards). Take horizontal, vertical and axial readings if you can; use the highest for the ISO grade and always re-measure at the same spot, load and speed.

The usual suspects are rotor contact or timing-gear wear in the airend, coupling misalignment, motor bearing wear and discharge-pulsation driven panel resonance. A frequency spectrum tells them apart: imbalance shows at 1× running speed, misalignment at 2×, bearing defects at non-synchronous frequencies, and looseness as a raised noise floor with harmonics.

Velocity in mm/s RMS, 10–1,000 Hz. ISO 10816 zone tables are defined on broadband RMS velocity because it weights low- and high-frequency faults evenly for general machines. Acceleration (g) suits high-frequency bearing analysis and displacement (µm) suits low-speed machines, but neither maps onto these zone boundaries.