Tank Agitator & Mixer Vibration Checker

Per ISO 10816, up to 2.3 mm/s RMS is new-machine condition (zone A) and up to 4.5 mm/s is acceptable for unrestricted long-term operation (zone B). Between 4.5 and 7.1 mm/s the machine should be scheduled for corrective maintenance (zone C), and above 7.1 mm/s vibration is severe enough to cause damage (zone D).

Physics, mostly: at low level the impeller works near the surface, drawing a vortex and loading the shaft asymmetrically — classic surface-effect vibration. Avoid sustained running with the impeller within one impeller-diameter of the surface, or add baffles/anti-vortex plates. If shaking persists fully submerged, then check shaft runout and the gearbox.

On the gearbox output (just above the tank nozzle) and on the motor — 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 bent or fouled impeller shaft, fluid forces from vortexing or off-centre flow, gearbox bearing wear, and structural softness of the tank nozzle mounting. 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.