Vibrations and sound

Compressor vibrations and pressure pulsations are normally very low by design. However, they can evoke resonance frequencies in piping and heat exchangers (i.e. meet the natural frequency of the system), which results in system sound, vibration, and potentially in piping fatigue and leakage. Possible sources of vibrations are:

• pressure pulsations in the discharge gas line
• torque fluctuations acting on the compressor mountings or on the flanges of line connections
• resonances with the economiser line

The specific vibration characteristics may result in sound emission, which in the case of an unfavourable pipe layout can be transmitted to the housing or building elements via the suction and discharge gas piping. Rotating and tilting movements during start and operation may occur additionally. Therefore, the pipes must be sufficiently flexible and insulated against vibrations at the fixing points.

Critical pipe lengths whose natural frequencies are in resonance with the compressor pulsations must be avoided (±15% of critical pipe length). The calculation must at least consider the operating conditions, the refrigerant (sonic speed), and the pulsation frequency of the compressor: The base frequency of Orbit compressors is approx. 48 Hz (50 Hz network) or 58 Hz (60 Hz network). Frequencies of higher orders (96 / 192 Hz or 116 / 232 Hz) should also be checked in the final layout.

The whole system, particularly the pipes and capillary tubes, must be checked for abnormal vibrations. The pipes should be flexible enough to allow normal starting and stopping of the compressor without exerting excessive stress on the pipe joints. If required, take additional safety measures. For special considerations regarding vibrations with external frequency inverter:

• EST-420: Bitzer scroll compressors with external frequency inverters

Data from sound measurements for each compressor is provided in the Bitzer Software, tab "Technical data", and in:

• AT-340: Sound data for BITZER compressors