Vibrations

Vibrations of the compressor and pressure pulsations are usually very low. However, they can cause resonant frequencies in pipes and heat exchangers (i.e. hit the natural frequency of parts of the system), resulting in sound, vibrations and possibly fatigue and leakage of pipes. Possible sources of vibration are:

• Pressure pulsations in the discharge gas line
• Torque fluctuations acting on the compressor mounting or the flange connections of the lines
• Pressure pulsations in the economiser line

The vibrations can lead to sound emissions which, if the pipe layout is unfavourable, can be transmitted to the housing or components via the suction and discharge gas lines. In addition, rotational and tilting movements can occur when starting and during operation. Therefore, the pipes must be sufficiently flexible and vibration-damped at the fixing points.

It is favourable to lay the pipe parallel to the compressor axis, the discharge gas line should first be led downwards. The distance to the compressor axis should be as small as possible and the parallel pipe section should be more than half the compressor length. In addition, pipe bends should generally be installed with a large radius (no angles).

With hydrocarbon refrigerants, the critical pipe lengths change due to the lower density of the refrigerant. The pipe lengths must therefore be specially designed or recalculated for these refrigerants and cannot be taken directly from systems with R134a or R404A.

In case of particularly high demands on the vibration level as well as in case of longer pipe runs, a pulsation muffler should be mounted in the discharge gas line, immediately downstream of the compressor discharge.

The entire system, especially the pipes and capillary tubes, must be checked for abnormal vibrations. The pipes must be flexible enough that there is no stress on the pipe joints when the compressor is switched on and off. If necessary, take additional safety measures. For vibrations during operation with an external frequency inverter:

• ST-420: Bitzer screw compressors with external frequency inverters

For sound data on the compressors:

• AT-340: Sound data for BITZER compressors

Pulsation mufflers are available as accessories, e.g. in the ePARTS spare parts catalogue. For details, see

• DB-400: Operating instructions Muffler for discharge lines

For use of pulsation mufflers in the ECO line:

• ST-610: Economiser operation of screw compressors