Familiarise with High Pressure Terminology

Compressor Dictionary - M

Multi-stage Compression

A gaseous medium is compressed from atmospheric pressure to final pressure in several stages, usually three or four pistons that are connected in series.

Three stage compression	Four stage compression

During compression, gases emanate heat. Hence, the medium has to be cooled between the compressor stages. BAUER's inter- and after-coolers are designed to reduce the medium's temperature to 5 - 15 °C above ambient temperature. The lower the compression ratio between the stages, the less thermal energy is emitted (see diagram above).

For 5-HP-units work well with three compression stages. For larger units, we recommend four stage units.

Diving Compressors

For optimum free air delivery, compression ratios have to be kept low. Hence, three and four-stage designs dominate for 220 and 330 bar diving compressors. Inter-coolers further reduce air temperature. These measures improve the compressor's efficiency and avert thermally induced damage to the compressor system (stress fractures, for example).

Single stage compression from 0 to 200 bar generates temperatures that are sufficiently high to cause the » lubricant to combust spontaneously in the compression chamber. High compression temperatures may also cause the oil to oxidise, thereby reducing the oxygen level and raising the proportion of carbon monoxide and dioxide.

In response, the accident and hazard prevention guidelines (Unfallverhütungsvorschiften UVV16 - Verdichter) quotes a maximum compression temperature of 160 °C. Consequently, permissible compression ratio cannot exceed 1:9. For large compressors, much thermal energy needs dissipating. Therefore, four stage compressors are favoured. The addition compressor stage lowers the compression ratio to 1:3 or 1:4.

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