Standstill bypass for oil separator

• A standstill bypass is particularly important for large compressors and systems with longer shut-off periods where there is no pressure equalisation between the high and low pressure sides during standstill.
• In systems that are switched on for a long time and where the oil cools down only slightly during the short breaks in operation (e.g. compound systems in supermarkets), a standstill bypass is often not necessary.

The standstill bypass relieves the oil separator of suction pressure after the compressor is shut off. This reduces the refrigerant saturation of the oil and maximum oil viscosity is assured for the next start. In addition, oil and refrigerant migration into the compressor are avoided. With many compressors, the standstill bypass also leads to additional start unloading.

Required components/pipe works:

• Check valve downstream of the oil separator
• Pressure equalisation line between oil separator and suction gas line
• Diameter 6 mm – 1/4''
• Controlled by solenoid valve
• Opened only at standstill – with parallel compounding, the solenoid valve may only be opened when all compressors are switched off (HS. and OS. parallel compounding)

A standstill bypass in conjunction with an automatic pump down system (Pump down system) can lead to an increased cycling rate. This must be limited to max. six starts per hour by setting the low pressure switch and the pause time (time relay). Depending on the operation mode, a single pump-down before shut-off may also be sufficient.

With CS. compressors, the oil separator is integrated in the compressor, therefore no bypass is necessary.