2202MYJE-MY-C8-N_2018.02.
Chapter 4 Operation of Compressor and Unit
Compound 2-stage Screw Compressor 3225**C 4.1 Lubricating Oil (Refrigerant Oil)
4-1
Chapter 4 Compressor and Package Unit Operation
4.1 Lubricating Oil (Refrigerant Oil)
Lubrication management is very significant to keep the compressor in a good operating condition.
Take the following notes when managing lubricating oil.
4.1.1 Precautions for Selecting the Lubricating Oil
Selection of the lubricating oil should depend on the type of the refrigerant, the type of the
evaporator used with the compressor, and the conditions under which the compressor is
operated. Also to be considered when selecting lubricating oil are the properties of the oil that
include not only the viscosity but also such characteristics as compatibility in refrigerant,
separability from refrigerant, low temperature fluidity, high temperature thermal stability, etc.
We therefore recommend contacting our sales offices or service centers for choice of a
specified brand for your system.
Lubricating oil used for compressors must have a viscosity appropriate for lubricating the
bearings and other components in the compressors. The viscosity to be considered in this case
should be the viscosity the oil shows at the oil inlet of the compressor. The viscosity of the
lubricating oil significantly changes depending on the type of the refrigerant used in combination
with the oil. If the refrigerant dissolves in the oil (or the oil and refrigerant are compatible), the
viscosity of the oil drops to a level remarkably below the level required for operation of the
compressor under some operating conditions. On the contrary, if the refrigerant does not
dissolve in the oil (or the oil and refrigerant are incompatible), the viscosity may become too high
when the supply oil temperature is low. For this reason, the lubricating oil must be selected such
that it is supplied to the compressor with an appropriate viscosity (kinematic viscosity of 13 to 40
mm
2
/s) in the operating state.
The circulation of the lubricating oil for the entire system must be considered. After lubricating
and cooling each part of the compressor, the lubricating oil is discharged with refrigerant gas.
Most of the oil which is discharged from this compressor is trapped by the oil separator and is
cycled to the compressor. A small quantity of refrigerant oil goes to the condenser and the
evaporator. The lubricating oil is required to have sufficient fluidity and stability inside each part
in the refrigerating cycle where temperatures differ.
Note that some lubricating oils cannot be used depending on the combination with the
refrigerant. The following caution is an example case that is required especially attention.
Be careful since polyolester synthetic oil (POE) must not be used with ammonia
refrigerant.
4.1.2 Recommended Lubricating Oils
When selecting lubricating oil, not only compatibility with refrigerant but also effects on O-rings must be
considered. To prevent compressor malfunctions, we recommend the lubricating oil described below.
4.1.2.1 Recommended Lubricating oils for Ammonia Refrigerant
Polyalkylene Glycols (PAG) Based Synthetic Oil (compatible oil)
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