Hussmann Ingersoll Rand, User Manual

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Mechanical Design 3
Lubrication
IR Impact
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compressors are supplied with two types of lubrication systems. C-Series
compressors with the letters S or T in the model number have an Enhanced Centrifugal
Lubrication system with no oil pump, while C-Series models with the letters P or Q in the model
number, and all B-Series compressors have oil pumps.
In the past, refrigeration compressors with horizontal shafts were often designed with positive
displacement lubrication, especially larger compressors with a rated motor power larger than 5
kW. An enhanced centrifugal lubrication system has been developed, which has proven to be
highly efficient and have many advantages.
In refrigeration compressors, as in all piston machines, the lubricant serves many functions:
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Lubrication: Transfer of energy, sufficiently separate surfaces (minimize friction)
x
Cooling: Less for HFC refrigerants
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Cleaning: Keep sliding faces clean, dispose abrasion
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Sealing: Reduce leakage rate in compression chamber
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Damping: Reduce noise development and transmission
For all contact compression processes and bearings it is assumed that the application of oil
lubrication increases the machine’s durability at least tenfold, compared to dry operation. In the
case of refrigeration compressors it should be considered that the absence of oxygen within the
refrigerant circuit reduces the compressors’ wear significantly.
Oil Pump Compressors
Figure 1 shows an IR Impact
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C-Series compressor with positive displacement lubrication. The
oil is taken from the oil sump by a positive displacement pump (in this case an internal gear
pump) and discharged into the circuit. All bearings are supplied by means of bores in the shaft.
The lubrication of the slide bearings is based on the principle of hydrodynamics. As is generally
known, presence of oil at the bearing inlet is sufficient; pressure in the bearing is generated
proportionally to the load by means of an oil film. The pressure is about 50 to 150 times higher
than that of an oil pump.
In order to avoid excessive discharge pressures, the pump is equipped with a pressure relief
valve; to monitor the circuit, an oil differential pressure switch may be installed; usual discharge
pressures vary from 30 to 60 psig. In case of an oil shortage, the oil pressure switch ensures the
compressor is shut-off and an alarm output is provided.