Compressor Oil Return, Oil Balancing And Floodback Tests - Emerson Copeland Scroll YH04K1E Application Manuallines

3.14 Compressor oil return, oil balancing and floodback tests

CAUTION
Inadequate lubrication! Bearing and moving parts destruction! Ensure
adequate oil return from the system into the compressor at any time. No liquid
refrigerant return to the compressor. Liquid refrigerant dilutes the oil, could
wash the oil off the bearings and moving parts and could lead to overheating
and compressor failure.
The system piping must be carefully designed to ensure sufficient refrigerant gas velocity, so that oil
returns to the compressor at all times and conditions. Individual piping diameter calculation depends
on the refrigerant properties, pressure level, mass flow, and density.
Once a new system design is set and assembled, a functional test and verification is required. The
functional test includes a qualification for the general system oil return and a refrigerant floodback
test. Systems with multiple compressor applications (two, three, or more) require additional oil
balancing qualification between the parallel compressors.
A sample compressor equipped with an external oil sight tube can be ordered from Emerson for lab
testing.
Records of the evaporating temperature and the bottom shell temperature shall be taken with a high
sampling rate during the entire oil return or oil balance testing and under all tested conditions. The
liquid level in the sight tube has to be observed and recorded too. Testing conditions shall include
defrost and varying loads. If the system is reversible, the tests should be conducted in both operation
modes.
System engineers should review the system design and operation to identify the critical conditions
and to check oil return, oil balancing and liquid floodback. Typically, the following situations should
be considered:
▪ In single compressor systems: to check oil return, testing conditions shall be at minimum mass
flow and minimum density of suction gas in continuous and frequent start-stop-cycling.
▪ In multiple compressor systems: to check oil return and oil balancing in the tandem or trio,
testing conditions shall be at the corner points of the system application envelope in continuous
and frequent start-stop-cycling.
▪ In all systems: to test liquid floodback, all possible transient operation conditions in the system
should be checked, eg, compressor frequent start/stop, compressor start after long off time with
migration, defrost, switching between the operation modes in reversible systems, load changes,
fans or pumps cycling at low load and more. To evaluate the risk of liquid floodback, please refer
to the oil dilution chart in
checked.
Figure 13: Oil dilution chart (tb = bottom shell temp.; te = evaporating temp.) and oil temperature
The bottom shell temperature together with the evaporating temperature gives an indication whether
liquid refrigerant is returning or diluted in the compressor oil sump. The compressor sump
temperature must remain in the (green) safe area, as shown in the oil dilution chart – see Figure 13
AGL_HP_ST_YHK1E_E_Rev02
Figure 13. Liquid level and superheat at compressor inlet have to be
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