RFC SL Series Technical Manual page 31

Oil return of flooded evaporator
Flooded evaporator systems using HCFC/HFC refrigerants require independent oil return
points at the evaporator or low pressure accumulator. The oil return point (preferably more
than one) should be set in the range of the oil-rich layer at the liquid level. The oil return pipe
should be connected to the suction pipe. The refrigerant in the oil return pipe can be treated by
heat exchanger heating method. The refrigerant must be evaporated before entering the
suction pipe. There is a strong change of liquid level (for example: liquid pump system) an oil
drain point should be set at the lowest point or after the circulating oil pump.
Prevent compressor oil accumulation, fluid accumulation and start-up fluid
Special attention should be paid to piping layout and system configuration in the design to
ensure that no liquid refrigerant or lubricating oil backflow into the compressor occurs during
shutdown. For this reason, the suction and discharge ducts from the compressor should be
designed to bend downward first.
In addition, in order to prevent the compressor from starting with liquid, for the direct
evaporation system, the following additional measures should be taken:
a) Use the evaporator outlet with an upward "gooseneck";