For refrigeration system that use expansion valves, bac […]
For refrigeration system that use expansion valves, backwashing and expansion valve selection and improper use are closely related. Expansion valve selection is too large, the superheat setting is too small, the temperature package installation method is not correct or insulation bandage damage, expansion valve failure may result in back to liquid.
For small refrigeration systems that use capillaries, overfilling may cause backflushing. Evaporator frosting serious or fan failure heat transfer worse, non-evaporated liquid can cause back to liquid.
Frequent fluctuations in temperature can also cause expansion valve malfunction caused by back to liquid. For refrigeration systems where backwash is more difficult to avoid, installing a gas-liquid separator and using pump-down shutdowns, which allow the compressor to drain the liquid refrigerant in the evaporator before shutting down, can effectively prevent or reduce the risk of backwashing.
Back to the air-cooled compressor at start-up, the crankcase of the phenomenon of intense foaming of the lubricant is called liquid start. Blistering at start-up with liquid can be clearly observed on the oil sight glass. The basic reason for starting with liquid is that a large amount of refrigerant dissolves in the lubricant and sinks below the lubricant, suddenly boiling when the pressure suddenly drops, and causes the foaming of the lubricant. The duration of blistering depends on the amount of refrigerant, usually a few minutes or ten minutes. A lot of bubbles floating on the oil surface, and even full of crankcase. Once ingested into the cylinder through the intake port, the foam will be reduced to liquid, it is easy to cause liquid impact. Obviously, the liquid attack caused by the start of the liquid only occurs during the start-up process.
After the compressor is shut down, the temperature will decrease and the pressure will increase. Due to the low partial pressure of the refrigerant vapor in the lubricant, it absorbs the refrigerant vapor on the oil surface, causing the crankcase pressure to be lower than the evaporator pressure. The lower the oil temperature, the lower the steam pressure, the greater is the absorption of the refrigerant vapor. The vapors in the evaporator slowly "migrate" to the crankcase. In addition, if the compressor is outdoors, in colder or at night temperatures tend to be lower than in-home evaporators, the pressure in the crankcase is low and the refrigerant is also easily condensed into the lubricant after it has been transferred to the compressor.