The compressor is a complex machine that runs at high speed. Ensuring adequate lubrication of the compressor crankshaft, bearings, connecting rods, pistons and other moving parts is the basic requirement for maintaining the normal operation of the machine. For this reason, compressor manufacturers require the use of designated brands of lubricating oil and require regular inspections of the lubricating oil level and color.
Lack of oil is one of the compressor faults that are easy to identify. When the compressor is out of oil, there is little or no oil in the crankcase.
There are two ways to return oil to the compressor: one is to return oil from the oil separator, and the other is to return oil from the return pipe.
The oil separator is installed on the compressor exhaust pipe, and generally can separate 50-95% of the oil. The oil return effect is good, the speed is fast, and the amount of oil entering the system pipeline is greatly reduced, thereby effectively extending the oil-free operation time.
It’s not uncommon for cold storage refrigeration systems with extremely long pipelines, full-liquid ice-making systems, and freeze-drying equipment with very low temperatures to return more than ten minutes or even dozens of minutes after the start of the machine. A bad system will cause the compressor to stop due to low oil pressure. The installation of a high-efficiency oil separator in this refrigeration system can greatly extend the operating time of the compressor without oil return, so that the compressor can safely pass the crisis stage of no oil return after starting up.
When the compressor is higher than the evaporator, the oil return bend on the vertical return pipe is necessary. The return bend should be as compact as possible to reduce oil storage. The spacing between the oil return bends should be appropriate. When the number of return bends is large, some lubricant should be added.
The frequent starting of the compressor is not conducive to oil return. As the compressor stops for a short continuous operation time, there is no time to form a stable high-speed air flow in the return pipe, and the lubricating oil can only stay in the pipe. If the oil return is less than Ben oil, the compressor will be short of oil. The shorter the operating time, the longer the pipeline, the more complex the system, and the more prominent the oil return problem
During defrosting, the temperature of the evaporator increases and the viscosity of the lubricating oil decreases, making it easy to flow. After the defrost cycle, the refrigerant flow rate is large, and the retained lubricating oil will return to the compressor in a concentrated manner. Therefore, the frequency of the defrost cycle and the duration of each time must be carefully set to avoid large fluctuations in the oil level or even oil shock. When the refrigerant leaks too much, the air return speed will decrease. If the speed is too low, the lubricating oil will stay in the air return line and cannot return to the compressor quickly. The start-up with liquid caused by refrigerant migration can also cause difficulty in internal oil return, but it usually takes a short time, up to ten minutes.
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