A compressor is a complex machine running at high speed, to ensure that the compressor crankshaft, bearings, linkage, pistons, and other moving parts of the full lubrication are the basic requirements to maintain the normal operation of the machine. To do this, compressor manufacturers require the use of specified grade lubricants and regular inspection of oil levels and colors.

Lack of oil is one of the compressor faults that can be easily identified, and when the compressor is short of oil, there is little or no oil in the crankcase.

The compressor is a special gas pump, a large amount of refrigerant gas is discharged at the same time to take away a small amount of lubricant (called running oil or running oil). Compressor run oil is unavoidable, but the speed of running oil is different.

About 2-3% of the lubricant in the exhaust of the semi-sealed piston compressor is 0.5-1%of the vortex compressor. For a 6-cylinder compressor with a displacement of 100m3/hrand a crankcase oil storage capacity of 6 liters, 3% of the running oil means about 0.3-0.8 l/min run oil volume, or compressor no return oil running time of ten minutes. If the oil from the compressor does not come back, the compressor will run out of oil.

Compressor returns oil There are two ways: one is oil separator return oil, the other is the return oil return of the return pipe.

Oil separator installed in the compressor exhaust line generally can separate 50-95%of the running oil, oil return effect is good, fast, greatly reduce the amount of oil into the system line, thus effectively extending the operation time without oil.

Pipeline particularly long cold storage refrigeration system, full liquid ice system, and very low-temperature freeze-drying equipment, etc., after the start of ten minutes or even dozens of minutes without oil return or return very little oil is not uncommon, poor design system will appear compressor oil pressure is too low and down the problem. This refrigeration system installed high-efficiency oil separator can greatly extend the compressor no return operation time, so that the compressor safely through the post-power oil-free crisis stage.

Unsolverted lubricants enter the system and flow in the tube with the refrigerant, forming an oil cycle. The lubricant enters the evaporator.

On the one hand, due to low-temperature solubility, part of the lubricant is separated from the refrigerant, on the other hand, the temperature is a low viscosity, the separation of the lubricant is easy to attach to the inner wall of the tube, the flow is difficult. The lower the evaporation temperature, the more difficult it is to return oil. This requires that evaporative line design and return line design and construction must be conducive to oil return, the common practice is to use a drop line design and ensure a large airflow speed.

In practice, oil return problems caused by improper design of evaporators and return lines are not uncommon. For r22 and r404a systems, the return oil of the full-liquid evaporator is relatively difficult and the system return line design must be very careful. For such a system, the use of high-efficiency oil can greatly reduce the amount of oil entering the system lines, effectively extending the return pipe after power-up without oil return time.

When the compressor is higher than the position of the evaporator, a return oil bend on the vertical return trachea is required. The return bend should be as compact as possible to reduce the storage of oil. The spacing between the return oil bends should be appropriate, and some lubricants should be replenished when the number of return bends is relatively large.

The return lines of the load change system must also be careful. When the load decreases, the return speed decreases, and the speed is too low to be conducive to the return of oil. To ensure low-load return oil, a vertical suction pipe can be used double vertical pipe.

The frequent start-up of the compressor is not conducive to oil return. Due to the continuous operation, time is very short compressor stopped, the return pipe is too late to form a stable high-speed airflow, lubricant can only stay in the pipeline. Less oil return than ben oil, the compressor will be short of oil. The shorter the operating time, the longer the pipeline, the more complex the system, the more prominent the oil return problem.

The evaporator temperature increases when defrosted, the viscosity of the lubricant decreases, and it is easy to flow. After the defrost cycle, the refrigerant flows at a high rate, and the trapped lubricant is concentrated back to the compressor. Therefore, the frequency of defrost cycles and the duration of each duration should also be carefully set to avoid large fluctuations in oil levels or even oil shocks. When the refrigerant leaks more, the return gas speed will be reduced, the speed is too low will cause the lubricant to stay in the return line, can not quickly return to the compressor. The fluid start-up caused by refrigerant migration can also cause internal oil return difficulties, but usually for a shorter period of up to ten minutes.