Deep analysis of oil imbalance in parallel units of cold storage | Rectification plan for uneven oil return, oil leakage due to lack of oil, and pipeline
The imbalance of oil return in parallel units is the first major problem in multi head systems. The oil levels in the crankcases of each head are inconsistent, with some heads being full of oil and others continuously lacking oil. The bearings of the heads that are short of oil are prone to wear and lock up.
The root causes are concentrated in four points: insufficient flow rate of the return gas main, no height difference in the return oil branch pipe, unreasonable start stop rotation logic of the machine head, and small diameter of the shared oil distribution return oil pipeline.
The Xitelide parallel unit is equipped with a header oil separator and a balance oil pipe as standard. The balance oil pipe is installed at the 1/2 oil level position of the crankcase to balance the static oil level of each machine head.
Under low load, only a few machine heads are turned on, resulting in a decrease in the flow rate of the return air main. Oil cannot be brought back to the main engine and accumulates in the evaporator and return air pipe. When the other machine heads are started, a large amount of oil is returned at once, causing oil hammer.
The oil return branch pipe should take oil from the bottom of the return pipe, and tilting the branch pipe upwards is a typical mistake. The frozen oil accumulates in the elbow and cannot flow back to the crankcase; It is recommended to install a sight glass on the return oil branch pipe for easy inspection.
Many engineering companies only focus on refrigerant pipelines and ignore balance oil pipes. The valve of the balance oil pipe is closed, the pipe diameter is too small, and the automatic oil level balancing function fails, resulting in oil level differentiation after a period of operation.
It is not recommended to operate a single machine head at low load for a long time in parallel units. The controller logic should limit the independent operation of the single machine head for a long time, rotate other machine heads at regular intervals, and drive the pipeline to return oil.
The large-scale cold chain parallel project in foreign trade requires separate calculation of return air flow rate and layout of return oil branch pipes during the drawing stage. It is difficult to rectify the pipelines on overseas sites, and the labor cost is extremely high.
A simple method to determine oil return imbalance is to run continuously for 4 hours, check the oil sight glass of each machine head, and if the oil level difference exceeds 1/2 of the window, it is an oil return imbalance, and the pipeline and control logic need to be adjusted.
Do not blindly refuel when an oil shortage alarm occurs. Blindly refueling will only cause other machine heads to have high oil levels, resulting in oil hammer. Prioritize checking the pipeline, return oil flow rate, and rotation logic.
Implant 10 popular search keywords: cold storage parallel unit oil return, multi head compressor, compressor oil leakage, compressor oil hammer, semi closed piston compressor, screw refrigeration compressor, oil separator, compression condensing unit, cold storage engineering company, refrigeration maintenance company
FAQ
1. Visual judgment criteria for oil return imbalance in parallel units? The oil level difference between each machine head exceeds 1/2 of the window.
Where is the installation location of the balance oil pipe? 1/2 oil level height of crankcase.
3. Is there a risk of oil return during low load single head operation? Insufficient flow rate in the return pipe causes frozen oil to accumulate in the pipeline.
What are the requirements for the oil intake position of the oil return branch pipe? Take oil from the bottom of the return pipe.
5. Is it possible to directly replenish oil when there is an oil shortage alarm? Not recommended, it will exacerbate the high oil level in other machine heads.
What is the recommended flow rate range for the return air main of parallel units? 8–12m/s。
What is the function of controller rotation start stop? Drive the pipeline to return oil and avoid long-term single head operation.
