Shallow oil return method of parallel refrigeration compressors
Compressor oil return is one of the key problems in piping design, and it is also a troublesome problem that must be solved; the solubility of refrigerant and lubricating oil should be miscible, slightly soluble, and miscible at high pressure and separate at low pressure. ; The problem of oil return often occurs in the exhaust pipe and return pipe. Today, the analysis is the oil return problem of parallel compressors
The oil return of parallel compressors is mainly achieved through the following three methods:
Oil-gas balance method: Oil-gas balance method, also known as gravity oil equalization method or pressure self-balance method; it is mainly realized through oil balance pipe and gas balance pipe.
The compressor oil tanks are connected by a pipe, which is called an oil balance pipe. The balance pipe should be lower than the lowest oil level line in the oil sight glass. Due to the connection of the oil balance pipe, the oil level between the compressors can be balanced to avoid excessive discharge of oil, resulting in a lack of oil in the compressor.
The upper and upper parts of the compressor oil tank are connected by a pipe, which is called a gas balance pipe. The balance pipe can promote the pressure balance between the oil tanks, and the oil level can be the same.
The installation height of the compressors of parallel units should be consistent. If the size of the compressor is not the same, the height of the lowest oil level line on the compressor oil mirror should be consistent.
Oil level control method: The oil level control method refers to the use of mechanical control to make the compressor oil return evenly to the parallel compressors. The following components can be used to achieve oil level control:
1. The oily refrigerant gas from the oil separator is discharged from the compressor exhaust pipe. After entering the large space oil separator, the flow rate slows down and is resisted by the filter. The direction changes, so that the lubricating oil and the refrigerant gas are separated . The refrigerant gas is discharged from the upper air outlet pipe, the lubricating oil falls to the lower part, and the oil stored in the lower part gradually increases, the oil level rises, and the float valve rises accordingly. A
2. Float valve type oil level controller The oil inlet of the float valve type oil level controller is connected with the oil pipeline of the oil discharge port of the reservoir, and the oil level controller is installed at the position of the compressor sight glass.
(1) When the oil level of the lubricant in the compressor oil tank drops, the oil level controller floats down. When the oil level drops to a certain position (higher than the lowest oil level line of the sight glass), the oil inlet opens to lubricate Oil enters the oil controller and the compressor oil tank, the oil level rises, and the float ball floats up.
(2) When the oil level rises to a certain height (below the highest oil level line of the sight glass, the oil inlet is closed and the oil is stopped, so that the compressor oil tank can ensure that there is a proper amount of lubricating oil for the compressor. )
For parallel units with more than three compressors and a relatively large system, the oil level control method is usually used.
Electronic oil level controller: Different from the float valve oil level controller, a solenoid valve is connected to the oil inlet, and the electronic oil level controller has 4 control points:
(1) When the oil level drops to the lower limit control point (higher than the lowest oil level line of the sight glass), the solenoid valve opens, and the lubricating oil enters the electronic electronic oil level controller and the compressor oil tank, and the oil level rises; When the upper limit control point is lower than the highest line of the sight glass, the solenoid valve is closed and the oil supply is stopped.
(2) The oil level drops to the lower limit control point, and the solenoid valve opens, but because the system returns poorly, the oil reservoir is dry and there is no oil available, or the solenoid valve circuit fails, the solenoid valve cannot be opened, and the oil level continues to drop , So the compressor will be in danger of being damaged.
(3) When the oil level drops to the lower limit protection stop point, it will stop and give an alarm to ensure that the compressor is not damaged. If the oil level rises to the upper limit control point and the solenoid valve is not closed, the oil level rises to the upper limit protection stop point, it will also stop and alarm.
Cross oil return: This method is mainly used in multi-line systems. The compressor exhaust enters the oil separation reservoir, the high-pressure refrigerant gas is discharged from the upper part into the condenser, and the lubricating oil falls to the bottom.
When the oil level in the compressor oil tank drops to a lower position, the solenoid valve on the electronic oil level controller will let the oil in the oil separation reservoir enter the electronic oil level controller and the compressor oil tank. When a certain amount is reached, the solenoid valve of the electronic oil level controller is closed to control the compressor oil tank to maintain the normal oil level controller. When the solenoid valve on the oil level controller is opened, the oil flow rate is relatively fast, which will impact the compressor oil tank to produce bubbles. However, this process takes a short time and will not cause any harm.
