Suggestions for troubleshooting of compressor with liquid start First, let's define what is called liquid start. When the refrigeration unit is stopped, there is refrigerant liquid in the compressor casing. The next time the compressor starts, the refrigerant liquid will damage the lubrication of the compressor. Starting the compressor with refrigerant liquid Called to start with liquid.
Then let's take a look at the process of starting the liquid to destroy the compressor. When refrigerant liquid appears in the compressor casing, the liquid tends to stay at the bottom of the compressor and is mixed with the lubricating oil. The lubricating oil and the refrigerant are generally soluble in each other. The solubility and temperature, additives and other conditions are related. Lubrication After the oil and refrigerant are mixed, the characteristics of the lubricating oil will change. The most obvious is that the dynamic viscosity will decrease, which will directly affect the lubrication effect. When the compressor is started again, the motor of the scroll compressor is generally It is directly driven by a three-phase power supply. In most cases, a soft starter will not be installed. In this way, the pressure in the compressor casing drops sharply in an instant, and it is below the saturation pressure of the refrigerant at the current temperature, which will cause The refrigerant liquid in the lubricating oil evaporates rapidly, boiling occurs, and a large amount of foam is generated. When viewed from the oil sight glass of the compressor, as shown in Figure 1 below. Fig. 1 The sight glass of the compressor oil sump when the unit starts with liquid The operating channel of the lubricating oil in the compressor is shown in the following figure. There are generally four parts inside the compressor that need oil lubrication, the lower bearing, the main bearing, the upper bearing and the scroll. The three bearings are matched with the rotating crankshaft to ensure coaxiality, while relative displacement occurs, friction occurs, and oil lubrication is required. The lower bearing is very close to the oil sump, and even the lower bearing of some compressors is designed to be immersed in the oil sump (such as the Danfoss Pfima H and M series compressors), so in general, the lower bearing is the easiest to get Oil parts, do not need to worry about lubrication problems; The oil of the main bearing and the upper bearing is thrown up by the centrifugal force generated by the eccentric hole inside the crankshaft when the crankshaft is running. If a large amount of foam is generated, the foam will block the eccentric hole of the lubricating oil. The oil film is cleaned, and the friction surface is rubbed without sufficient lubrication conditions, which will lead to wear, and it will seriously cause the cylinder to hold the shaft. The most affected by liquid start is the uppermost part of the shaft and the dynamic bearing, because this part is the highest position. It is the most difficult to get lubricating oil, so it will be worn first and cause the compressor to break down.
Figure 2 Air-conditioning scroll compressor sectional view Let's analyze the reasons for the start of carrying liquid. In a normally operating system, there should be no refrigerant liquid in the compressor, but immediately after shutdown, the compressor housing is the lowest pressure point of the entire system, the high pressure side is still high pressure, the system pressure needs to be balanced, and a lot of refrigeration The refrigerant liquid will continue to flow under the effect of the pressure difference. After the evaporator of the system also stops working, no heat is input, and the refrigerant will migrate to the compressor casing in the form of liquid. On the other hand, after shutdown, the refrigerant in the unit must be in a state of gas-liquid mixing, and the liquid will migrate to a lower position. In a closed environment, the liquid is also likely to gather in a place with a low temperature. The location of the temperature is often not high, and the location is also low, which also increases the possibility of liquid refrigerant accumulation. Let's take another look at the measures to prevent the start of liquid-carrying caused by the migration of refrigerant. There are three suggestions: 1. Install the liquid pipe solenoid valve. After the unit is shut down, close the solenoid valve at the same time to trap most of the refrigerant liquid on the high pressure side, which greatly reduces the possibility of starting with liquid. 2. Install the electric heating belt of the compressor. After the compressor is stopped, the electric heating belt is powered on to heat the oil sump, maintain the heat input, maintain the high temperature of the oil sump, evaporate the refrigerant liquid in the oil sump, and avoid the next time. The effect of starting liquid foam. 3. The air return pipeline is designed with an inverted U-shaped bend to prevent the liquid in the evaporator from migrating to the compressor due to the self-weight due to the height difference between the evaporator and the compressor after the shutdown. The evaporator advances in the next start Operation, to evaporate liquid into gas, can ensure safety. 4. Install the gas-liquid separator.
