Does the screw-type refrigeration compressor shut down due to an alarm for a high oil filter pressure difference?

Oil is leaking; the refrigeration oil has been carried away by the refrigerant. Our centrifugal chillers here are having the same problem. I’ve collected an article describing and addressing this issue; I hope it helps ； However, our machine’s distributors did not use this method to collect oil; instead, they released it directly, pouring out 5 barrels of oil at once from the evaporator. The evaporator is half full. ~~~~~~~~~~~~~~~~~~~~~~~~~~ During the commissioning of chillers, it is common to encounter oil leakage issues with these units. Most of the units that suffer from this problem use full-liquid evaporators; here, I would like to share some practical experience and insights for discussion. Currently, many units on the market are designed following this approach: the refrigeration oil is mixed with the refrigerant, an oil separator is used to separate the oil from the refrigerant, and then the refrigerant returns to the compressor via a full-liquid evaporator. This model offers excellent cooling performance and is widely used. However, it has a problem during operation: it tends to experience oil leakage. When the temperature of the cooling water is low, the exhaust superheat is not high, which results in incomplete separation of the oil from the refrigerant. This mixture entering the heat exchanger causes low pressure in the unit; in severe cases, it can even lead to blockage of the expansion valve and prevent the unit from starting. The fault symptoms are as follows: 1. No trace of oil can be seen inside the oil separator; at this point, the oil does not accumulate in the condenser but passes through the expansion valve and enters the evaporator. The oil adheres to the copper tubes used for heat exchange in the evaporator, which reduces its evaporation efficiency, resulting in low pressure inside the evaporator. This also leads to a very low superheat of the refrigerant being drawn in by the compressor, or even direct intake of liquid refrigerant. Additionally, the discharge temperature of the compressor is low, and the oil still cannot be separated from the refrigerant. This vicious cycle causes all the oil to accumulate in the evaporator, the compressor generates loud noises due to insufficient oil supply, and in some cases, the unit shuts down due to an oil level alarm in the oil separator. 2. No trace of oil can be seen inside the oil separator; all the oil has gone to the condenser along with the exhaust gas. If the water temperature remains low, all the oil will accumulate in the condenser, causing an oil blockage in the expansion valve. Due to insufficient supply of liquid in the evaporator, the pressure starts to drop, until the system shuts down due to a low-pressure alarm. The above is what is known as oil leakage. The main reason is the low temperature of the chilled water, which results in a low exhaust temperature. The solutions I used to address such problems during startup are as follows: 1. When it is noticed that the oil level in the oil reservoir is dropping, immediately switch the unit to manual control mode in order to limit the compressor’s load, for example by restricting its energy output to 50%. 2. Increase the condensation pressure. 3. Reduce the low-pressure alarm value and low-pressure shutdown value of the unit to acceptable levels, so as to ensure that the unit can remain in operation as much as possible. 4. If the oil level is still very low at this point and the pressure inside the evaporator is also low, it is necessary to consider whether all the oil has moved into the evaporator. Check through the evaporator sight glass to see if there is a large amount of white foam swirling; if so, it indicates that the oil is inside the evaporator, whereas if not, it may be inside the condenser. 5. With these steps followed, after about half an hour, the temperature of the cooling water and the exhaust gas should rise to normal levels. Now, oil collection can begin: A: The oil is inside the evaporator. At this point, it is important to pay close attention to the temperature of the chilled water; the flow rate of this water can be reduced slightly to lower the temperature of the water exiting the evaporator. Afterwards, the flow rate can be increased rapidly, causing the temperature of the water exiting the evaporator to rise sharply. At this stage, the water temperature will be much higher than the saturation temperature of the refrigerant, resulting in intense boiling of the refrigerant. The refrigeration oil will then be drawn into the compressor along with the bubbling refrigerant foam. The discharge temperature should decrease somewhat at this point, but it will still be well above the separation temperature between the oil and the refrigerant, thereby carrying the oil back to the oil separator where they can be separated. After repeating this several times, all the oil will be returned to the oil separator. Pay attention to the time interval between each adjustment of the water volume; it is best to restore the exhaust temperature to its optimal level before each adjustment. B: The oil is in the condenser. At this time, there is no need to pay too much attention to the water temperature; as long as the unit operates properly, there will be no major issues. At this point, the expansion valve should be gradually opened to its maximum setting – the opening process should not be too rapid, in order to prevent excessive liquid supply from damaging the copper tubes inside the evaporator. Wait for a few minutes until the high and low pressures in the unit are balanced; at that time, a large amount of white foam can be seen through the sight glass of the evaporator, indicating that the oil has moved from the condenser into the evaporator. As long as you repeat step A, the oil will be drawn back in quickly

For the one on the first floor, first of all thank you for sharing. I just consulted the manufacturer’s after-sales service: our units do not have an evaporator oil recovery system. To recover the oil from the evaporator, it is necessary to collect all of the Freon first in order to carry out the oil recovery process. To be honest, this is not realistic; our system contains at least around 8T of Freon, and the volume of the Freon storage tank is not large enough, so it’s absolutely impossible to recover it in a short time. Also, I would like to ask what function the oil-removing heat exchanger included in the unit set does? (I’m sorry, I don’t have the structural diagram of the oil-removing heat exchanger.)

What operating conditions? Is the intake temperature over 100 degrees? Then the temperature is set at 48 degrees – how is that achieved? I don’t understand; oil leakage in screw compressors is closely related to operating conditions, as well as the temperature of the circulating water and the condensation temperature. I’m not sure what type of refrigerant you’re using The exhaust temperature is low, oil separation is poor, and the oil contains refrigerant, which causes fluctuations in oil pressure

Freon refrigerant, with a circulating water temperature of around 25 degrees.

There are two reasons: First, the filter element of the oil separator is damaged, or the sealing gasket of the filter element is broken; the solution is to isolate the oil, remove fluorine, and replace the component. II: Low oil temperature while driving: oil leakage due to too rapid loading. Handling method: Under hydraulic pressure, operate at low load and gradually reduce the oil flow.

The evaporator should have an oil return line leading to the machine head, right? It’s impossible not to set it

When the cooling water temperature is low, the exhaust superheat is not high, resulting in incomplete separation of the oil from the refrigerant, and the mixture enters the heat exchanger.

1. The oil temperature is too low, resulting in poor separation. 2. The filter element of the oil separator needs to be replaced. 3. Check whether it is the exhaust pressure or the fuel injection pressure that fluctuates more, as this causes fluctuations in the oil discharge pressure; also check for any faults in the sensors