Several oil separators

Figure 1: Oil separators of air compressors.

During the use of your air compressor, there could be tricky oil separator burning failures. So this article will tell you the causes and solutions as well as some cases.

Oil Separator Burning Failure in Winter

In cold weather, air compressor oils are more viscous, and the oil flow decreases. When the machine stops for a period of time, most lubricating oils in the oil cooler have flowed back to the oil barrel. When it starts again, the lubricating oil becomes more viscous due to the low temperature, and the main engine is in a state of oil shortage for a period of time. The dry friction of the rotors is easy to produce an open flame, which is sprayed into the oil and gas barrel to ignite the oil separator.

Main Engine Lubricating Oil System Defects

Machines with defective oil system design or without temperature control valves may burn oil on the first start after a period of downtime or maintenance. When the machine starts, the main engine needs to pump the air to make the oil enter.

Because there is no temperature control valve in the oil circuit design, it is bound to cause the oil supply time to be longer, leading to the lack of oil and the fire combustion to the oil separator. Some new maintenance workers do not add oil to the air compressor oil filter or the main engine, but directly start the machine after maintenance, resulting in oil separator burning.

Main Engine Lubricating Oil System Failures Leading to Insufficient Oil Supply

The main engine lubricating oil system failure leads to insufficient oil supply, so the main engine can not get lubrication and cooling. Rotors, internal cavity, and end face due to dry friction, which produces sparks due to high-speed rotation. Going through the rear end of the exhaust pipe and entering into the barrel, sparks will ignite the oil separator. The small amounts of lubricating oils in the compression chamber will rub on rotors, the compression chamber, and the end face, which tend to be combustible.

This situation occurs in a very short time, leading to the delay of the temperature sensor. As a result, high-temperature jump protection could not respond in time when the oil core had been burned. If the supply of the oil system fails, the machine runs, and the intake valve is fully open, a large amount of air will be absorbed into the main engine. The lack of oil lubrication and cooling during compression is accompanied by a sharp and harsh dry friction sound during the operation. The sparks due to the dry friction enter into the oil and gas barrel, and the hot air in the role of the fire will rapidly expand, burning the oil separator. Then the safety valve jumps and the machine automatically jumps.

the fuel system of the compressor

Figure 2: The main engine lubricating oil system.

Some customers stated that the compressor with high-temperature protection would not burn out. The principle of high-temperature protection is that the temperature sensor is connected with the PC of the machine. The sensor detects the temperature of the exhaust port of the main engine and monitors the temperature value transmitted by it at any time. When reaching the set temperature, the control circuit will be disconnected and shut down to prevent the machine from running at s high temperature for a long time. And the high-temperature protection system is mainly to protect the machine from overheat caused by general factors, such as insufficient oil in the oil separator, bad cooling effect, temperature control valve failure causing a small channel for the oil entering into the cooler, opened bypass, and oil deterioration.

However, the protection mechanism cannot avoid immediate shutdown due to the lack of oil entering the cooling main and auxiliary rotors in the main engine and internal cavity friction caused by the flame.

If a fire is burning the sensor, will high-temperature protection extinguish the fire? No! The temperature sensor can only transmit the signal to the PC when it is heated slowly (temperature sensing with a delay) so that the computer can disconnect the circuit, the high-temperature protection jumps and the motor is powered off, at this time the main engine can not immediately stop running.

* Troubleshooting

Check whether the structure of the temperature control valve is complete? Is it working properly? Is there any short connection?

Check whether the oil break valve is in good condition. Is the voltage normal?

Is the oil normal? Is the oil system clean?

Air Inlet of the Air Compressor

There are impurities in the air inlet of the air compressor, such as metal particles, papers, fibers, which are inhaled to the main engine. Then the friction of the main and auxiliary rotors produces an open fire entering the oil and gas barrel to ignite the oil separator. This kind of situation mostly occurs after installing a new machine or mainframe maintenance.

Static Electricity Release

Is the machine grounded or is there bad contact? Refer to ground resistor S5 Ohms.

Does the oil separator conduct with the ground wire connected to the machine?

Check whether the oil core asbestos conductive sheet is in good contact with the oil separator (whether there is the contact blockage leading to the bad contact)?

Whether the oil core has an electrostatic conducting system or whether the electrostatic conducting system is normal.

Short Circuit

The open fire caused by the short circuit of the electrical circuit ignited the sound insulation cotton of the machine, burned through the intake pipe, and the fire entered the inside of the air compressor to the oil separator and burned the oil and other accessories, such as the minimum pressure valve, the exhaust pipe and the cooler.

Bad Compressor Oil

Air compressor oil of bad quality is easy to produce carbon deposit or glue that is residual in the various parts of the oil system, leading to the system blocking, the main engine oil shortage caused by dry friction to produce open fire to ignite the oil separator.


To effectively reduce oil core burning failures, combined with previous experience, there are seven preventive measures for reference.

If the compressor has been stopped for a period of time in cold weather or some other reason, the machine will stop immediately after the star triangle conversion is completed. After a few minutes, the machine will start again at several points to make the temperature of the lubricating oil rise and the oil is easy to flow before starting up.

two types of temperature control valve

Figure 3: The temperature control valve.

They should be equipped with the temperature control valve which controls the injection temperature of the main engine by the opening degree of temperature control elements. It can go through the large circulation to cool the lubricating oil to control the exhaust temperature of the main engine when the machine operation reaches a certain temperature.

When the machine is running at a low temperature or starting up, the oil can quickly reach the head through a smaller circulation to avoid the oil shortage of the head for a short time due to the high temperature.

You should replace it with an original temperature control valve as soon as possible.

Regularly check the valve parts of the oil system and make records. Once there are failures, troubleshoot the compressor timely.

When installing the new main engine or maintenance, the air inlet and outlet of the compressor head should be sealed in the whole process by covering it with clean large pieces of cloth or adhesive tape.

When installing the oil separator, you should ensure that conductive copper sheets or conductive nails on the top of the asbestos gasket are in contact directly with the oil separator and keep the touch plane clean. Besides, you should check if the compressor is normally earthed, and the oil and gas bucket is connected with the ground wire of the machine.

The electric enclosure of an air compressor should be manufactured by a normal brand with clean electrical components, such as fiber, foam, and other flammables to prevent a fire.

You should ensure the correct selection of filters and the oil according to the working conditions, timely maintenance, and make records and try to avoid extended use.

Case Studies

Case 1

A 40-cubic compressor has only been used for three days but there was an abnormal smell in the oil separator. After checking it, maintenance workers found that the oil separator core had been burned. A section of pipe at the air outlet of the main engine was tobacco-yellow. By troubleshooting the oil system, they saw that the temperature control valve had been short-circuited.

oil separator burning failure

Figure 4: The oil separator core has been burned.

Case 2

A 100-horsepower permanent-magnet varied-frequency air compressor was burning. The internal head was seriously coking and carbon accumulation. There were friction scratches on rotors, an obvious handle burr on the shaft sleeve of the exhaust end of rotors, and there was an obvious point at the exhaust end of the main rotor that turned blue due to the friction and high temperature. Therefore, it was highly likely that the friction between the rotors and the internal cavity produced an open fire that entered the oil barrel and ignited the filter material of the oil separator, resulting in the oil burning.

the compressor burning failure

Figure 5: A yellow section on the outlet of the head.

Case 3

The minimum pressure valve, oil core, sound insulation cotton, and machine panel were all burnt out. It’s because the air compressor has been running for 10,000 hours without any maintenance.

compressor oil separator burned out

Figure 6: The oil separator is burned to be black.

Related Info

7 Reasons Why an Air Compressor is Overheating - Causes & Solutions

How to Prevent Air Compressor High Oil Consumption

Factors Affecting Service Life of the Air Compressor Oil