Do You Know the Distress Signals of Screw Air Compressors?
Various faults are inevitable during long-term operation of screw air compressors, which will trigger alarms. Especially under high-temperature conditions in summer, screw air compressors are prone to frequent malfunctions. What conditions correspond to each air compressor alarm? And what are the differences in emergency and severity levels? Let’s find out!
Level 2 Alarms
Oil Level Alarm: After the compressor starts, operation continues if the oil level is higher than 1/3 (low oil level switch). If the oil level drops below 1/3 and the condition lasts for 20 consecutive seconds, the "Low Oil Level Alarm" will be triggered and the shutdown procedure will be executed.
Oil Pressure Differential Alarm: After the compressor starts, operation continues if the pressure differential of the oil filter is less than 2 bar. Otherwise, the "High Oil Pressure Differential Alarm" will be triggered and the shutdown procedure will be executed.
High-Low Pressure Differential Alarm: When power is supplied to the compressor motor, high-low pressure differential detection starts at the 20th second. Operation continues if the high-low pressure difference is greater than 1.5 bar. If not, the "Insufficient Oil Supply Pressure Alarm" activates; the solenoid valve SV1 de-energizes, the liquid line shut-off valve de-energizes, and the motor cuts off power.
After the compressor starts, operation continues if the high-low pressure difference exceeds 4 bar. If not, the "Insufficient Oil Supply Pressure Alarm" activates and the shutdown procedure is executed.
Internal Over-temperature Alarm: When power is supplied to the compressor PTC control system, operation continues if the motor temperature detected by the built-in PTC thermistor is lower than 110±5°C and the internal discharge port temperature is lower than 90±5°C. Otherwise, the "Internal Temperature Alarm" is triggered, and a signal is sent to prevent the compressor motor contactor from closing.
During compressor operation, operation continues if the motor temperature detected by the built-in PTC thermistor is lower than 130±5°C and the internal discharge port temperature is lower than 110±5°C. Otherwise, the "Internal Temperature Alarm" is triggered and the shutdown procedure is executed.
Level 1 Alarms (Protection Alarms)
High Discharge Temperature Protection: During compressor operation, operation continues if the discharge temperature is lower than the preset alarm temperature of 100°C. If the temperature exceeds 100°C and lasts for 2 consecutive minutes, the "High Discharge Temperature Alarm" is triggered and the shutdown procedure is executed.
High Discharge Pressure Protection: During compressor operation, operation continues if the discharge pressure is lower than the preset alarm pressure of 2.2 MPa (values vary for different systems). Otherwise, the "High Discharge Pressure Alarm" is triggered and the shutdown procedure is executed.
Low Suction Pressure Protection: During compressor operation, operation continues if the suction pressure is higher than the preset alarm pressure of 0.03 MPa (values vary for different systems). If not, a pre-signal for low suction pressure is generated. When this condition lasts for 10 consecutive seconds, the "Low Suction Pressure Alarm" is triggered and the shutdown procedure is executed.
(Judgment logic for "Low Pressure Bypass Abnormality" related to the bypass solenoid valve; "Low Pressure Unloading Abnormality" will be specified in the corresponding control scheme and coordinated with low pressure alarm judgment)
Overload: Excessive power exceeding the set value outputs an abnormal signal, triggering the "Compressor Overload Alarm".
(Not detected separately in PLC projects; monitored by thermal relays together with overcurrent protection)
Phase Sequence: The phase sequence protector outputs an abnormal signal, triggering the "Phase Sequence Abnormality Alarm".
Overcurrent: Excessive current exceeding the set value outputs an abnormal signal, triggering the "Compressor Overcurrent Alarm".
(Not detected separately in PLC projects; monitored by thermal relays together with overload protection)
Special Notes
Alarm Classification
Level 0 Alarm: Interlock shutdown and enter protection status; manual reset via mechanical switch required. (Emergency Alarm)
Level 1 Alarm: Prompt alarm and shutdown as required; fault elimination and manual reset required. (Protection Alarm)
Level 2 Alarm: Prompt alarm and shutdown as required; automatic recovery after fault inspection and elimination. (Resettable Alarm)
Level 3 Alarm: Prompt only without executing any actions; manual alarm clearing required. Equivalent to the former status indication (Abnormality Prompt Alarm)
Temperature Protection
Three stages in sequence: unloading protection, external discharge temperature protection, built-in PTC protection (for discharge gas and motor).
Prerequisite Definitions
Power supplied to compressor PTC control system: The screw compressor has two power supplies: main power supply (380V) and protection power supply (220V). The PTC system is powered by the protection power supply.
Power supplied to compressor motor: The main power supply of the screw compressor is switched on.
After compressor startup: Startup is completed when the screw compressor loads to 50% following the normal startup sequence.
During compressor operation: The screw compressor runs under three load levels: 50%, 75% and 100%.
Level 2 Alarms
Oil Level Alarm: After the compressor starts, operation continues if the oil level is higher than 1/3 (low oil level switch). If the oil level drops below 1/3 and the condition lasts for 20 consecutive seconds, the "Low Oil Level Alarm" will be triggered and the shutdown procedure will be executed.
Oil Pressure Differential Alarm: After the compressor starts, operation continues if the pressure differential of the oil filter is less than 2 bar. Otherwise, the "High Oil Pressure Differential Alarm" will be triggered and the shutdown procedure will be executed.
High-Low Pressure Differential Alarm: When power is supplied to the compressor motor, high-low pressure differential detection starts at the 20th second. Operation continues if the high-low pressure difference is greater than 1.5 bar. If not, the "Insufficient Oil Supply Pressure Alarm" activates; the solenoid valve SV1 de-energizes, the liquid line shut-off valve de-energizes, and the motor cuts off power.
After the compressor starts, operation continues if the high-low pressure difference exceeds 4 bar. If not, the "Insufficient Oil Supply Pressure Alarm" activates and the shutdown procedure is executed.
Internal Over-temperature Alarm: When power is supplied to the compressor PTC control system, operation continues if the motor temperature detected by the built-in PTC thermistor is lower than 110±5°C and the internal discharge port temperature is lower than 90±5°C. Otherwise, the "Internal Temperature Alarm" is triggered, and a signal is sent to prevent the compressor motor contactor from closing.
During compressor operation, operation continues if the motor temperature detected by the built-in PTC thermistor is lower than 130±5°C and the internal discharge port temperature is lower than 110±5°C. Otherwise, the "Internal Temperature Alarm" is triggered and the shutdown procedure is executed.
Level 1 Alarms (Protection Alarms)
High Discharge Temperature Protection: During compressor operation, operation continues if the discharge temperature is lower than the preset alarm temperature of 100°C. If the temperature exceeds 100°C and lasts for 2 consecutive minutes, the "High Discharge Temperature Alarm" is triggered and the shutdown procedure is executed.
High Discharge Pressure Protection: During compressor operation, operation continues if the discharge pressure is lower than the preset alarm pressure of 2.2 MPa (values vary for different systems). Otherwise, the "High Discharge Pressure Alarm" is triggered and the shutdown procedure is executed.
Low Suction Pressure Protection: During compressor operation, operation continues if the suction pressure is higher than the preset alarm pressure of 0.03 MPa (values vary for different systems). If not, a pre-signal for low suction pressure is generated. When this condition lasts for 10 consecutive seconds, the "Low Suction Pressure Alarm" is triggered and the shutdown procedure is executed.
(Judgment logic for "Low Pressure Bypass Abnormality" related to the bypass solenoid valve; "Low Pressure Unloading Abnormality" will be specified in the corresponding control scheme and coordinated with low pressure alarm judgment)
Overload: Excessive power exceeding the set value outputs an abnormal signal, triggering the "Compressor Overload Alarm".
(Not detected separately in PLC projects; monitored by thermal relays together with overcurrent protection)
Phase Sequence: The phase sequence protector outputs an abnormal signal, triggering the "Phase Sequence Abnormality Alarm".
Overcurrent: Excessive current exceeding the set value outputs an abnormal signal, triggering the "Compressor Overcurrent Alarm".
(Not detected separately in PLC projects; monitored by thermal relays together with overload protection)
Special Notes
Alarm Classification
Level 0 Alarm: Interlock shutdown and enter protection status; manual reset via mechanical switch required. (Emergency Alarm)
Level 1 Alarm: Prompt alarm and shutdown as required; fault elimination and manual reset required. (Protection Alarm)
Level 2 Alarm: Prompt alarm and shutdown as required; automatic recovery after fault inspection and elimination. (Resettable Alarm)
Level 3 Alarm: Prompt only without executing any actions; manual alarm clearing required. Equivalent to the former status indication (Abnormality Prompt Alarm)
Temperature Protection
Three stages in sequence: unloading protection, external discharge temperature protection, built-in PTC protection (for discharge gas and motor).
Prerequisite Definitions
Power supplied to compressor PTC control system: The screw compressor has two power supplies: main power supply (380V) and protection power supply (220V). The PTC system is powered by the protection power supply.
Power supplied to compressor motor: The main power supply of the screw compressor is switched on.
After compressor startup: Startup is completed when the screw compressor loads to 50% following the normal startup sequence.
During compressor operation: The screw compressor runs under three load levels: 50%, 75% and 100%.
