If a compressor doesn’t start, it can mess up production schedules and cause unplanned downtime. Usually, this problem isn’t caused by a broken part; it’s caused by safety interlocks or mistakes in the setup.
When modern control systems find dangerous situations, like high pressure or an imbalance in the phase, they stop working. This guide will show you how to safely fix these issues and get your system back up and running.
Is the System Safe to Inspect?
Safety checks are the first step before inspecting any industrial machinery. Industrial air compressors contain stored electrical and pneumatic energy. This includes parts that use high voltage and tanks that hold pressurised air.
The Pressure Systems Safety Regulations 2000 (PSSR) tell you how to use them safely. To stop machines from starting up by accident, it’s important to follow Lockout/Tagout (LOTO) rules.
Key Safety Checks:
- Wait for Discharge: Variable Speed Drive (VSD) compressors use capacitors to store electrical energy. After the power is turned off, these capacitors usually need about 10 minutes to fully discharge.
- Depressurise: Before any service valves are opened, the separator tank should be vented to zero bar. Opening a pressurised system can release oil mist and air with significant force.
- Check Gauges: Checking the pressure gauge ensures the system is depressurised.
A failure to start is often a protective state designed to keep the machine within Safe Operating Limits (SOL). Bypassing these safety features is not recommended.
Why Do Electrical Supply Issues Prevent Startup?
For reliable operation, a stable 400–415V three-phase supply is needed. Changes in voltage or power outages can cause protective shutdowns.
- Blown Fuses: The main distribution board is a good place to start checking for a blown fuse. HRC fuses can sometimes fail due to metal fatigue from repeated thermal cycling.
- Single Phasing: It is important to verify that all three phases are reaching the compressor terminals. The loss of one phase, known as “single phasing,” prevents the electric motor from generating a rotating field. This condition can cause the motor to overheat without turning.
- Loose Connections: Loose terminals in the electrical cabinet can create resistance. This may lead to arcing or intermittent start failures.
- Phase Sequence: Rotary screw compressors often use a K25 Phase Sequence Relay. This device ensures the incoming power creates the correct rotation direction. If two phases are swapped during building maintenance, the relay will stop the start sequence.
- DC Bus Voltage: For VSD units, the DC bus voltage needs to stabilise before the system allows a start. If the mains power is weak, the DC bus might not reach the required charge level.
Regular air compressor service visits can help identify these electrical issues early.
How Does the Control System Block Operation?
The Elektronikon controller manages the safety logic for Atlas Copco machines. It continuously monitors sensors for thermal or pressure anomalies.
Common Control Inhibits:
- Start Limits: Most motors have a limit on the maximum number of starts per hour. Starting a large motor too frequently can cause windings to overheat. If this limit is exceeded, the controller may enter a “Start Inhibit” state.
- Sensor Errors: Thermal sensors, such as PT1000 or NTC types, monitor the temperature of the motor and element. A broken wire or loose connection can simulate a high-temperature reading. The controller interprets this as a malfunction and prevents the machine from running.
- Communication Faults: VSD units rely on a communication cable to talk to the main controller. Vibration can sometimes loosen this connection. A communication error will stop the machine to ensure safety.
You may need to diagnose the problem by checking the physical connections on the drive.
Can Mechanical Resistance Stop the Motor?
Rotary screw compressors are designed to start in an “unloaded” state. Unloaded means the motor turns the rotors without compressing air immediately. This reduces the torque required to spin the heavy components.
Mechanical Failure Points:
- Stuck Unloader Valve: The unloader valve manages the intake process. If the unloader valve sticks in the open position, the motor attempts a “loaded start.” This forces the motor to compress air from the very first rotation. A loaded start significantly increases torque demand and often triggers an overload.
- Low Oil Levels: Low oil levels can also prevent startup on many modern units. Oil level sensors may inhibit operation to protect the air end from damage.
- Minimum Pressure Valve (MPV): The MPV helps maintain internal system pressure for oil circulation. If the MPV fails, the system might not cycle correctly. Sourcing the correct air compressor spare parts is essential for resolving valve failures.
- Internal Pressure: Excessive internal pressure can physically block the motor. The internal tank pressure should blow down after the machine stops. If the tank retains pressure, the motor may struggle to overcome the resistance.
Why Won’t My Piston Compressor Start?
Piston compressors have different operating characteristics and failure modes compared to screw compressors.
- Faulty Start Capacitor: A faulty start capacitor is a common issue on single-phase units. The capacitor provides the extra torque needed to get the motor spinning. If the capacitor fails, the motor may hum loudly but fail to turn. Power should be turned off quickly to avoid damage to the windings.
- Pressure Switch Issues: The pressure switch is another key component to check. A faulty pressure switch might fail to close the circuit when air pressure drops. If the switch contacts are worn or burnt, power cannot reach the motor. You may need to replace the pressure switch to restore automatic operation.
- Check Valve Failure: The tank check valve at the receiver inlet can also cause starting issues. A leaking check valve allows compressed air to backflow into the pump head. This creates excess pressure against the piston. The piston cannot easily push against this head pressure during startup. This often causes the breaker to trip or drive belts to slip.
- Worn Components: A worn piston or ring can reduce the unit’s ability to build pressure. This often leads to rapid cycling, which may eventually trip the thermal overload.
You should also look for air leaks in the pipes that carry the air. Big leaks can make the compressor run too much and get too hot. Professionals who find leaks can help find these problems.
What Environmental Factors Affect Startup?
The UK climate can impact compressor performance, especially in winter.
- Cold Oil: Standard ISO 46 compressor oil tends to thicken in cold temperatures. Thicker oil increases drag on the screw rotors or bearings. This increases the torque required to turn the element. The motor may trip on overload during a cold start attempt. Using oil heaters can keep the oil fluid.
- Frozen Controls: Condensate can freeze in pneumatic control lines. Ice can block the signal to the unloader valve. This prevents the valve from functioning correctly during the start sequence.
- Damp Electronics: High humidity can lead to condensation inside electrical panels. Moisture on circuit boards can cause ghost faults or sensor errors. Damp conditions can also cause auxiliary fuses to blow.
Keeping electrical cabinets clean and dry helps prevent these issues. It is also good practice to inspect air filters for dampness. A dirty air filter that freezes can become a solid block. This restricts the air intake and can starve the compressor.
When is Professional Repair Required?
Some faults require the attention of a certified engineer. Internal components of VSD drives should not be repaired by general maintenance staff. Mechanical seizures in the air end often require a major overhaul.
- Seized Pump: If the motor sounds like it is straining and trips the breaker instantly, the pump may be seized.
- Motor Failures: A motor problem involving internal windings typically requires a specialist replacement.
- Safety Lockouts: If a safety lockout cannot be reset, it is best to call a professional.
Design Air provides a 24/7 compressor repair service for urgent breakdowns. Our engineers have the tools to read deep-level fault codes and diagnose the problem accurately. We can also help verify compliance with PSSR regulations.
If a machine is beyond economical repair, we can advise on replacement air compressors. Prompt professional support helps minimise production losses and ensures safety. Contact us today.
