Compressor Not Pressurising Properly? Troubleshooting Guide

Industrial compressed air systems must achieve and maintain defined pressure levels to support safe, continuous production. When a compressor runs without reaching its pressure setpoint, the cause typically lies in air generation failure, pressure loss within the system, or demand exceeding available capacity. Accurate diagnosis depends on separating mechanical performance from system integrity and air consumption.

This guide outlines a structured diagnostic approach used by Search Air, focusing on industrial compressors operating in UK facilities. It addresses common failure modes, technology-specific faults, environmental factors, and regulatory considerations affecting pressure reliability.

Pressure Generation, Retention, and Air Demand

Most pressurisation issues stem from mechanical failure, control errors, or a system demand that has simply outgrown the machine’s capacity. To isolate the fault, operators should categorise the issue into one of three modes:

1. Generation Failure: The compressor pump or motor is not producing the rated volume of air. This is a mechanical fault within the machine itself.
2. Retention Failure: The compressor is producing air, but the system cannot hold it. This is caused by leaks in the distribution pipework or failed internal check valves.
3. Demand Overload: The factory air consumption exceeds the compressor’s Free Air Delivery (FAD). The machine is functional, but the demand exceeds its maximum output.

Isolating the machine is the most effective diagnostic step. Close the service valve to the air receiver. If the compressor reaches its cut-out pressure while isolated, the machine is mechanically sound. The fault exists in the downstream pipework or reflects excessive plant demand.

Control Circuit and Component Failures

In oil-injected rotary screw systems, such as the Atlas Copco GA series, pressure issues usually involve the control circuit rather than a catastrophic failure of the air end. These components work in sequence to manage air intake and internal lubrication.

• Unloader Valve: This valve regulates air intake. If the solenoid fails to actuate, the valve stays closed. The compressor remains in “idling” mode and produces no pressure.
• Minimum Pressure Valve (MPV): The MPV maintains a baseline internal pressure of approximately 4 bar, depending on the model, to ensure oil circulation. If it sticks open, the machine cannot build pressure against an empty downstream network.
• Oil Separator Element: A contaminated separator acts as a physical plug. This prevents air from reaching the discharge outlet and can cause the safety valve to lift due to high internal pressure.

In reciprocating piston compressors, failures are more often linked to mechanical wear. Broken or carbonised valve plates prevent the cylinder from sealing, causing “blow-by” where air moves back and forth within the head rather than into the receiver.

Compressor Not Pressurising Properly? Troubleshooting Guide

UK Environmental Impacts on Pressure

The UK climate presents specific challenges for pressure systems. Moisture and temperature fluctuations directly influence the physical properties of the air and the lubricants within the system.

Moisture and Condensate

UK air is frequently moisture-heavy. Compression forces this water out of the air, creating condensate. If automatic drains fail, liquid water reduces the effective storage volume of the air receiver. Moisture also emulsifies compressor oil. Emulsified oil loses the viscosity required to seal the rotors in a screw compressor, leading to internal pressure leakage and reduced efficiency.

Temperature and Freezing

Condensate trapped in control lines can freeze during the winter months. This ice blocks the pneumatic signals required to open the unloader valve. If the “load” signal is obstructed, the compressor runs indefinitely without producing air. As a practical minimum, maintaining a compressor room temperature above 7°C prevents these ice-related loading failures.

Elektronikon Diagnostic Alerts

Atlas Copco controllers use specific logic to lock out the loading cycle if a sensor detects an unsafe condition or a maintenance requirement. Depending on the firmware revision, the following codes typically indicate why a machine is not building pressure:

If these alerts are active, mechanical checks will not restore pressure until the electronic fault is resolved and the loading cycle is permitted to resume.

Safety and Legal Requirements

The Pressure Systems Safety Regulations 2000 mandate that systems are operated within safe limits. Compressed air must never be used to “feel” for leaks by hand. Even at low pressures, the kinetic energy can cause an air embolism, a condition where air enters the bloodstream, potentially leading to a stroke or heart failure.

Where internal faults or safety devices are involved, intervention by a Competent Person is required. Search Air is an Atlas Copco Premier Distributor providing 24/7 emergency air compressor breakdown repairs across Yorkshire and the East Midlands. Engineers are trained to diagnose Atlas Copco and multi-brand systems to restore production in accordance with UK safety standards.

Diagnostic Guidance Summary

Restoring system pressure requires a logical exclusion of faults:

1. Isolate the compressor to determine if the fault is internal or external.
2. Verify intake conditions to ensure filters are clean and air is available.
3. Audit the control circuit to confirm the machine is receiving a signal to load.
4. Evaluate plant demand to ensure the machine has not been outpaced by new equipment.

If production has expanded, it is necessary to check your air compressor size to ensure it meets current FAD requirements. For persistent pressure drops, a professional compressed air leak detection survey identifies hidden losses in the distribution network.

Search Air provides airCHECK visual inspections and 24/7 emergency repair call-outs for industrial compressed air systems.