Troubleshooting Guide: Compressed Air Pressure Drops – Systematic Leak Detection

1. Problem Description and Scope

This guide is intended for maintenance technicians, reliability engineers and facility managers experiencing unexpected or persistent pressure drops in their industrial compressed air systems. A pressure drop, often characterized by insufficient working pressure at points of use, results in loss of efficiency of pneumatic tools, slowed production cycles and a significant increase in compressor energy consumption. Rigorous diagnosis of this phenomenon is essential to maintain operational efficiency and compliance with industry standards.

Affected equipment includes compressors (screw, centrifugal, piston), buffer tanks, air dryers, filters, main distribution network (rigid pipes), subnetworks (hoses, fittings), pneumatic actuators, valves, pressure regulators and pneumatic tools.

Severity Classification:

• Critical: Imminent or ongoing production shutdown, risks for product quality, major excess energy consumption (increase in compressor electricity consumption of more than 20%).
• Major: Noticeable decrease in productivity, premature wear of downstream equipment, frequent compressor overloads, inability to maintain the minimum pressure required for certain critical processes.
• Minor: Slight drop in efficiency, more frequent activation of compressor charge/discharge cycles, marginally increased energy consumption (less than 10%).

2. Safety Precautions

CRITICAL WARNING: Compressed air systems contain energy under pressure which can cause serious injury or death. It is imperative to follow all safety procedures before any intervention.

• LOCKING/LOCKOUT (LOTO): Before working on any component of the compressed air network or the compressor, ensure that the compressor is electrically isolated (locked out) and that all upstream and downstream isolation valves are closed and padlocked in accordance with standard NF C18-510.
• FULL DEGASSING: Slowly release all residual pressure from the system via the appropriate purges. NEVER open a fitting or component under pressure. Check the total absence of pressure using a reference control pressure gauge (minimum accuracy Class 1.0 according to NF EN 837-1).
• PERSONAL PROTECTIVE EQUIPMENT (PPE): Always wear safety glasses conforming to standard EN 166, hearing protection (helmet or earplugs) if the compressor is operating or degassing, protective gloves EN 388 and safety shoes EN ISO 20345.
• STORED ENERGY: Beware of unexpected movement of cylinders or pneumatic actuators after pressure is released. Secure moving parts.
• HIGH TEMPERATURE: Compressor piping and components may be hot. Allow to cool before handling or use heat protection gloves.

3. Required Diagnostic Tools

The accuracy of the diagnosis relies on the use of adapted and calibrated tools.

4. Initial Assessment Checklist

Before initiating an in-depth diagnosis, a preliminary assessment helps guide the investigation and avoid wasting time.

5. Systematic Diagnostic Flowchart

This process guides the technician through logical steps to isolate the root cause of the pressure drop.

1. Observe the pressure drop:
• If the drop is rapid and immediate when the compressor stops (isolated network): “Significant leaks” or “Defective Check Valve” track.
• If the drop is progressive under load: Track "Excessive Demand", "Undersized Compressor", "Network Obstruction".
• If the pressure does not rise sufficiently when empty: “Compressor Faulty” track.
2. Measure the Differential Pressure:
• Use precision pressure gauges to measure pressure before and after each major component (compressor, dryer, main filter).
• IF a pressure drop > 0.3 bar is observed across a filter: PROBABLE CAUSE: Clogged filter. Go to step 8.1 (Replacing filters).
• IF a pressure drop > 0.5 bar is observed across a dryer: PROBABLE CAUSE: Dryer faulty or saturated. Go to step 8.2 (Dryer maintenance).
3. Isolate the Network and Test the Overall Tightness:
• WARNING: Make sure all points of use are closed and the network is stable.
• Stop the compressor. Leave the system under pressure.
• Monitor the pressure drop on a main pressure gauge for 15-30 minutes.
• IF the pressure drops by more than 0.1 bar in 15 minutes: PROBABLE CAUSE: Significant leaks in the network. Go to step 5.1 (Leak Detection).
• IF pressure is stable: PROBABLE CAUSE: Compressor capacity problem or excessive demand. Proceed to step 5.2 (Demand Analysis).
4. Compressor Diagnosis:
• Check controller settings: cut-off/restart pressure, charge/discharge cycles.
• Measure the current absorbed by the compressor motor with the current clamp. Compare to face value.
• IF the compressor runs continuously and the pressure is low: PROBABLE CAUSE: Excessive demand or undersized compressor. Go to step 5.2 (Demand Analysis).
• IF the compressor has difficulty reaching the target pressure at no load (without demand): PROBABLE CAUSE: Internal compressor problem (worn compression element, defective valve). Request the intervention of a UNITEC-D specialist.
5. Leak Detection (Ultrasonic Method):
• WARNING: The ultrasonic detector may emit loud beeps; use hearing protection.
• With the system under pressure, use the ultrasonic detector. Start with areas with a high concentration of fittings, valves, hoses, and automatic purge points (traps).
• Look for worn o-rings, loose fittings, punctured tubes, continually leaking purges.
• Mark each leak detected (label, marker). Record its intensity in dBμV. A signal > 20 dBμV above the noise floor indicates significant leakage.
• Confirm smaller or hard to locate leaks with a soapy solution.
• Proceed to step 8.3 (Repairing leaks).
6. Air Demand Analysis:
• Install the mass flow meter at the compressor outlet or on the main collector.
• Record air consumption over a significant period of time (min. 24 hours, ideally 7 days) to identify variations in demand, peaks and night/weekend consumption.
• Compare this demand curve to the actual known needs of the equipment.
• IF the measured demand is significantly higher than the actual cumulative demand of the equipment: PROBABLE CAUSE: Abusive use (open blowguns), faulty equipment or undetected leaks. Review operational practices and redo more thorough leak detection.
• IF the measured demand exceeds the capacity of the compressor(s) or is very close: PROBABLE CAUSE: Undersized compressor(s). Go to step 8.4 (Optimizing sizing).

6. Matrix of Failures and Causes

This matrix facilitates the rapid identification of probable causes based on the symptoms observed.

7. Root Cause Analysis for Each Failure

7.1. Compressed Air Leaks

Explanation: Leaks are the most common and costly cause of pressure drops and excess energy consumption. They result from natural wear of seals (NBR, Viton according to ISO 3601), poorly tightened connections, corrosion of metal pipes (NF EN ISO 8573-1 for air quality), mechanical shocks on hoses (ISO 6224) or internal failures of valves or automatic purges. Even a small leak creates a permanent opening in the system, forcing the compressor to work longer and harder to maintain pressure.

Confirmation: The most effective method is ultrasonic detection. A whistle that is inaudible to the human ear becomes a clear sound signal in the detector's headset. The intensity in dBμV (microvolt decibels) makes it possible to quantify the severity of the leak. Typical leak values ​​range from 5-15 dBμV for small leaks up to 80-100 dBμV for major leaks. The thermal camera can also help by revealing cold spots where air is escaping and expanding.

Damage if not resolved: Leaks can represent up to 30-40% of the total electrical consumption of a compressed air system. They lead to premature wear of the compressor (increased charge/discharge cycles), increased maintenance costs and a risk of production shutdown due to lack of pressure on critical tools.

7.2. Undersized or Failing Compressor

Explanation: An undersized compressor cannot provide sufficient airflow to satisfy the maximum site demand. This may be due to an increase in air consumption over time (addition of new machines, production expansions) without the compression capacity having been adjusted. A faulty compressor, for its part, suffers from internal problems such as wear of the compression elements (screws, pistons), clogging of the suction filters, defective intake/exhaust valves or an overloaded electric motor (see NF EN 60034 for rotating electrical machines).

Confirmation: A demand analysis with a mass flow meter reveals whether air consumption exceeds the compressor's rated capacity. Measuring the electrical power absorbed (kW) by the compressor motor and comparing it to the manufacturer's specifications (NF EN 1012-1) makes it possible to diagnose an overload or loss of efficiency. If the compressor has difficulty reaching its set pressure when empty, this confirms an internal problem.

Damage if not resolved: Thermal overload of the motor, frequent tripping, irreversible damage to the compression element, production of poor quality air (humidity, oil), unplanned shutdowns of the compressor and production.

7.3. Obstructions or Bottlenecks in the Distribution Network

Explanation: Excessive pressure losses in the piping network cause a pressure drop between the compressor and the point of use. They can be caused by clogged line filters (differential pressure > 0.3 bar), partially closed or poorly sized valves, insufficient pipe diameters for the required flow (in accordance with hydraulic sizing principles EN 10255), too many or too small radius elbows, or the accumulation of scale/corrosion inside the pipes.

Confirmation: Measuring differential pressure between the inlet and outlet of filters, dryers and piping segments makes it possible to identify areas with high pressure loss. An internal visual inspection of the pipes (by endoscopy if necessary) can reveal accumulations of contaminants. Calculating theoretical pressure losses for the network (based on diameter, length, flow rate and internal roughness) can confirm a sizing problem.

Damage if not resolved: Reduced tool performance, lengthening of work cycles, increased energy consumption of the compressor to compensate for losses, premature deterioration of downstream equipment due to unstable pressure.

7.4. Check Valve (Check Valve) Defective

Explanation: The check valve, or check valve, located between the compressor and the tank, has the role of preventing compressed air from flowing back into the compression element when the compressor stops or goes into discharge mode. If defective (broken spring, worn seat, blocked foreign object), compressed air from the tank will escape in reverse direction to the compressor, causing a rapid drop in system pressure when the compressor is shut down and the compressor starts up under load.

Confirmation: After shutting down and isolating the compressor, listen carefully to the compressor outlet manifold. A hissing sound or a continuous flow of air indicates backflow of air through the check valve. A quick measurement of the pressure drop after stopping the compressor, having isolated the rest of the network, will confirm this internal leak.

Damage if not resolved: Overload and deterioration of the compressor starting motor, rapid and unexplained loss of system pressure, excess energy consumption, risk of compressor shutdown.

8. Step-by-Step Resolution Procedures

8.1. Replacing and Cleaning Filters

1. WARNING: Carry out the full LOTO procedure for the compressor and isolate the network section affected by the filter. Completely degas the pipe segment.
2. Open the filter housing.
3. Remove the used filter element.
4. Clean the inside of the crankcase with a clean, lint-free cloth.
5. Insert a new filter element of the correct specification (filtration size in microns, flow rate rating) according to the manufacturer's recommendations. Check the mounting direction.
6. Replace the filter housing O-rings (ISO 3601) with new ones.
7. Close the housing by tightening to the recommended torque.
8. Gradually repressurize the system and check for leaks with a soapy solution.

8.2. Air Dryer Maintenance

1. WARNING: Perform the full LOTO procedure and degas the dryer.
2. For refrigeration dryers: Clean condensers with dry compressed air. Check refrigerant charge. Check the correct operation of the condensate trap.
3. For adsorption dryers: Check the condition of the desiccant (humidity indicator). If necessary, replace it according to the manufacturer's instructions. Check the correct operation of the switching valves and the regeneration system.
4. Return to service and check the dew point at the dryer outlet. It must comply with specifications (for example, -20°C for instrument air, NF EN ISO 8573-1 Class 3).

8.3. Leak Repair

1. WARNING: Isolate the leaking section via the isolation valves and carry out the LOTO procedure. Completely degas the affected segment.
2. For threaded connections: Disassemble, clean the threads, apply a new sealant (PTFE tape conforming to NF EN 751-3 or anaerobic paste) and retighten to the specified torque (NF E 29-018 for hydraulic/pneumatic connections).
3. For compression fittings: Check the ring and fitting body. Replace if damaged. Tighten.
4. For hoses: Replace any hose showing cracks, deformation or leaks. Make sure the new hose is the correct diameter and a working pressure greater than or equal to the maximum system pressure (ISO 6224).
5. For valves and actuators: If the leak is coming from the body or stem, an overhaul (change of internal seals) or complete replacement is often necessary.
6. After each repair, repressurize the section and retest with the ultrasonic detector or soap solution to confirm the seal.

8.4. Optimization of Compressor Sizing and Performance

1. If demand analysis has revealed chronic undersizing, evaluate the possibility of adding a backup compressor to handle peak loads or replacing the existing compressor with a higher capacity model.
2. Implement a strict preventative maintenance program for the compressor, including regular replacement of air filters, air/oil separators, compressor oils, and inspection of valves and compression element.
3. Optimize compressor controller settings to minimize no-load cycling and start/stop, adjusting setpoint pressures and pressure bands (hysteresis) to match actual demand while maintaining stable pressure.
4. Consider the installation of a centralized compressor management system (Master Controller) if several units are present, for overall energy optimization.

8.5. Fixing Network Obstructions

1. WARNING: Perform the full LOTO procedure for the compressor and degas the entire network or affected segment.
2. Locate sections with high pressure loss by measuring differential pressure.
3. Inspect the valves: make sure they are fully open (ball valves) or in the correct position.
4. If undersized pipes are identified, consider replacing them with pipes of larger diameter to reduce pressure losses (NF EN ISO 65 for steel tubes, EN 10255). Calculate the optimal diameters according to the flow rate and the length (consult the charts for compressed air).
5. If internal corrosion or scale accumulation is suspected, chemical or mechanical cleaning, or even replacement of the most affected sections, may be necessary.

8.6. Check Valve Repair/Replacement

1. WARNING: Perform the full LOTO procedure and degas the compressor and tank upstream and downstream of the valve.
2. Disassemble the defective check valve.
3. Inspect the valve and its seat for wear, corrosion or foreign objects.
4. If possible and economically viable, replace the internal parts (spring, seal, valve). Otherwise, replace the entire valve with a model of equivalent or higher specification.
5. Reassemble the valve, respecting the direction of assembly. Tighten the fittings to the recommended torque.
6. Repressurize the system and test its operation: the compressor should stop smoothly without significant air return to the compression element.

9. Preventive Measures

The application of preventive measures is essential to avoid the recurrence of pressure drop problems and to optimize energy efficiency.

10. Spare Parts and Components

Having the right spare parts is essential for rapid troubleshooting.

For quick access to our complete range of spare parts and industrial components, please consult our e-catalogue: www.unitecd.com/e-catalog/

11. References

• NF E 48-101: Pneumatic equipment – Graphic symbols and diagrams.
• NF EN 837-1: Pressure gauges – Part 1: Bourdon tube pressure gauges – Dimensions, metrology, requirements and testing.
• NF EN ISO 8573-1: Compressed air – Part 1: Contaminants and purity classes.
• EN 10255: Non-alloy steel tubes suitable for welding and threading – Technical delivery conditions.
• ISO 3601: O-rings – Dimensions.
• ISO 6224: Thermoplastic pipes for industrial uses – Thermoplastic pipes for general use – Specifications.
• NF EN 751-3: Sealants for threaded connections in contact with gases of the three families and gas appliances – Part 3: Unsintered PTFE tapes.
• NF C18-510: Operations on electrical installations or in their vicinity – Prevention of electrical risks.
• NF EN 60034: Rotating electrical machines (series of standards).
• NF EN 1012-1: Compressors and vacuum pumps – Safety requirements – Part 1: Compressors.
• UNITEC-D GmbH: Compressor technical manuals and pneumatic network optimization guides.