Systematic error diagnosis in the event of a pressure drop in compressed air systems: leak detection, needs analysis and network optimization

Problem description & scope

This guide is intended to systematically diagnose and resolve pressure drops in compressed air systems, a critical issue that reduces the efficiency of production facilities and incurs significant energy costs. A pressure drop, defined as a significant reduction in operating pressure below the required value, can manifest itself at various points in the system - from the compressor to the distribution lines to the consumers. All systems that rely on a stable and sufficient supply of compressed air are affected, especially in manufacturing, automation and process technology.

The effects of a pressure drop can be classified as follows:

• Critical: Leads to machine downtime, quality defects in production or safety risks (e.g. in pneumatic controls). Immediate intervention is essential here.
• Major: Significantly reduces the productivity of equipment or tools, increases energy consumption unnecessarily and causes premature wear of components.
• Minor: Leads to moderate efficiency losses and slightly increased operating costs, but these can become significant in the long term.

Typical signs are reduced tool performance, slow machine cycles, frequent compressor starts or visible deviations on pressure gauges.

Safety precautions

WARNING: Working on compressed air systems involves considerable risks. Improper handling can result in serious injury or property damage. Always observe the following safety measures:

• Personal protective equipment (PPE): Always wear safety glasses, hearing protection and safety gloves in accordance with BGR 192/194.
• Lockout/Tagout (LOTO): Before maintenance or repair work, the system must be depressurized and secured against being switched on again (according to DGUV rule 113-001). Close the valves, bleed the system and mark “Do not switch”.
• Stored energy: Compressed air storage (tank) and lines can remain under pressure even after the compressor has been switched off. Bleed the entire system carefully and check the lack of pressure using a pressure gauge.
• Hazardous Conditions: Never work on lines or components that are under pressure. Avoid aiming compressed air at people. Be aware of the ambient temperature and the surfaces of components that may become hot during operation.

Diagnostic tools required

Checklist for initial assessment

Before detailed diagnostic work begins, a comprehensive initial assessment is essential. Collect the following information:

Systematic diagnostic flow plan

This flowchart guides the technician through structured troubleshooting, starting with locating the pressure drop.

1. Symptom: Pressure drop can be detected in the system.
   1. Checking the system pressure at key points:
      • Measurement at the compressor outlet: If the pressure here is already too low (e.g. < 6.5 bar at target pressure 7 bar), the problem is with the compressor or its control.
      • Measurement at the main manifold: If the compressor output is normal, but the main manifold is suffering from pressure (e.g. Delta P > 0.5 bar to the compressor output), this indicates a bottleneck or leaks in the main pipe network.
      • Measurement at the consumer: If the main distributor pressure is normal, but the consumer has a defect (e.g. Delta P > 1.0 bar to the main distributor), the problem lies in the local supply line or in the consumer itself.
   2. If a pressure drop occurs in the entire system:
      1. Leak detection with ultrasonic leak detector:
         • Method: Bring the system to the target pressure, switch off all consumers. Use the ultrasonic leak detector to systematically search all pipes, screw connections, fittings, hoses, steam traps and consumers.
         • Thresholds: An audible hissing sound generated by the detector above 80 dB (typically shown on the display) indicates a leak that requires priority attention. Smaller leaks can be identified with lower noise levels (< 70 dB).
         • Action: Immediately mark and document every identified leak.
      2. Demand analysis with flow meter:
         • Method: Installation of a calibrated flow meter at the compressor outlet or in the main manifold. Long-term measurement (at least 24 hours) to record peak loads and base load consumption.
         • Analysis: Comparison of the measured consumption with the nominal performance of the compressor. An unusually high base load consumption when consumers are switched off indicates massive leaks. Peaks that exceed compressor capacity indicate inadequate design or uncoordinated processes.
         • Action: If basic consumption is too high: Priority is given to fixing the leak. For peak load problems: check process optimization or compressor upgrade.
      3. Compressor performance check:
         • Method: Compressor maintenance log check, air filter condition, oil level (if applicable), control function (control pressure, on/off switch points).
         • Action: Carry out maintenance according to manufacturer's specifications, change filters, check settings.
   3. If pressure drop occurs locally at a consumer or in a sub-area:
      1. Checking the local filters and regulators:
         • Method: Measurement of the differential pressure before and after filters/regulators using a precision pressure gauge.
         • Threshold values: A differential pressure > 0.5 bar across a filter element indicates a blockage. For pressure reducers, the output pressure should be stable and correspond exactly to the setpoint. Fluctuations > 0.2 bar are critical.
         • Action: Replace clogged filter elements. Adjust or replace defective or incorrectly set pressure regulators.
      2. Visual inspection of local pipelines/hoses:
         • Method: Check for kinks, tapers, undersized diameters, corrosion or damage.
         • Action: Replace damaged or undersized lines according to VDI 3474.
      3. Checking the consumer itself:
         • Method: Check whether the consumer (e.g. cylinder, tool) itself has excessive air consumption or has internal leaks. If necessary, isolate the consumer and measure its compressed air requirement separately.
         • Action: Maintenance or replacement of the consumer if a defect is discovered.

Error cause matrix

Root cause analysis for each error

1. Leaks

Explanation: Leaks occur due to material fatigue, corrosion, improper assembly, vibrations or inadequate maintenance on pipe connections, screw connections, hoses, seals, fittings and steam traps. Even the smallest leaks add up to a significant overall loss.

Confirmation: Ultrasonic leak detection is the primary method. In addition, a pressure drop test of the insulated network (pressure maintenance test) can be carried out. A pressure drop of > 0.1 bar per minute when the compressors and consumers are switched off indicates significant leaks. Thermography can show temperature gradients in some leaks (escape of cold air).

Consequences of non-remediation: Continuously high energy consumption as the compressor has to work harder and longer to compensate for the pressure loss. Reduced efficiency of end users, increased wear on the compressor and compressed air preparation due to higher running times and load cycles. Non-conforming products can result if the working pressure is not achieved.

2. Oversized demand / new consumers

Explanation: If the sum of the current air requirements of the connected consumers exceeds the maximum delivery quantity of the compressor, a pressure drop occurs. This can be caused by the commissioning of new systems, inefficient or incorrectly sized tools or uncoordinated processes (starting many large consumers at the same time).

Confirmation: Long-term flow measurement at the compressor outlet or main distributor. The recorded maximum flow (peak load) exceeds the compressor's rated delivery rate. Comparing production planning with flow data can reveal correlations.

Consequences of non-remediation: Chronic lack of pressure, insufficient consumer performance, constant running of the compressor at full load or frequent cycling, which leads to increased energy consumption and premature wear.

3. Clogged filter elements

Explanation: Compressed air filters (pre-filters, fine filters, microfilters) remove particles, oil and water from the compressed air. Over time, these filter elements become clogged, increasing flow resistance and causing a drop in pressure. The maintenance intervals according to the manufacturer's instructions or the monitoring of the differential pressure are critical here.

Confirmation: Measurement of the differential pressure directly above the filter housing using a precision pressure gauge. A differential pressure > 0.5 bar (or above the limit specified by the manufacturer) indicates a blockage. Visual inspection of the filter element for heavy contamination.

Consequences of non-remediation: Reduced operating pressure after the filter, reduced air quality (if the filter effect is impaired), increased energy consumption due to the higher back pressure, increased load on the compressor.

4. Defective/incorrectly set pressure reducer

Explanation: Pressure reducers (pressure regulators) ensure a constant output pressure for certain consumers or system parts. A defect (e.g. jammed valve, worn membrane) or incorrect setting can result in the desired pressure not being achieved or fluctuating significantly.

Confirmation: Measurement of the pressure before and after the pressure reducer. If set correctly, the output pressure should be stable and equal to the setpoint. Deviations > 0.2 bar or an unstable control indicate an error. Leaks on the controller itself can also be checked using an ultrasonic detector.

Consequences of non-remediation: Inconstant working pressure on the consumer, malfunctions of pneumatic components, quality defects in processes, increased wear on the downstream components.

5. Undersized piping/bottlenecks

Explanation: If the diameter of the pipes is too small for the volume of air transported or if there are too many elbows, valves or other flow resistance, this leads to a permanent pressure drop along the pipe. This is often a problem with older systems or inadequate planning for expansions.

Confirmation: Calculation of the pressure loss over the pipe length and diameter using flow diagrams or the Darcy-Weisbach formula. Comparison with the actual pressure drop measured with pressure gauges at the beginning and end of a pipe section. Visual inspection for cross-sections that are too narrow (e.g. in hoses) or corrosion inside steel pipes is also relevant.

Consequences of non-remediation: Permanent pressure loss that cannot be eliminated by eliminating the leak or increasing the capacity of the compressor because the flow is physically obstructed. High energy costs to compensate for the pressure loss. Significant limitations on system performance.

Step-by-step troubleshooting procedures

Procedure 1: Fixing leaks

1. Ensuring safety: Depressurize and secure the affected line section according to the LOTO procedure.
2. Mark leak point: Check marked points during ultrasonic leak detection.
3. Check component: Assess the condition of the seal, screw connection, hose or fitting.
4. Repair/replacement:
   • If seals are damaged: Replace seal according to DIN EN 377 (O-rings) or DIN EN 1514 (flat seals) with new, suitable ones.
   • For loose screw connections: Tighten connections according to the manufacturer's specifications with the recommended torque. Use thread sealant (e.g. PTFE tape or liquid sealant) in accordance with DIN EN 751.
   • If hoses/pipes are defective: Cut out damaged sections and replace them with new, media-resistant and pressure-resistant materials. Establish a connection using compliant plug connections or compression fittings.
   • If the fittings/steam traps are defective: completely replace the component with a new, tested spare part.
5. Verification: After the repair, slowly pressurize the pipe section again. Carry out ultrasonic leak detection again to confirm tightness. Check that the system pressure remains stable.

Method 2: Adjustment in case of excessive demand

1. Needs analysis: Evaluate the results of the flow measurement. Identify which consumers or processes are causing the demand spikes.
2. Process optimization:
   • Avoid simultaneous use of high consumers.
   • Optimize pneumatic cycles to reduce cycle time where possible.
   • Check alternative technologies (e.g. electric drives instead of pneumatic cylinders for high power or long distances).
3. Tool audit: Testing of all compressed air tools for efficiency. Replace old, inefficient tools with modern, energy-efficient models.
4. Compressed air management systems: Implementation of controls that intelligently regulate the compressed air flow and adapt the pressure to requirements (e.g. pressure regulator with fieldbus interface).
5. Verification: Flow measurement again after the measures. Checking compressor running times and system pressure for stability. The aim is to reduce compressor switching cycles and achieve stable pressure with minimal energy use.

Procedure 3: Clear filter blockages and regulator defects

1. Ensuring safety: Depressurize and secure the affected filter/regulator station (LOTO).
2. Replace filter elements:
   • Open the housing, remove the used filter element.
   • Clean sealing surfaces.
   • Insert a new filter element of the correct type (e.g. 1 µm fine filter, 0.01 µm microfilter) according to ISO 8573-1.
   • Replace O-rings and close housing.
3. Check/replace pressure reducer:
   • If adjustment is possible: Loosen the adjusting screw, set the pressure to the target value (e.g. 6 bar for a specific tool).
   • If the regulator is defective (unstable pressure, leakage, setting error): Replace the entire regulator with a new, suitable model.
4. Verification: Re-pressurize the system. Differential pressure measurement via the new filter. Check outlet pressure at regulator. Both values ​​must meet specifications.

Preventive measures

Spare parts & components

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References

• DIN EN 13306: Maintenance – Terminology
• ISO 8573-1: Compressed air – Part 1: Impurities and purity classes
• VDI 3474: Compressed air systems – dimensioning and design
• VDI 3489: Compressed air systems – planning and operation
• DGUV Rule 113-001: Working in containers, silos and narrow spaces
• BGR 192/194: Use of eye and face protection/hearing protection
• DIN EN 751: Sealant for metal threaded connections in contact with gases of the 1st, 2nd and 3rd families and hot water