How is the air leakage rate of an air compressor pipeline calculated?

Basic Principles for Calculating Air Leakage Rates

The air‑compressor pipeline leakage rate typically refers to the volume of gas that escapes from the compressed‑air system per unit time. For calculations, it is recommended to treat the piping, air receivers, and associated branch lines as a closed volume; after ceasing air consumption or isolating the point of use, observe the rate at which pressure declines, then convert this data into a leakage rate based on the system’s total volume.

Common Calculation Methods

• Pressure Drop Method:Leakage rate is estimated using the system volume and the pressure drop, making it suitable for rapid on-site assessment.
• Volumetric method:Given the known volume of the container, the rate of free-air leakage per unit time is determined by analyzing changes in pressure differential.
• Flow meter method:Under conditions of air compressor make-up air or no-load operation, the flow rate required to maintain pressure is measured using a flow meter and used as a leakage reference.

Pressure Drop Method Estimation Formula

If there is no significant gas consumption during the test, you can use the following approach to estimate:

• First, determine the total volume of the system to be tested. V, including gas storage tanks, main pipelines, branch pipelines, and associated buffer volumes.
• Record the initial pressure P1 and the final pressure P2, and note the time t required for the pressure drop.
• Converted to free-air volume: the leakage rate is approximately equal to the system volume multiplied by the pressure differential, divided by the time and atmospheric pressure.

Simplified expression:Q≈ V ×(P1-P2)÷t÷P0Here, Q can be understood as the leakage rate converted to atmospheric conditions, and P0 represents the local atmospheric pressure. It is recommended to use absolute pressure consistently; if gauge pressure is used, only a rough comparison at the same nominal diameter is permissible.

On-site testing procedures

• As far as possible, shut down gas‑using equipment or isolate the pipeline under test from the production side.
• Pressurize the system to its normal operating pressure range, and start timing once the pressure has stabilized.
• Record the pressure drop over a specified period of time, and simultaneously log the corresponding timestamps.
• Repeat the test at least twice to eliminate interference from instrument fluctuations and internal valve leakage.
• Assess the severity of the leak based on the rate of pressure drop, then use acoustic inspection, soapy water, or ultrasonic testing to pinpoint the leak’s location.

Factors Affecting Calculation Accuracy

• Inaccurate estimation of the system volume will directly affect the leakage rate results.
• Mixed use of pressure units, such as gauge pressure and absolute pressure, bar, MPa Mixing them will lead to bias.
• During testing, concealed gas consumption, drainage valve discharge, or internal valve leakage were observed.
• Temperature variations can cause pressure fluctuations; therefore, avoid making assessments during periods of rapid temperature changes.
• Insufficient accuracy of pressure gauges or sensors can cause minor leaks to be either amplified or masked.

How to determine whether processing is required

If the pressure drop rate is significantly faster than historical normal values, or if it continues to decline during the shutdown‑pressure‑holding phase, this typically indicates a substantial leak. Connections, flanges, quick‑connect fittings, hoses, drain valves, and aging pipe sections should be inspected first. Leaks not only increase the air compressor’s loading time but can also cause pressure fluctuations, compromising the stable operation of pneumatic equipment.