BIZOMAT MAKEOS · Pneumatics
Compressed-Air Leak Audit (Leak Flow, Power, Cost and Repair Payback)
How much air and money are these compressed-air leaks wasting, what share of the compressor do they use, and how quickly do repairs pay back?
Audit of compressed-air leaks grouped by equivalent hole size: choked flow through each hole as free air (as the air leak cost tool), the total leak flow, its share of compressor capacity, the compressor power and yearly energy cost from your specific power, and the payback of repairing the leaks at your repair cost per leak.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Leaks by size | ||
| Leaks of size 1 | Number of leaks in the smallest group. | |
| Size 1 equivalent hole | mm | Equivalent orifice diameter for that group (from an ultrasonic survey estimate). |
| Leaks of size 2 | Leaks in the middle group. | |
| Size 2 equivalent hole | mm | Equivalent orifice for the middle group. |
| Leaks of size 3 | Leaks in the largest group. | |
| Size 3 equivalent hole | mm | Equivalent orifice for the largest group. |
| System | ||
| Line pressure | bar | Gauge pressure in the line at the leaks. |
| Discharge coefficient | Discharge coefficient of a leak (about 0.6–0.65 for sharp holes). | |
| Air temperature | °C | Air temperature in the line. |
| Compressor specific power | kW per m³/min | Compressor input power per m³/min of free air delivered (from the compressor data sheet). |
| Compressor capacity | m³/min | Air delivered by the running compressors, as free air. |
| Pressurised hours per year | h | Hours per year the system stays pressurised (leaks run even when production stops). |
| Electricity price | $/kWh | Price of electricity. |
| Repair cost per leak | $ | Average cost to repair one leak. |
| Largest leakage share accepted | % | Leakage share of capacity you set as acceptable (well-run systems aim below 10%). |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
Leaks by size
What this means: Leaks of size 1
- What it is
- The number of leaks found in the smallest size group of the survey.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 100000. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Zero leaves this group out.
What this means: Size 1 equivalent hole
- What it is
- The diameter of a sharp-edged round hole that would leak as much as each leak in the smallest group, estimated from the survey.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.1 mm to 50 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Flow per leak rises with the square of this diameter, so size estimates matter.
What this means: Leaks of size 2
- What it is
- The number of leaks found in the middle size group of the survey.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 100000. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Zero leaves this group out.
What this means: Size 2 equivalent hole
- What it is
- The equivalent sharp-edged hole diameter for each leak in the middle group, estimated from the survey.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.1 mm to 50 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Flow per leak rises with the square of this diameter.
What this means: Leaks of size 3
- What it is
- The number of leaks found in the largest size group of the survey.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 100000. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Zero leaves this group out.
What this means: Size 3 equivalent hole
- What it is
- The equivalent sharp-edged hole diameter for each leak in the largest group, estimated from the survey.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.1 mm to 50 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Flow per leak rises with the square of this diameter.
System
What this means: Line pressure
- What it is
- The pressure in the air line at the leaks while the system is pressurised.
- Units and format
- Enter a number in bar: bar (1 bar = 100 kPa). The form accepts 0.000001 bar to 50 bar. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 7 bar as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Leak flow rises in proportion to the absolute line pressure.
- Get it right
- Gauge pressure; the tool adds atmospheric pressure itself.
What this means: Discharge coefficient
- What it is
- The ratio of actual to ideal flow through a leak opening, allowing for the jet contracting as it leaves a sharp edge.
- Units and format
- Enter a plain number with no unit. The form accepts 0.3 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.65 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Leak flow, power and cost rise in direct proportion.
What this means: Air temperature
- What it is
- The temperature of the compressed air in the line at the leaks.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -20 °C to 80 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Compressor specific power
- What it is
- The electrical input power the compressors draw for each cubic metre per minute of free air they deliver, from their data sheet or a system test.
- Units and format
- Enter a number in kW per m³/min: kW per m³/min. The form accepts 0.000001 kW per m³/min to 30 kW per m³/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6.5 kW per m³/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Wasted power and cost rise in direct proportion.
What this means: Compressor capacity
- What it is
- The free air delivery of the compressors that are running, used to express leakage as a share of supply.
- Units and format
- Enter a number in m³/min: cubic metres per minute. The form accepts 0.000001 m³/min to 100000 m³/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 m³/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Pressurised hours per year
- What it is
- The hours per year the network stays under pressure, including nights and weekends if it is not shut off.
- Units and format
- Enter a number in h: hours. The form accepts 0.000001 h to 8784 h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6000 h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Yearly energy and cost rise in direct proportion.
What this means: Electricity price
- What it is
- The price you pay per kilowatt-hour of electricity, including network and demand charges where they apply.
- Units and format
- Enter a number in $/kWh: money per kilowatt-hour. The form accepts $0/kWh to $10/kWh. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $0.25/kWh as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Repair cost per leak
- What it is
- The average cost to find and fix one leak, including labour and parts.
- Units and format
- Enter a number in $: an amount of money; use one currency for every money input. The form accepts $0 to $100000. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $50 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Largest leakage share accepted
- What it is
- The leakage, as a share of compressor capacity, that you set as acceptable for this system.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Method and formulas
- Choked flow per hole ṁ = C_d A p₀ √(k ÷ R T₀) [2 ÷ (k + 1)]^((k+1)/(2(k−1))), as free air at 1.204 kg/m³ (as the air leak cost tool).
- Power = free-air flow (m³/min) × specific power; cost = power × hours × price.
- Repair payback = leaks × repair cost ÷ yearly cost.
- Example: the leaks waste 65.211 L/s (7.8254% of capacity), 25.432 kW and 38,149 a year; repairs pay back in 7.1759 days.
Limitations
- Equivalent-hole estimates from surveys are rough; a drawdown or no-load test measures total leakage directly.
- Assumes the compressors unload efficiently; poor control makes leaks cost more.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Turn a leak survey into a cost and a repair budget
- Show management what leaks cost
- Check leakage against a target share of capacity
Who it is for
- Maintenance engineers
- Energy managers
- Plant engineers
What you get
- Leak flow by group and in total
- Share of compressor capacity, power and yearly cost
- Repair cost and payback
Interpreting the result
- A few large leaks usually waste more than many small ones: fix the largest first.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3032–3041. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Set the pressure and stop the waste
In Compressed Air Plant by the Numbers
What it covers: Price each 100 kPa of CA-1's pressure, see how leaks and open blow-offs grow with it, find the pressure lost before the air leaves the room, and fix a low-pressure complaint at its cause.
Learning pathway
Find what compressed-air leaks cost
Learn how pressure setting and leaks waste compressor energy, then audit the leaks in your own system.
1 Learn
Read Set the pressure and stop the waste in Compressed Air Plant by the Numbers.
Price each 100 kPa of CA-1's pressure, see how leaks and open blow-offs grow with it, find the pressure lost before the air leaves the room, and fix a low-pressure complaint at its cause.
2 Apply
Open Compressed-Air Leak Audit (Leak Flow, Power, Cost and Repair Payback) and enter your own figures.
How much air and money are these compressed-air leaks wasting, what share of the compressor do they use, and how quickly do repairs pay back?
3 Verify
Read the tool’s feasibility and verification checks under the result, and test your answer against its stated limitations:
- Equivalent-hole estimates from surveys are rough; a drawdown or no-load test measures total leakage directly.
- Assumes the compressors unload efficiently; poor control makes leaks cost more.
- Example values are illustrations. Replace them with values for your actual task.
4 Improve
Download the decision report or copy the link with your inputs to keep a record, then change one assumption at a time and compare.
Next reading: Assess the system, then choose equipment in Compressed Air Plant by the Numbers.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Compressed-Air Leak Audit (Leak Flow, Power, Cost and Repair Payback) calculator