Why leaks matter more than they look
Compressed air is one of the most expensive utilities in a factory, because most of the electrical energy put into a compressor ends up as heat rather than useful work. A leak wastes all of that energy continuously, including during lunch breaks, night shifts and weekends whenever the system is pressurised. Leaks also have indirect costs: they lower system pressure, so operators raise the compressor set point, and every extra bar costs about 7% more power. They make compressors run more hours, bring service intervals forward and can force a plant to run an extra compressor it does not really need.
Leaks are rarely one dramatic hole. They are hundreds of small hisses at couplings, hoses, push-fit connectors, regulators, filter bowls, cylinders, valve packings, drains and tools. Some leak all the time; others appear only when a machine is pressurised or cycling. That is why leak management must be a programme, not a single walk-round.
Detection and quantification are different jobs
A good programme separates two questions: where are the leaks, and how much air is the system losing in total?
| Method | What it tells you | Strengths | Limits |
|---|---|---|---|
| Listening and soap solution | Location of large or accessible leaks | No equipment; good for confirming a leak point | Misses small leaks and anything in a noisy plant |
| Ultrasonic leak detector | Location of leaks, even in noisy areas | Fast, finds small leaks, works while production runs | Signal level is not a reliable flow measurement on its own |
| Acoustic imaging camera | Visual location of leaks, often from a distance | Quick on overhead lines and large areas | Flow estimates are method-dependent and approximate |
| Load–unload test (non-production) | Total air lost with no production demand | Simple on load/unload compressors with known capacity | Needs a quiet period; less suited to VSD machines |
| Pressure-decay test | Total air lost from a known volume | Works with any compressor type | Needs a reasonable estimate of system volume |
| Flow meter on the main header | Actual flow at zero production, and real-time demand | Most direct, ideal for verification | Requires a meter installed correctly |
Ultrasonic surveys tell you where to work. Total-loss measurements tell you how big the problem is and, after repairs, whether you have solved it.
How to measure total leakage
Two standard methods suit most Indian plants.
Load–unload method
- Choose a period with no production demand, such as a weekend or shutdown, with the system pressurised and all air users stopped.
- Run a load–unload compressor and record several load times and unload times.
- Leakage is approximately the compressor’s actual delivery multiplied by the load time divided by the total cycle time (load plus unload).
- Use the compressor’s measured or rated free air delivery, and note that worn machines may deliver less than their rating.
Pressure-decay method
- Estimate the system volume: receivers plus the internal volume of the main pipework.
- Pressurise the system to normal working pressure, stop the compressors and isolate them.
- Record the time taken for the pressure to fall between two values, for example from working pressure to a lower value well above zero.
- Leakage in free air is approximately the volume multiplied by the pressure drop (in bar) divided by atmospheric pressure (about 1 bar) and by the time taken.
Both methods give a figure at one pressure on one day. We always record the pressure, the plant state and the method, so that the next test is comparable. If a power and flow logging exercise is running, the night-time and weekend flow trend is an even better picture of leakage.
Running a leak survey that leads to repairs
Surveys fail when they produce a report and no repairs. The structure that works:
- Agree the boundary – which buildings, lines and machines are in scope, and who owns repairs.
- Survey systematically – compressor room, main headers, drops, machines and point-of-use equipment, area by area.
- Tag every leak – a numbered tag on site and a matching entry in a register with location, component, photo, estimated size category and the repair needed.
- Prioritise – large leaks first, then easy repairs, then leaks needing a shutdown or a part.
- Repair – many leaks are fixed on the spot by tightening or re-taping; others need seals, hoses, couplings or valve parts.
- Verify – re-check repaired points and repeat the total-loss test under the same conditions.
- Re-survey – on a regular cycle, because new leaks appear as hoses age and fittings are disturbed.
A leak repair register is the backbone of this process, and our leak repair persistence dashboard shows whether repairs are holding over time.
Where leaks are usually found
| Location | Typical cause | Usual repair |
|---|---|---|
| Quick couplings and hose ends | Worn seals, damaged plugs, hoses dragged on floors | Replace coupling or seal; fit proper hose reels |
| Threaded joints | Vibration, poor sealing, disturbed during maintenance | Remake joint with correct sealant |
| Push-fit connectors and plastic tubing | Tube not cut square, aged tubing, heat damage | Recut and reinsert or replace tubing |
| Filter, regulator and lubricator units | Cracked bowls, worn seals, failed auto drains | Replace bowl seals or drain; check for stuck-open drains |
| Condensate drains | Stuck open, timers set too long, manual valves cracked open | Service or replace with level-sensing drain |
| Cylinders and valves on machines | Worn rod seals, valve spools, exhaust leaking through | Machine maintenance by the user department |
| Open blowing and abandoned lines | Air used for cleaning or cooling; old lines still live | Isolate dead legs; use engineered nozzles or alternatives |
Strictly, open blowing and misuse are not leaks, but they belong to the same artificial-demand problem and should be reviewed during the survey.
Reducing leakage through pressure
Leakage flow rises with pressure. The same hole leaks more air at 8 bar (116 psig) than at 6 bar (87 psig). Once major leaks are repaired, the plant can often lower its generation pressure, which reduces both leakage and compressor power. This is the logic behind system pressure optimisation. Some plants also isolate areas that are not working during weekends or night shifts with valves, so idle sections are not held at full pressure.
Building a programme that lasts
- Make leak reporting easy: tags available on the shop floor and a simple way to log them.
- Give repairs an owner and a target date.
- Keep spare couplings, seals and fittings in stores so repairs are not delayed.
- Repeat the total-loss test at a fixed interval and plot the trend.
- Include leak checks in preventive maintenance routes and new-machine commissioning.
- Report the results in simple terms such as air lost and running hours saved, using measured figures only.
Leaks on portable and site equipment
Leakage is not only a factory problem. On construction, drilling and blasting sites, damaged hoses, worn claw couplings and poorly clamped connections waste air from portable diesel compressors and also create a whipping-hose hazard. Daily hose and coupling checks, safety whip restraints and correct hose sizing matter as much as any survey in a plant.
How Reddy Compressors helps
From Tarnaka, Secunderabad, our service team works across Telangana and Andhra Pradesh, and we supply compressors, rentals and spares across India. For leak management we:
- Carry out ultrasonic leak surveys, tagging and photographing each leak with a numbered register.
- Measure total leakage using load–unload, pressure-decay or flow methods, and record the conditions so tests can be repeated.
- Repair leaks in the compressor room and on the distribution system, and supply couplings, hoses, drains and fittings.
- Check condensate drains and compressor-room equipment for hidden air loss.
- Review generation pressure, compressor control and sequencing once leaks are under control, across ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Sullair, Doosan, Kirloskar and other brands.
- Re-survey on a schedule, often as part of an audit or AMC.
We are an independent multi-brand specialist, so our recommendations are not tied to selling any one brand of compressor.
What to send us
- Number, make and model of compressors, with rated pressure and capacity.
- Normal working pressure and the pressure seen at the far end of the plant.
- A site layout or rough sketch of the main air lines.
- Production hours and when the plant has no air demand (for a total-loss test).
- Receiver sizes and any existing flow meters or energy meters.
- Any earlier leak survey report or register.
Frequently asked questions
How do I find air leaks in my factory?
Large leaks can be heard during quiet periods or found with soap solution. For a thorough survey, an ultrasonic leak detector or acoustic camera finds small leaks even while the plant is running and noisy. Each leak should be tagged, photographed and entered into a register so that it is actually repaired and later re-checked, rather than simply being found and forgotten.
How do I calculate compressed-air leakage?
Two simple methods are common. With all users stopped, a load–unload compressor’s leakage is roughly its delivery multiplied by load time divided by total cycle time. Alternatively, stop the compressors and time the pressure decay from a known volume; leakage is about volume multiplied by pressure drop in bar, divided by atmospheric pressure and the time taken. Always record the pressure and conditions.
Can an ultrasonic leak detector measure leak flow?
An ultrasonic detector is excellent at locating leaks, and some instruments estimate flow from the signal. Those estimates depend on distance, angle, pressure and leak shape, so they are approximate. For an accurate total figure and for proving savings, combine the survey with a load–unload test, a pressure-decay test or a flow meter on the main header.
How often should a leak survey be carried out?
It depends on the plant, but leaks return steadily as hoses age, fittings are disturbed and machines are modified. Many plants benefit from a full survey at regular intervals plus routine checks during preventive maintenance. Trending the total leakage figure tells you whether the interval is right: if losses rise quickly between surveys, survey more often.
Does lowering system pressure reduce leaks?
Yes. Leak flow through any opening rises with pressure, so lowering generation pressure reduces the air lost through every remaining leak and also reduces compressor power, at about 7% per bar as a typical figure. Pressure should only be lowered after checking that every critical user still receives enough pressure, which is why pressure profiling usually comes first.
Are condensate drains a source of air leaks?
Very often. Timer drains set to open too long, float drains held open by debris and manual valves left cracked open all release compressed air continuously. Because people expect drains to hiss, these losses go unnoticed. We include every drain in a leak survey and recommend level-sensing drains at high-load points.
Related pages
Calculators and worked examples
These tools give indicative figures for screening, comparison and for preparing an enquiry. They run in your browser and send nothing. No prices or tariffs are assumed: enter your own to see costs. Efficiencies and other figures shown are example values: replace them with your own. Results are not a performance guarantee or a design certificate; final selection is confirmed by a service engineer against the machine data sheet and the site.
System leakage test: Load/unload timing, residual flow or pressure decay
Turn a non-production leakage test into a leakage flow, a share of compressor delivery, leak power and annual energy. Choose the method you used; only that method’s inputs are read. Optionally enter the result after repairs, or the measured station power before and after, to state the reduction.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Test method: Load/unload timing (fixed-speed compressor)
- Compressor actual delivered air, FAD (m³/min): 10
- Load/unload: loaded time per cycle, averaged (s): 30
- Load/unload: unloaded time per cycle, averaged (s): 70
- Residual: measured flow with production stopped (m³/min): 5
- Residual: verified legitimate continuous users (m³/min): 1.2
- Decay: system volume, receivers plus pipework (m³): 5
- Decay: start pressure (bar g): 7
- Decay: end pressure (bar g): 6
- Decay: time for the pressure fall (s): 60
- Atmospheric pressure (bar a): 1.013
- System pressure during the test (bar g): 7.5
- Normal operating pressure to restate the result at (bar g): 7.5
- Leakage after repairs, same method and pressure (m³/min; 0 if not yet measured): 0
- Station specific power (kW per m³/min): 6.5
- Pressurised hours per year: 6000
- Optional: station power in the idle test before repairs (kW; 0 to skip): 0
- Optional: station power in the idle test after repairs (kW): 0
- Idle (non-production) hours per year for the measured power: 2000
Result
- Loaded share of the cycle: 30% T ÷ (T + t) = 30 ÷ 100 s
- Estimated leakage at the test pressure: 3 m³/min free air = 50 L/s = 105.9 cfm (load/unload)
- Leakage as a share of compressor delivery: 30% of 10 m³/min
- Leak power at the operating pressure: 19.5 kW at 6.5 kW per m³/min
- Leak energy per year: 1,17,000 kWh over 6,000 pressurised hours
- Leak energy cost per year: Enter your electricity tariff (cost per kWh) above
Method. Load/unload timing (fixed-speed load/unload compressor, production stopped, timed over several cycles): leakage ≈ FAD × T ÷ (T + t), with T the loaded and t the unloaded time per cycle. Residual flow (flow meter, production stopped): unexplained residual = measured residual flow − verified legitimate users (dryer purge, instrument air, drains); it is the figure to investigate, not automatically all leakage. Pressure decay (compressors stopped and isolated, no users): leakage in free air ≈ V × (p_start − p_end) ÷ (p_atm × time), with V the receiver plus pipework volume in m³, pressures in bar and time in minutes; the pressure difference is the same in gauge or absolute terms. Leak flow through an orifice rises roughly in proportion to upstream absolute pressure, so a result taken at one pressure is restated at the normal operating pressure by × (p_op + p_atm) ÷ (p_test + p_atm). Leak power = leakage × station specific power (kW per m³/min); annual energy = power × pressurised hours. The after-repair figure must come from the same method at the same pressure. The measured-power option gives (kW before − kW after) × idle hours, which is a measured saving, not an estimate. Money is shown only when you enter your own tariff.
What to take from it. Record the method, the pressure and the plant state with every result, so the next test is comparable. A lower leak flow saves energy only if the compressors then unload, slow down or stop.
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.