Compressed air leaks and what they cost

Compressed air leaks cost money every hour the compressor runs, whether anyone is using air or not. Most plants have more leakage than they think, and most of it sits in fittings, hoses and drains that are cheap to fix. Finding the leaks, putting a dollar figure on them and fixing them on a schedule is one of the simplest energy projects a facility can run.

Why compressed air is expensive

A compressor turns electricity into pressure, and it is not an efficient conversion. Most of the electrical energy that goes into the motor comes out as heat in the compressor, the aftercooler and the dryer. Only a small share ends up as useful work at the tool or cylinder. That makes compressed air one of the most expensive utilities in a building or plant, measured per unit of useful energy delivered.

A leak wastes all of the energy used to compress that air. Because the compressor has to keep making up the loss, leaks also:

• Push the compressor into longer run times and more load cycles, which adds wear and brings maintenance forward.
• Cause pressure to drop at the far end of the system, which often leads someone to raise the setpoint. Higher pressure makes every leak worse.
• Can lead to buying an extra compressor that would not otherwise be needed.

Where leaks usually are

Leaks rarely come from the main headers. They collect at the points of use and the connections between components. When you go looking, start with:

• Quick-connect couplers and hose fittings, especially ones that get unplugged and dropped on the floor
• Worn or cracked hoses, and hoses run over by carts or forklifts
• Filter, regulator and lubricator (FRL) units, including the bowls and drain fittings
• Threaded pipe joints, unions and flanges, particularly where pipe has been modified over the years
• Condensate drains that are stuck open or set on a timer that opens too long
• Pneumatic cylinders, valves and actuators with worn seals
• Shut-off valves, pressure gauges and abandoned drops that were never capped

How to find them

Listen and look

Large leaks can be heard during a quiet shift or a shutdown. A soap solution brushed on a suspect fitting will show smaller ones. Both methods miss most leaks in a noisy plant.

Ultrasonic leak detection

Escaping air makes high-frequency sound that is outside human hearing. An ultrasonic leak detector picks up that sound and lets an inspector pinpoint leaks even while production equipment is running. Some detectors also estimate the size of each leak, which helps with ranking repairs. This is the standard method for a proper leak survey.

Measuring total leakage

To see how much leakage the whole system has, measure it when no air should be in use, for example on a weekend with production stopped. Two common approaches:

• Load and unload timing. With all end uses off, record how long the compressor runs loaded versus unloaded over several cycles. The share of loaded time, multiplied by the compressor's rated output, gives a rough leakage flow.
• Pressure decay. Shut off the compressor and time how fast pressure falls in a system of known volume. This works where the compressor controls make load timing unreliable.

Both give an estimate, good enough to show whether leakage is a small issue or a large one.

Putting a dollar figure on leaks

You do not need exact numbers to make a decision. A reasonable estimate uses four inputs:

1. The leakage flow, from the measurements above or from the leak survey.
2. The compressor's specific power: the electrical input needed per unit of air delivered. This is on the manufacturer's data sheet; many manufacturers publish it in a standard CAGI data sheet format.
3. The hours per year the system is pressurized. Leaks run 24 hours a day if the compressor does.
4. Your blended electricity rate, including demand charges where they apply.

Multiply the leakage flow by the specific power to get kilowatts, then by the hours to get kilowatt-hours, then by the rate.

A worked example

The figures below are illustrative, chosen to show the arithmetic, not typical of any particular plant. Suppose a weekend load and unload test suggests about 50 cubic feet per minute (cfm) of leakage. The compressor's data sheet shows a specific power of around 20 kW per 100 cfm at its operating pressure, so the leakage costs roughly 10 kW of electrical input. If the system stays pressurized all year, that is 8,760 hours, or about 87,600 kWh. At a blended rate of $0.10 per kWh, the leaks cost in the order of $8,760 a year.

Two things change that figure quickly. If the compressor is shut off nights and weekends, the hours drop and so does the cost. If the plant raised its pressure to cover the leaks, the real cost is higher, because every end use is now being supplied at a higher pressure too. Put your own measured numbers into the same steps and you have a defensible estimate for a budget request.

Ranking the repairs

Once the survey has tagged each leak, sort the list by estimated loss and by how hard the repair is. A large leak at a quick-connect that a maintenance technician can replace in minutes goes to the top. A small leak inside a machine that needs a shutdown can wait for the next planned outage. Keeping the list in a spreadsheet or your maintenance system lets you show the total recovered as tags are closed.

Running a leak program that lasts

A one-time leak hunt helps for a while, then new leaks appear. The plants that keep the savings treat leak management as routine maintenance:

• Survey the whole system on a regular schedule, not just when someone hears a hiss
• Tag every leak found, record its location and estimated size, and log it
• Fix the largest and easiest leaks first, and close each tag when the repair is verified
• Re-measure total leakage after repairs so you can see the result
• Install isolation valves so idle lines and areas can be shut off when not in use
• Replace timer drains that waste air with zero-loss drains where it makes sense
• Remove dead legs and abandoned drops rather than leaving them pressurized

What a leak survey report should include

• A tag number, location and photo for each leak, so a technician can find it again
• The component that is leaking and the likely repair (seal, fitting, hose, drain)
• An estimated size or loss for each leak, and a total for the system
• Whether the repair can be done with the system live or needs a shutdown
• Notes on other waste found along the way: open blowing, idle equipment left pressurized, excess pressure

Common mistakes

• Fixing leaks without verifying. A repaired fitting that still leaks is common. Recheck with the detector before closing the tag.
• Not lowering pressure after repairs. The full saving often depends on bringing the setpoint back down once the system can hold it.
• Treating the survey as a one-off. Leaks return as hoses wear and equipment changes. Without a schedule, savings fade within a year or two.
• Skipping isolation. Repairs on live air lines must follow your lockout procedure. Never loosen a pressurized fitting.

Leaks are only one part of compressed air waste; open blowing and excess pressure matter too. Safety matters during any of this work: see our guide to compressed air system safety, and our page on preventive vs reactive maintenance for how leak work fits into a planned program.

How ehZee can help

Our compressed air system inspections look at the compressors, treatment equipment, piping and points of use, and can include a leak survey with tagged, ranked findings. We start by asking what the system needs to supply, then report what we found and what to fix first. If you are planning a broader efficiency effort, see energy audits explained.

Common questions