Estimating the Cost of Compressed Air Systems Leaks

Leaks in a compressed air system can waste thousands of dollars of electricity per year. In fact, in many plants, the leakage can account for up to 30% of the total operational cost of the compressor. Some of the most common areas where you might find a leak would be at connection joints like valves, unions, couplings, fittings, etc. This not only wastes energy but it can also cause the compressed air system to lose pressure which reduces the end use product’s performance, like an air operated actuator being unable to close a valve, for instance.

One way to estimate how much leakage a system has is to turn off all of the point-of-use devices / pneumatic tools, then start the compressor and record the average time it takes for the compressor to cycle on and off. The total percentage of leakage can be calculated as follows:

Percentage = [(T x 100) / (T + t)]

T = on time in minutes
t = off time in minutes

The percentage of compressor capacity that is lost should be under 10% for a system that is properly maintained.

Another method to calculate the amount of leakage in a system is by using a downstream pressure gauge from a receiver tank. You would need to know the total volume in the system at this point though to accurately estimate the leakage. As the compressor starts to cycle on,  you want to allow the system to reach the nominal operating pressure for the process and record the length of time it takes for the pressure to drop to a lower level. As stated above, any leakage more than 10% shows that improvements could be made in the system.

Formula:

(V x (P1 – P2) / T x 14.7) x 1.25

V= Volumetric Flow (CFM)
P1 = Operating Pressure (PSIG)
P2 =  Lower Pressure (PSIG)
T = Time (minutes)
14.7 = Atmospheric Pressure
1.25 = correction factor to figure the amount of leakage as the pressure drops in the system

Now that we’ve covered how to estimate the amount of leakage there might be in a system, we can now look at the cost of a leak. For this example, we will consider a leak point to be the equivalent to a 1/16″ diameter hole.

A 1/16″ diameter hole is going to flow close to 3.8 SCFM @ 80 PSIG supply pressure. An industrial sized air compressor uses about 1 horsepower of energy to make roughly 4 SCFM of compressed air. Many plants know their actual energy costs but if not, a reasonable average to use is $0.25/1,000 SCF generated.

Calculation :

3.8 SCFM (consumed) x 60 minutes x $ 0.25 divided by 1,000 SCF

= $ 0.06 per hour
= $ 0.48 per 8 hour work shift
= $ 2.40 per 5-day work week
= $ 124.80 per year (based on 52 weeks)

As you can see, that’s a lot of money and energy being lost to just one small leak. More than likely, this wouldn’t be the only leak in the system so it wouldn’t take long for the cost to quickly add up for several leaks of this size.

If you’d like to discuss how EXAIR products can help identify and locate costly leaks in your compressed air system, please contact one of our application engineers at 800-903-9247.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

 

 

 

 

One For The Gearheads

EXAIR Application Engineers are geeky about compressed air, but there’s a few gearheads at heart among us, too.  I’m one of them.  Read through my blog below for a dive into my most recent gear-driven fun!

1998 A4

Recently I took on a new project at home.  One of my friends called me to tell me about an A4 with a potentially blown motor that might find a happy new home for the right (low) price.  Seeing as how I’ve procured many a vehicle in just the same way, I’m always optimistic about these kind of things.

So, I made the trip to look at the A4 and found a clean interior, 80k on the clock, and a no-start condition.  After sitting at the dealer for over a month without an accurate diagnosis, the owner had it towed to his house where he put it on the market as-is.  Unsure of the problem, but confident I could find and fix whatever is needed, I bought the car.

AHA DOHC

Cranking the engine (2.8 AHA code) over, I could hear a lack of compression, so I pulled the plugs and confirmed with a gauge.  Bank one (cylinders 1-3) had virtually zero compression on any cylinder, and bank two (cylinders 4-6) was perfect.  Interesting…  My first thought was that there was a timing belt failure and valves were bent when getting readings on bank one.  But the perfect readings on bank two made me second guess.  Nevertheless, I pulled the front carrier/core support and tore down to the timing belt.  Sure enough, the teeth of the belt were chewed off at the crank!  But, the story goes on…

The repair in a case like this is to pull the cylinder heads, check all the intake and exhaust valves for leakage, and replace those that are faulty (or all the valves depending on their condition).  Some people call this a rebuild of the top half of the engine, which is pretty accurate.

When I removed the cylinder heads and began to disassemble them, I could tell something wasn’t right.  There’s a camshaft adjustment unit used to advance or retard valve timing that has a special landing and thread for a service tool.  On the bank one cylinder head, this landing was missing (see the photo below).  Strange!  And, normally, the camshafts can be removed fairly easily once their bearing caps are removed.  But, on this cylinder head, no dice.

VVT Unit

Ultimately I found that the landing for the camshaft adjustment unit broke off and wedged on the exhaust cam of bank one.  See the photos below for the gouge mark on the casting.  This cam seized, locked everything on the head, and forced the crank to chew the teeth off the timing belt.  Miraculously, the valves on bank two avoided any damage and triple checked out when disassembled.

Head Gouge 1

Head Gouge 2

This failure led to the damage of (5) valves.  Some of them are visible to the naked eye as seen below.

Bent Valves

Now comes the fun part of getting the engine back together, knowing that there’s a “new” car at the end of all the work.

Lee Evans

Application Engineer

LeeEvans@EXAIR.com

@EXAIR_LE