It has been our privilege to meet and interview hundreds of individuals that are involved with compressed air systems. The experience has given us an insight into the problem areas that are common to most air systems.

We hope this report will give you some ideas for making
improvements in your plant.

1. Believing compressed air is cheap

Air compressors powered by electrical motors will use a
surprisingly large amount of energy each and every year of
operation. The annual power cost to operate a compressor
can equal the initial cost of the unit.

The initial purchase price of a 100 horsepower air
compressor will range between $30,000 and $50,000, depending
on the type and options. The same 100 horsepower compressor
operating 6000 hours a year (a power rate of $.07 per KW and
a motor efficiency of .90) will have an annual power cost of
$34,800.

You can determine the annual electric power cost of your
compressors with this formula. The first step is to
multiply the horsepower of the compressor times .746 times
the hours of operation times your power rate (HP x .746 x
hours x power rate). Then, divide that number by the motor
efficiency.

Everyone in the plant should be made aware of the total
power cost for operating the compressors. This is
especially important for anyone that works with air operated
equipment.

2. Air leaks

The most common opportunity to recover energy cost is to
control the compressed air leaks.

Effective leak control in an air system can pay huge
dividends. A ¼” leak in a 100 psi system will pass about
100 CFM of compressed air. This is approximately $12,000 in
annual wasted power cost based on 24 hours a day compressor
operation with a power rate of $0.07 per kW.

The process of detecting and monitoring leaks should focus
on more than the basic header and piping system. The fact
is that you will find a majority of your leaks at valves,
fittings, connections, tools and at the point of use.

It is important to remember the interdependent relationship
between air system components. Controlling air leaks will
not translate into reduced energy cost unless the compressor
controls and air delivery system are in proper working
condition.

3. Compressor controls

There are several types of control systems in operation for
reciprocating, rotary screw and centrifugal compressors. It
is common to find a variety of these in use in the same
plant.

Compressor controls make it possible for you to translate
lower air usage into lower energy cost. However, the
typical plant is operating multiple compressors at part load
which is inefficient and expensive.

4. Pressure loss in piping system

It is important to minimize pressure drop throughout the
compressed air system. This prevents you from producing
pressure that never reaches the demand point which is a
direct waste of energy.

Every pound of increase or decrease in pressure requires ½%
increase or decrease in power. Therefore, a 10 psig
decrease can save you 5% in power costs.

This amounts to $1,740 in annual savings for the 100
horsepower compressor in the earlier example. This adds up
because most Industrial plants have more than one 100
horsepower compressor.

The pressure of an air system is often raised to overcome
pressure drop. The cause is usually found to be
shortcomings in the piping system and pressure loss at the
filters and dryers. Each of these problem areas will cost
you money on an annual basis.

The following are some common problem areas:

1. Delivering air to the point of use in pipe that is too
   small. An example; using 30’ or more of 3/8” rubber hose
   rather than 1” pipe with a short hose at the tool.
2. Using “tee” pipe connections rather than 30 or 45 degree
   angle entry connections when introducing air into a flowing
   stream of air.
3. Saving money by using undersized filters and dryers that
   have a higher pressure drop.

5. Contamination from piping system

The following are two common mistakes made during the
installation of the piping system.

a) Dirt, rust and liquids are commonly found in the piping
of a compressed air system. These cause maintenance and interrupt the supply of air.

The amount of these contaminants that are carried along with the air stream will increase when the air velocity
increases. Air velocity increases as the pipe size goes
down.

It is acceptable for the interconnecting pipe (from
compressors, dryers and inline filters to main header) and
main air header pipe to have a different air velocity
specification than the piping from the main header to the
points of air usage.

The interconnecting pipe and main header should have an air velocity between 20 and 30 feet per second (not to exceed 30 feet per second). The air lines running to the points of air usage should not exceed 50 feet per second.

You can calculate the air velocity of your system. The
formula is Flow in CFM divided by compression ratio in the pipe divided by the area of pipe divided by 60. This will give you the velocity in feet per second.

b) The piping system should always take the air off the top
of an air line when running a line from a header to the
point of air usage. This will prevent condensation and
trash from migrating to the air usage equipment.

6. Poor condensation management

Condensation is the moisture that drops out of an air flow
as it cools. The condensation in a compressed air system is
a constant threat to cause expensive problems. The
following are a few examples:

1. Moisture washes lubrication from air tools and
   production equipment causing downtime and maintenance.
2. An inconsistent supply of dry air causes production
   quality problems.
3. Excessive rust and scale often forms in the air
   distribution system.
4. Water can back up into the compressor and wreck the
   machinery.
5. Air dryers can become overloaded.
6. In-line filters can be destroyed.

The problems get worse if you operate lubed reciprocating or
oil flooded rotary screw compressors, which is just about
everyone. Compressor oil makes its way into the
distribution system with the compressed air. The mixture of
oil, water, dirt and heat tends to build up a sludge that
will ultimately jam or clog production equipment, air tools
and drains.

The situation is further complicated by climate and seasonal
weather changes. This is because the amount of condensation
generated will change according to changes in the
temperature and the relative humidity of the inlet air.

Consider that a 200 horse power compressor operating in a
climate of 60 degrees F with 40% relative humidity will
generate approximately 50 gallons of condensate a day.
However, that same compressor operating in a climate of 90
degrees F with 70% relative humidity will generate
approximately 260 gallons of condensate a day.

The typical compressed air system is designed to remove
condensation at strategic locations. This means there are
drains at the aftercooler separator, receiver tank, air
dryer, in-line filters and at drain points in the piping.

The problem is that there are shortcomings with the products
being used to drain the condensation. A condensation drain
should automatically remove condensate when it appears at
the drain without wasting air or clogging.

We have found only one drain that meets this criteria. If
you want details, send an email to drain@compressorwise.com
with your mailing address. We will have the appropriate
information sent to your attention.

7. Supplying higher pressure air than is needed

The first consideration is to determine the specific
pressure required for all the air requirements in your
plant. Plants that have studied this issue often found that
they were producing high pressure air for the entire plant
just to satisfy an isolated high pressure requirement.

They solved this problem by installing a small departmental
compressor designed to handle the higher pressure. This
allowed them to lower the pressure requirement of the main
compressors and immediately save energy cost.

8. A lack of air system training

The operation and management of a compressed air system
takes the efforts and talents of many people. A decision to
work towards energy savings will require all of these
individuals to be part of the process. However, they can
not be effective if they don’t understand the cost of
compressed air and the interdependency of the components of
an air system.

The companies that have trained their people on the
importance of saving energy have reaped the biggest savings.
This type of training has a very fast payback.

The energy savings will go directly to the bottom line and
can make a difference in the profitability of any company.
Send an email to training@compressorwise.com for our
recommended training.

9. Lack of trouble shooting information

Temperature and pressure readings can organize your trouble
shooting efforts when dealing with a problem in the
compressed air system. Specifically, you can use normal
condition readings as a reference point in order to isolate
the cause of the problem.

The normal condition readings are taken on a regular basis
for historical reference and to observe any trends that
indicate the beginning of a problem. The readings are
usually taken at locations before and after air equipment
including, among others, the compressors, aftercoolers,
dryers, receivers, air tools and filters.

a) Increasing temperature in a compressed air system is one of the best indicators of a problem. If you monitor
temperatures over time, you can build a base line for normal conditions and create a model for predicting when you will have trouble with your compressed air equipment.

The most useful tool for this application is an infrared
thermometer. This is a hand held device that gathers
temperature readings by aiming at an object.

There are a couple of points to keep in mind on this issue.
The first is to be aware that you are measuring the surface
temperature, not the temperature of the oil, air or water
inside the object.

This method is not as accurate as putting a probe in the
oil, air or water. However, it is a practical way to get
information that can be used in trouble shooting.

The second point is to always take temperature readings when the compressor is at full load. This gives you meaningful information that can be compared to the design standards for the equipment.

The infrared thermometers manufactured by Raytek Corporation are considered among the best products in this industry. They have a range of products that can handle most applications.

Their website at http://www.raytek.com has some useful
details to make it easier for you to compare the options of
their tools. However, you may want to contact them directly
for help in choosing a specific tool for your application.

b) Monitoring pressure is another useful trouble shooting
tool.

The best idea we observed was the use of a single gauge that was adapted to fit in an air line quick connection. The
operator simply inserted the gauge into quick connections
that were mounted in key locations on the air system piping.

Accuracy is critical when comparing readings and trying to isolate a problem. It is important that you use a high
quality gauge.

A superior gauge for this application is a Helicoid Digital
Pressure Gauge made by Bristol Babcock
(http://www.bristolbabcock.com). They have a Series HG2000 with several different pressure ranges (0 to 20 psi, 0 to 50 psi, 0 to 100 psi, 0 to 200 psi, etc.). The different ranges each have a unique part number, so be sure of your pressure before ordering.

10. Cookie cutter approach to oil and filter changes

A preventive maintenance program is essential for maximizing
the service life of a compressor. The key is to make sure
your program matches your application.

This means monitoring filter and lubricant condition by
measuring pressure drop and by using a regular oil analysis.
This will help you create a schedule for change intervals
that will provide the best protection for your compressor.

a) Oil analysis can be a helpful tool for compressor
diagnostics. Quarterly samples of the oil appear to be more than adequate to keep an eye on normal wear.

There are many good labs available for oil analysis. One of the leaders in this field is CTC Analytical Services. You
can visit http://www.ctclink.com for more information on
their services and a location nearest you.

b) The best way to determine when to change your inlet air
filters is to measure the restriction in the piping between
the filter and the intake of the compressor. This
restriction can be monitored by a water manometer, an intake filter indicator or a dial gauge that is calibrated in
inches of water.

The idea is to service the filter when the monitor reaches a
certain level of restriction. This specification can vary
between 10 and 20 inches of water because of the different
designs of filters. We recommend that you get a guideline
from a filter vendor that is knowledgeable about
compressors.

A final thought

Don’t rely solely on the advice of equipment vendors when
considering making improvements to your compressed air
supply. Get a second opinion.

Want to talk to an independent consultant that does not sell
equipment? If so, send an email to
advice@compressorwise.com with your question.

We will refer you to a specialist that can handle your
request. Be sure to include your phone number and the best
time to reach you.

This report, our newsletter and our website at
http://www.CompressorWise.com are dedicated to helping
industry with information about how to get the most from
compressors and compressed air systems.

The information in this newsletter and on our website comes
from Mechanics, Maintenance Supervisors, Buyers, Plant
Managers, Engineers, Compressor Consultants and others. In
no event shall CompressorWise.com be liable for any damages
arising in any way out of the use of the information.