Air Compressor Guide

Getting the Most for Your Money

How to Select and Protect
Your Air Compressor Investment

Evaluating a Compressed Air System

Types of Air Compressors

Selecting an Air Compressor

Maintenance

Troubleshooting

Glossary and Reference Data

Provided as a service by Kaeser Compressors, Inc.

 Evaluating a Compressed Air System

Optimized Compressed Air System

Engineering expertise
This diagram depicts multiple compressors controlled by a system controller, followed by clean
With decades of combined experience air treatment and a storage air receiver with a flow controller. This setup ensures optimal use of
in compressed air systems and design, energy.
our entire team of qualified engineers is

T
o evaluate a compressed air sys- service, load, and maintenance hours.
always at your service. For specialized
systems or unique requirements, Kaeser’s
tem, you must begin at the end: Heat Recovery. Recovering and using
highly trained engineers provide expert What are your air requirements the heat generated by an air compres-
applications assistance. From complex at the point of use? Once you determine sor conserves energy. Waste heat has
installations and challenging environments exactly what type and how much air you many applications including process
to facilities with limited space, Kaeser can need, you can begin to factor-in design use, space heating, and preheating
design and lay out a system to meet the considerations, costs, and efficiencies. boiler feedwater.
specified requirements for performance Aftercoolers. These heat exchangers
and reliability. Design Considerations cool the compressed air and condense
Using specialized tools such as our much of the moisture for easy removal.
Careful planning is essential for smooth
Power Cost Analysis and Air Demand
operation. System configuration should This prepares the air for further treat-
Analysis, we can provide an accurate
take into consideration both your ment.
assessment of the existing installation as
requirements and the physical charac- Receiver Tank. If you have widely vary-
well as a contrasting view of the proposed
system’s performance. teristics of your installation. ing compressed air loads, consider a
Kaeser uses state-of-the-art CAD Air-cooled vs. Water-cooled. Air- receiver tank to boost capacity during
systems to lay out the proposed system cooled compressors have either peak periods. With a larger receiver
and produce traditional two-dimensional integrally-mounted or separate oil and tank, you can meet occasional peak
and three-dimensional drawings for project air coolers. These coolers require ade- demand with a small compressor and
execution. Variables such as distance, quate ventilation to perform reliably. For avoid high electrical demand charges.
diameters, equipment order, location, water-cooled compressors, an adequate Dryers. Removing moisture from
accessories and connections can be supply pressure and quality water must compressed air is essential for virtually
reviewed and modified, if necessary, prior all applications. Air quality requirements
be available.
to installation.
Full or Part Load. Air compressors and ambient conditions will help
operate most efficiently at full load or off. determine the type of dryer required.
Depending on your usage profile, it may Piping. Pipes must be carefully sized
be more cost-effective to purchase and arranged to minimize pressure drop
multiple compressors to accommodate and should be sloped to drain towards a
load variations. In some cases, variable drop leg or moisture trap.
frequency/speed drive controlled units Filters, Regulators, & Lubricators.
offer the best solution for part-load These should be installed at the point-
control/operation. of-use.
Sequencers. Sequencers improve the Condensate Control. Because con-
efficiency and reliability of multiple densate must be expelled from the
compressor systems. With microproces- system for reliable operation, drain traps
sor controls, they can stabilize system should be included in the system plan.
pressure and even track each unit’s Additionally, most localities require that

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any oil be separated from condensate the overall system efficiency are critical. Global Standards
before the water can be disposed of in Electrical Expense. As much as 70% of ISO 8573.1 was developed in 1991 by
the municipal system. compressed air cost is electrical. ISO (International Organization for
Booster Compressors. These com- Cooling Cost. If you are consider- Standardization) to help facility engineers
pressors efficiently increase plant air ing air-cooled compressors, factor in specify compressed air quality globally
with “Quality Classes” for solid particulates,
pressure for equipment or processes the electricity used to run cooling fan
humidity and oil. Quality classes provide an
that require up to 650 psig. motors. If evaluating a water-cooled
internationally accepted unit of measure. A
system, consider the quantity and typical pharmaceutical plant, for example,
Air Requirements required quality of the water, as well as would have a compressed air specification
Air Quality. There are many key levels treatment, electrical, and disposal costs. of ISO Quality Class 1.2.1. This is equiva-
of compressed air quality ranging from Maintenance Costs. The easier the lent to 0.01 micron particulate filtration,
-40° F (-40°C) dew point, and 0.008 ppm
shop air to breathing air. The required system is to maintain, the more you
(0.01 mg/m3) oil filtration.
air quality will determine the type of save in the long run.
filtration and drying system. Leaks and Unnecessary Demand.
Quality SOLIDS
Air Capacity. Begin with capacity Any leaks in your system will add to
Classes Maximum Particle Size
requirements and load factors for each your operating costs. Unnecessary (microns)
tool and machine that will use com- use of compressed air is wasteful and
0 as specified
pressed air. These compressed air expensive.
1 0.1
requirements are generally available Reliability. An unreliable compressed 2 1
from the equipment manufacturers. For air system can be disastrous to the 3 5
an existing system, a professional air bottom line. A lost production day is 4 15
system audit will provide valuable never made up. 5 40
information. 6 —
Air Pressure. Determine the pressure 70% of Your Long Term
required at the point of use. Pneumatic Compressor Cost is Quality MOISTURE
tool manufacturers rate tool capacities at Electricity Classes Dew Point
specific pressure ratings. The minimum °C °F

required pressure can be determined by Equipment Maintenance 0 as specified

the equation: 1 -70 -94
Pr = Pp + PL where: 2 -40 -40
Pr = Minimum required pressure, psig. 3 -20 -4
4 3 38
Pp = Pressure at point of use, psig.
5 7 45
PL = Total pressure loss, psid.
6 10 50
Total pressure loss includes any losses
at the dryers, centrifugal separator,
Quality OIL
particulate filter, oil removal filter, and oil Classes Liquid and Gas
vapor adsorber, as well as piping and Electricity
mg/m3 ppmw/w
valves. Analyze the total cost of a compressed 0 as specified
Once capacity and pressure air system and you’ll realize that power 1 0.01 0.008
requirements are known, the air cost is significant. In just one year it 2 0.1 0.08
compressor size and input power could exceed the cost of the compres- 3 1 0.8
requirements can be obtained from sor itself. Over a period of ten years, 4 5 4
manufacturers. this could consume 70% of your overall 5 25 21
6 — —
costs.
Cost of Compressed Air
That’s why it is important to investi-
You must go beyond initial cost when gate energy efficiency when considering
evaluating compressed air systems. a new compressor.
During the first year, operating costs for
compressed air can be 1½ to 2½ times
the initial purchase price of the equip-
ment. Efficiency of the compressor and

Kaeser Air Compressor Guide 3

 Types of Air Compressors

C
ompressed air is the fourth the housing mixes with the air to seal,
utility. Along with gas, electric- lubricate, and remove the heat gener-
ity and water, it is essential to ated by compression. This fluid forms a
most modern industrial and commercial thin film between the rotors that virtually
Sigma Profile Airend operations. It runs tools and machinery, eliminates metal-to-metal contact and
Airend performance is critical to the com- provides power for material handling wear. The fluid is separated from the
pressor’s overall efficiency and thus the systems, and ensures clean, breathable compressed air, cooled, filtered, and
compressor’s energy consumption and air in contaminated environments. It is returned to the injection point. The
operating costs. The Sigma Profile airend, used by virtually every industrial compressed air passes through an
developed by Kaeser Compressors, can
segment from aircraft and automobiles aftercooler to reduce its temperature
save up to 20% in energy consumption.
to dairies, fish farming, and textiles. and is ready for the air treatment
The Sigma Profile is standard on Kaeser
rotary screw compressors. Units are avail- A plant’s expense for its com- equipment.
able from 9 to 3140 cfm with discharge pressed air is often viewed only in terms
pressures up to 217 psig. Rotary screw of the cost of the equipment. Energy Types of Air Compressors
compressors produce virtually pulsation- costs, however, represent as much as Air Compressors
free air.
70% of the total expense in produc-
ing compressed air. As electricity rates Dynamic Positive Placement
escalate across the nation and the cost Centrifugal/Axial Rotary Reciprocating

of maintenance and repair increases, Use a rotat- Compress air Compress air
ing impeller to through the through the
selecting the most efficient and reliable impart velocity action of rotat- use of a
compressor becomes critical. to the air, which ing elements. reciprocating
is converted to Most common piston.
pressure. types are rotary
Rotary Screw Compressor: screw, which
The Plant Workhorse uses rotating
male and female
Rotary screw compressors operate on
rotors to com-
the principle of positive displacement. press air, and
Filtered air enters the inlet of the airend sliding vane,
which uses
where male and female rotors unmesh. radially moving
The air is trapped between the rotors vanes.
and the airend housing. This space is Select air compressors based on your plant
needs. Positive displacement compressors take
reduced as the rotors remesh on the in quantities of air and mechanically reduce the
opposite side of the airend. Thus, the space occupied by the air to increase pressure.
Dynamic compressors use the mechanical action
air is compressed and moved to the
of rotating impellers to transfer pressure to the
discharge port. Cooling fluid injected into air.

Basic Operation of a Rotary Screw Compressor

Compressed air
Fluid cooler

Air intake
Aftercooler filter
Fluid separator

Fluid injection

Fluid filter
Airend
Fluid
Compressed air Mixture
discharge
Separated fluid

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Selecting an Air Compressor

T
he heart of the compressed advantages such as flexibility in
air system is the air compres- pressure selection. Automatic belt-
sor itself. When selecting an air tensioning devices are a must to ensure
compressor, the most important factors transmission efficiency and protect
to consider are quality and reliability. bearings from excess stress.
Reflected in quality and reliability are Operating Interface: The control panel
overall costs, efficiency, and ease of must be reliable, user-friendly, and run
maintenance. The most cost-effective the compressor efficiently. It should
unit may not be the lowest priced. indicate operational status as well as
Components to evaluate in a compressor offer maintenance interval reminders,
include: diagnostic information and external
communications capability for remote
monitoring and control. Integration
Compressor manufacturers are adding
Interconnecting Piping. Look for rigid
more value through integrating system
piping with flexible connections to components. Some offer variable speed/
eliminate leaks. frequency drive for improved pressure sta-
Vibration Isolation. Vibrations can bility and energy efficiency. Dryers, filters,
|loosen fluid and air fittings as well as and drain traps are now commonly inte-
grated to reduce system installation costs
electrical connections. Some compres-
and save space.
sors mount the motor and airend on
vibration isolators to eliminate this
source of stress. Additional isolators
under the compressor package offers
another layer of vibration protection,
and for most rotary screw compressors,
these isolators eliminate the need for
special foundations.
Airend. Look at the package efficiency. Motor. Motor efficiency affects electrical
Most reputable manufacturers report consumption. Ensure your compressor
performance and efficiency using the motor meets or exceeds EPAct
Compressed Air and Gas Institute’s standards. TEFC motors offer much
(CAGI) data sheet. This reporting better protection from airborne dirt and
standard helps end-users make a one to dust than ODP motors.
one comparison between similar units. Sound Enclosures. A noise-insulated
Cooling Systems. Coolers and fans enclosure can reduce the compressor
must be sized to provide low discharge noise emissions well below safety limits,
temperatures in high ambient tempera- eliminating the need for a separate
tures. In air-cooled units, low-noise radial compressor room. This can save you
fans generally provide better cooling thousands of dollars in site preparation
while using less electricity than axial costs.
fans. Also consider the ability to easily
duct air in and out of the compressor
package. Topside exhaust often
simplifies ducting for heat recovery and
reduces footprint.
Drive. Efficiency and simplicity are
important. Direct-coupled, 1-to-1 drives
offer the best efficiency with no loss in
transmission efficiency and require no
maintenance. Belt drives require only
simple maintenance and offer

Kaeser Air Compressor Guide 5

 Maintenance

T
o most people who select an air Noise and Other Site
compressor, the most important Requirements?
factors are overall cost, efficien-
Air compressors with low-sound
cy, ease of maintenance, and trouble-
enclosures and vibration isolators
Simple Service shooting.
can save thousands of dollars in site
Kaeser compressors are designed for preparation costs. You may be able to
Who Can Fix It?
easy maintenance and serviceability. The eliminate the expense of a separate
air filter, oil filter, and oil separator are all If an air compressor system can be
compressor room or special foundation.
easy to reach, check, and replace. Special serviced by in-house personnel, overall
inlet filter mats are readily accessible. To operating costs will be less and down- What’s the Warranty?
facilitate oil changes, each rotary screw time will be reduced. The more complex
A warranty is the manufacturer’s pledge
compressor is fitted with an oil change the compressor and compressor
to the customer. Make sure you have a
pressurization valve and drain hose. The controls, the more difficult repairs will be.
doors and lid on the compressor cabinet comprehensive warranty on your equip-
Selecting the simplest system will save
allow immediate access to all maintenance ment that is backed by solid manufac-
you money.
points. turer and distributor support.
Easy to Maintain?
Proper maintenance adds to the reliabil- Maintenance Checklist
ity and efficiency of the air compressor.
A compressor that is difficult to maintain  Compressor prefilters: Check and clean or
causes problems and costs money. replace; service frequency relates to condi-
Some air compressors and air compres- tions in operating environment.
sor components are specially designed  Compressor fluid level: Should be at “full”
for easy maintenance. mark; change per manufacturer’s recommen-
dation; DO NOT OVERFILL
 Inlet filter cartridges: Remove and clean or
replace.
 Drain traps: Periodically check for proper
operation.
 Check for leaks throughout: Piping and
flexible joint packings, control lines, control
line fittings, clamps and connectors, valves,
air pressure safety relief valves, and pressure
gauge connections.
 Compressor cleanliness: Maintain in a clean
condition; a compressor should never leak
fluid.
 Coolers: Check water quality, flow, and
temperature in water-cooled units; check inlet
filters and cooler surfaces on air-cooled
models.
 Belt condition: Check for wear or damage
and re-tension as required.
 Compressor temperature: Should be within
manufacturer’s limits.
 Record service and load hours: Systems
that record both service and load hours are
easier to maintain and troubleshoot.
Refer to the service manual for recommended
maintenance schedule. Accurate mainte-
nance and operating records are essential for
smooth and trouble-free operation.

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Troubleshooting

I
n a compressed air system, as in any The troubleshooting chart below is
plant system, problems occur during not comprehensive, but indicates some
Remote Monitoring
routine operation. Most of these common problems that can develop in Sigma Air Manager combines the bene-
problems are minor and can be compressed air systems using positive fits of a modern industrial PC technology
corrected by simple adjustments, clean- displacement compressors. with Internet technology to provide
ing or replacing a part, or eliminating an unparalleled compressor control,
monitoring and reports. Optional software
adverse condition. Any major problem
provides enhanced reporting and enables
that may develop is generally related
end users to control air system operation
to improper cooling or lubrication, poor from any location.
maintenance and operating practices, or
misapplying the system.

Troubleshooting Compressed Air Systems

Problem Probable Cause Remedial Action
Low pressure at Leaks in distribution piping Check lines, connections and valves for leaks
point of use Clogged filter elements Clean or replace filter elements
Fouled dryer heat exchanger Clean heat exchanger
Low pressure at compressor See below
discharge

Low pressure at For systems with modulating Follow manufacturer’s recommendation for
compressor dis- load controls, improper adjust- adjustment of control
charge ments of air capacity control
Worn or broken valves Check valves and repair or replace as required
Improper air pressure switch Follow manufacturer’s recommendations for
setting setting air pressure switch

Water in lines Faulty air/oil separation Check air/oil separation system; change
separator element
Failed or undersized com- Follow manufacturer’s recommendation for
pressed air dryer proper oil level

Dirt, rust, or scale In the absence of liquid water, Install filters at the point of use
in air lines normal aging of the air lines

Excessive service System idling too much For multiple compressor systems, consider
to load/hour ratio sequencing controls to minimize compressor
idle time; adjust idle time according to
manufacturer’s recommendations
Improper pressure switch Readjust according to manufacturer’s
setting recommendations

Elevated compres- Restricted air flow Clean cooler exterior and check inlet filter mats
sor temperature Restricted water flow Check water flow, pressure, and quality; clean
heat exchanger as needed
Restricted fluid flow Check compressor fluid level, add fluid as
required
Low fluid level Remove restriction, replace parts as required
Excessive ambient Improper ventilation of compressor; check with
temperatures manufacturer to determine maximum operating
temperature

Kaeser Air Compressor Guide 7

 Compressed Air System Glossary
Absolute pressure: Total pressure measured Dual control: Load/unload control system that
from absolute zero. maximizes compressor efficiency. Compressor
is normally operated at full load or idle, and is
Aftercooler: Heat exchanger for cooling air stopped and restarted automatically depending on
Mission Statement discharged from air compressor. demand.
We strive to earn our customers’ trust Atmospheric pressure: Pressure above absolute Free air: Air at ambient conditions of tempera-
zero at a specific location and altitude
by supplying high quality Kaeser air ture, humidity, and atmospheric pressure at any
Capacity: The amount of air flow delivered or specific location.
compressors, related compressed air
required under some specific conditions. May be
equipment and premium blower Inlet pressure: The total pressure at the inlet
stated as acfm, scfm, or cfm FAD.
flange of the compressor.
systems. Our products are designed Cubic feet of air per minute (cfm): Volume
delivery rate of air flow. Load factor: Ratio of the average compressor
for reliable performance, easy load to the maximum rated compressor load
maintenance, and energy efficiency. Cubic feet of air per minute, free air (cfm during a given period of time.
FAD): cfm of air delivered to some specific point
Prompt and dependable customer and converted back to ambient air (free air) Modulating control: Control system which will
service, quality assurance, training, conditions. run the compressor at reduced output to
accommodate demand variations. Running a
and engineering support contribute to Actual cubic feet per minute (acfm): Flow compressor at less than full load results in a drop
rate of air measured at some reference point and
the value our customers have come to in compressor efficiency and thus an increase in
based on actual conditions at that reference point. operating costs.
expect from Kaeser. Our employees
Inlet cubic feet per minute (icfm): cfm
are committed to implementing and flowing through the compressor inlet filter or Pressure: Force per unit area.
maintaining the highest standards of inlet valve under rated conditions. Pounds per square inch (psi): Force per unit
Standard cubic feet per minute (scfm): area exerted by compressed air.
quality to merit customer satisfaction.
Flow of free air measured at a reference point
We aim for excellence in everything Pounds per square inch absolute (psia):
and converted to a standard set of reference Absolute pressure above zero pressure.
we do. conditions (e.g., 14.5 psia, 68°F, and 0% relative
Our engineers continue to refine humidity). Pounds per square inch gauge (psig):
Pressure difference between absolute pressure
manufacturing techniques and take full Demand: Flow of air under specific conditions (psia) and ambient pressure.
required at a particular point.
advantage of the newest machining Pounds per square inch differential (psid):
innovations. Extensive commitment to Discharge pressure, rated: Air pressure Pressure difference between two defined points
produced at a reference point. in the system.
research and development keeps our
Discharge pressure, required: Air pressure Pressure dew point: Temperature at which
products on the leading edge of required at the system inlet. water will begin to condense out of air at a given
technology to benefit our customers. pressure.
Displacement: Amount of air (in cfm) displaced
by the compressor piston under no load, discharg-
Pressure drop: Loss of pressure in a
ing directly to the atmosphere.
compressed air system due to friction or flow
restriction.

Rules of Thumb
Air compressors normally deliver 4 to 5 cfm per A 50 hp compressor rejects heat at
horsepower at 100 psig discharge pressure. approximately 126,000 Btu per hour.
Depending on the size of the system, Size air receivers for about 2-5 gallon capacity
Corporate Headquarters: compressed air costs about 25 to 30 cents for each cfm of compressor capacity.
per thousand cfm (including operating and
Kaeser Compressors, Inc. The water vapor content at 100°F of saturated
maintenance costs).
compressed air equals about 6 gallons per day
P.O. Box 946 Every 2 psi pressure drop costs 1% of for each 100 cfm of compressor capacity.
Fredericksburg, VA 22404 compressor horsepower in efficiency.
(800) 777-7873 Power cost for each 1 horsepower operating
Fax: (540) 898-5520 constantly for one year at 10 cents per kwh is
www.kaeser.com about $750.

Effects of Ambient Conditions on Compressor Ratings

100 120 5000
80 110 4000
60 100 3000
40 90 2000
20 80 1000
© 2011 Kaeser Compressors, Inc. 0 70 0
0 1 2 3 4 5 6 7 8 9 10 11 12
All rights reserved. 05/11 Altitude (ft.) scfm Reduction, %
USGUIDE1 Ambient Temperature (°F)
Relative Humidity (%)