How to Determine What Type of Compressor You Need
First of all, selecting an air system can be quite difficult and can be very different depending on the
specific application and need of the shop. Always consult a compressed air specialist when determining which equipment is right for you and your application. Listed below is a summary of the steps required to select the appropriate air compressor and system for your specific application.
Determine the voltage and phase where the compressor will be installed.
o Determining this prior to quoting and/or ordering your compressor as it will keep you
from having any surprises upon installation
o An example of voltage at a location would be 230 volt – 3 phase.
Determine how much air you need for your application or plant.
o How much air you need can be determined by the volume of air measured in cubic
feet per minute, or CFM. This can be calculated by adding up the air requirements of
the tools you use most frequently, divide by 35% where 35% is a utilization factor
which means that any one tool will be used 35% of the work day. This is a very quick
way to determine air demand. See example below
Small die grinder uses 7.0 cfm @ 125 psi
1/4 Inch impact wrench uses 8.0 cfm @ 125 psi
3/8 inch drill uses 9.0 cfm @ 100 psi
2 inch horizontal grinder 11.0 cfm @ 100 psi
Therefore, 7.0 + 8.0 + 9.0 + 11.0 equals a total of 35 cfm
o Next, take 35 X .35(utilization factor) = 12.25 cfm air demand
Determine the air pressure required for your application or plant.
o Look at your tools to determine their pressure requirements.
o The tool with the highest pressure requirement will be the minimum pressure you
o Most single stage compressors (including rotary screws) have a continuous pressure
rating of 125 psig maximum.
o Most two stage reciprocating compressors operate at 175 psig
o A two stage compressor can be regulated down to lower pressures
The advantage of a two stage compressor is that you store more air at a higher
pressure in an air receiver (tank).
If you look at the example above, the die grinder and impact wrench require
125 psi. This means that you require a minimum line pressure of 125 psi from
the compressor. A single stage compressor could possibly handle the
application discussed above; however, since the required 125 psi is also the
maximum output for a single stage compressor, most people would consider a
two stage compressor, which can deliver air at 175 psi.
Benefits of a two stage compressor in the applications discussed above:
More air can be stored in the same amount of space at higher
pressures, which means that a two stage compressor will not run as
often as a single stage and save you money.
The two stage compressor runs cooler than a single stage, which equals
longer compressor life and reliability.
o Now compare your requirements to the output of the compressors you are considering
to purchase. A good rule of thumb is to have a 75% duty cycle. This means the
compressor will be running and compressing air 75% of the time and off, sitting idle,
25% of the time. To determine how much air you need the compressor to deliver to
maintain a 75% duty cycle, divide your estimated air demand by .75 (see example
12.25 cfm / .75 = 16.3 cfm
So you’ll need a compressor that will deliver at least 16.3 cfm and have an
output pressure of at least 125 psi.
There are many different types of compressors in the marketplace today, reciprocating,
rotary screw, rotary vane, and many others. It is best to consult your local compressed air
specialist or contact Champion Pneumatic at www.championpneumatic.com to help determine
which compressor is best for your specific application.
How to best maintain your compressed air system
Very few pieces of equipment are used as regularly as shop air compressors. In order to ensure that your air compressor runs efficiently every day, your compressor needs proper maintenance, just like your car. When initially installing your new air compressor, it should be placed in a clean, well-ventilated area. Some facilities will place their compressor in a “compressor room” that’s apart from the general shop area. This special room may also include an external intake for clean air for the compressor and should always be well-ventilated.
A good safety precaution to protect the equipment that is run off the air compressor is to install a filter, regulator, gauge, and lubricator in your system. Filters, regulators, and lubricators come in various combinations, and are specified based on the compressor, climate, application, and equipment you will be running off the air compressor. For optimum results, these filter/regulator/lubricator assemblies should be installed in-line no less than 10 feet from the air compressor. This distance allows the air to cool before going through the filter. This allows the filter to properly do its job. Many of the machines run off your air compressor are expensive pieces of equipment and you don’t want any water to get through and create contamination or rust in the system. The filter will also eliminate any solid particles (particulate) that may be in the air line. Having a pressure gauge is also essential for maintaining pressures that fall within the manufacturers’ recommended levels. Incorrect pressure levels can impair tool performance and cause safety hazards in the workplace. A pressure gauge can also help detect any leaks that may have formed in the air lines. If there are leaks, your shop is wasting money in electricity that is required to replenish the lost air supply. Lubricators (also known as oilers) are designed to be used between the filter and equipment/machine the air compressor is supporting. They feed oil directly into the air line and provide constant lubrication for your air tools. This lubrication can significantly extend the lifespan of your tools and equipment.
As mentioned above, it is vitally important to keep the entire air compressor clean as dirt and other debris can act as an insulator and cause the unit to run hotter than necessary. Under normal use, temperatures inside an air compressor can exceed 400° F. Anything you can do to keep this temperature from escalating will help your air compressor run better and last longer.
Proper maintenance is also a key to ensuring your compressor operates smoothly. The main air tank (or receiver) on the compressor should be drained on a daily basis. The tank can be drained manually or Champion Pneumatic (www.championpneumatic.com) offers automatic devices (both pneumatic and electric) that open the drain valve for a specified period of time each day to ensure the tank is properly drained.
Compressed air creates condensation, and as such, additional daily maintenance should include draining any moisture traps in the system and opening the air valve on the drain legs of your system to remove the liquid water that’s already trapped.
It is also important to change the oil in your compressor on a regular basis. A low oil level can cause the compressor to work harder and run hotter, ultimately resulting in shorter compressor life or catastrophic failure. On average, the oil should be changed at least every 6 months or in severe applications, every 2-3 months. Every application is different and the compressor manufacturer and/or owner’s manual should be consulted to determine proper change intervals. The owner’s manual will also include recommended specific weight and brand of oil to use. Simply changing the oil at regular intervals helps keep the internal parts of the compressor well lubricated.
A safety inspection should be routinely performed on your air compressor. During this time, it is important to check the drive belts for any signs of wear. If you find damage to any of the belts, you should always replace both belts at the same time. Replacing multiple belts (if your compressor has more than one) as a matched set will ensure balanced tension from the drive motor to the compressor sheave (pulley). While inspecting the belts, the belt guard should also be checked to make sure it is doing it is serving its purpose.
Air dryers are another important part of any air system and are used to cool the compressed air after it leaves the compressor. The process of cooling of the air lowers the dew point, which turns any water vapor in the air into liquid. Any moisture or condensate is then removed from the air line as it passes through the dryer. There are a few different types of dryers on the market today, so be sure to discuss with your supplier which one best fits your shop’s needs based on what you will be using the compressed air for on a daily basis. For example, any shop that also performs body work will require ultra-clean and dry compressed air for its paint booth.