How To Choose the Best Air Compressor

With the various technologies and different types of compressors available, choosing the correct one can be confusing and oftentimes overwhelming. There are three key questions to knowing what compressor you should buy.

1) What Compressor Size do I Need?

One of the biggest challenges is to correctly size your new air compressor. Similarly to everything else, new compressors available on the market are more efficient and employ better technology, therefore you have to understand the application and usage to size the machine correctly. Choosing the wrong air compressor for your facility can lead to problems with production and or increased costs due to wasted energy.

What amount of pressure do I need?

Understanding the flow and pressure requirements for your facility is key when choosing an air compressor. Pressure and flow are two very common terms used when discussing compressed air systems.

Pressure can be measured in pounds per square inch (psi), or bar (metric measure of pressure). To think of this in simpler terms, pressure refers to the amount of force needed to perform certain amount of work at any given point in time. A simple example of pressure and how it works, is to imagine moving a wooden block across a table. In the illustration below, it shows that using 75 psi of compressed air is not enough force to move the block, but 100 psi of pressure has the ability to move the wooden block the desired distance.

The air compressor has to provide enough pressure to perform a given task (in this case it was to move a wooden block). Per illustration below, if 100 psi is required to move the block, anything less than that will not accomplish the task. It is important to understand what pressure is needed in order to size the compressor properly, otherwise you will be faced with problems, similar to illustration below where lower pressure was not able to move the wooden block, or perform the job.

2) What Type of Compressor Do I Need?

Once you have the size of the air compressor figured out, the next thing to do is to decide on the type of compresor you will need for your application. Let us take a look at two of the most popular options available. 

Some questions to ask yourself

When choosing the right type of compressor, you should ask yourself these questions:

• What is the application 
• How much flow does my facility/workshop use 
• What pressure is needed within the facility 
• Do I need clean/dry air (use of dryer and filters) 
• How many hours per year does my compressor operate 
• How many shifts do I run per day 
• Is there fluctuation in flow demand between shifts (if so, a VSD compressor could be a good option and offer great savings) 
• Are there any plans for future expansion

The piston compressor

The most economical and least expensive air compressor available is the piston or reciprocating air compressor. This is a very simple and robust air compressor that is used in many small shops. You can oftentimes find the piston compressor in small work and machine shops, body shops, tire shops and small manufacturing facilities. Piston compressors are relatively easy to maintain and as previously mentioned require minimum investment. Considering that piston compressors are economical, there are some drawbacks that should be taken into account before making a decision.

The rotary screw compressor

If your operation requires constant compressed air supply, you should consider a rotary screw air compressor. Unlike the piston compressor, rotary screw air compressors are used for any operations that require up to a 100% continuous duty cycle and are built for long lifetime of reliable operation. Rotary screw air compressors are a great alternative fot the piston units and there are various available, depending on your needs and budget. One of those options is the ability to integrate a dryer into the package, which is ideal for the applications that require clean and dry air. 

Variable Speed Drive compressors are a great option for any facilities that have fluctuation in their flow demand. This is especially true if your facility operates multiple shifts during the day and where flow demand increases and decreases throughout the day. Considering that compressed air usage can be costly, as it accounts for over 70% of Total Cost of Ownership in electricity costs, utilizing VSD technology can help you achieve savings of 35-50%. Depending on size of the compressor, the savings can range from 2000 EGP to 160,000 EGP annually or more.

3) Do I Need an Oil-Free or Lubricated Compressor?

Once you have the size and type of compressor figured out, one last question remains, should I go with an oil lubricated or oil-free air compressor. To not overcomplicate the answer, your choice should be based on the application and process that the compressed air will be utilized in.

Do I need an oil-free compressor?

The first step in selecting any compressor is assessing your facility’s needs. There are instances where the consequences of oil contamination are too high, therefore having an oil-free air compressor is a must. However, the majority of manufacturing, industrial and small workshops utilize oil injected compressors, since the consequences of oil contamination are not as great as they would be in a food production facility for example. Oil in air compressors is utilized to lubricate, seal and also cool the compressed air. 

If there is no immediate need for oil-free compressed air, the more economic way is to go with an oil lubricated unit like an oil-injected screw compressor. Oil-free compressors carry a much greater cost. Although, there are traces of oil in compressed air, those can be cleaned up further by utilizing proper quality air products. The use of coalescing filters can clean the compressed air down to 0.01 micron, which can further be cleaned by adding a carbon activated filter to get close to Class 1 air purity.

What are the different air purity classes?

Oil-free air compressors are used to produce a wide range of sensitive products, from semiconductors, medication and paper. Even the smallest trace of oil in such applications could have adverse effects on products and even people. Class 0 and “technically oil-free” are often used to imply that a compressor meets certain standards. Although, these terms are similar they have key differences that if not taken under consideration can lead to unintended consequences.

ISO Class 1 - Technically Oil-Free Air

ISO Class 0 - Oil-Free Air 

When choosing an oil-free compressor, make sure to pick a Class 0 oil-free compressor and not a “technically oil-free” option. They generally have a higher initial price point, but they are much safer to use in sensitive applications. With Class 0, you can be sure that absolutely no contamination will reach your end user equipment and rest assured that your assets are protected. It is always best practice to seek advice from a compressed air professional when picking out an oil-free or oil lubricated air compressor.