Under pressure

From the October 2021 print edition

Air compressors are a common piece of equipment found in a variety of industries and operations; from portable handheld units found in many fleet vehicles for emergency tire top ups to portable diesel units used on construction job sites and full-size centrifugal compressors commonly used in blow molding manufacturing.

There are four main types of air compressors used in industrial applications: centrifugal, rotary screw, reciprocating or piston and process gas. There are other types available as well which are employed in specialized applications such as rotary vane and scroll air compressors.

Centrifugal air compressors are used in process applications such as air separation and blow molding tasks. This equipment creates compressed air by compressing that air through increasing and decreasing the air speed. This is done by drawing air into the centre of a rotating impeller and leveraging centrifugal force. Centrifugal air compressors are widely used in industries such as chemical plants, oil refineries and in applications involving gas and liquids like natural gas pipelines and gas turbines. Centrifugal compressors are also used in air separation applications, where the equipment separates the oxygen and nitrogen from the compressed air.

Rotary screw air compressors can be further segmented into oil-flooded and oil-free as well
as single-stage and two-stage. Oil-flooded rotary screw compressors are common in industrial applications such as general industry and automotive applications. This equipment is available with variable speed drives, generally operates quieter and are more long lasting than their oil-free counterparts. Oil-free air compressors are common in manufacturing applications such as the production of electronics, food and textiles. Single-stage compressors are often smaller than two-stage units and produce sufficient air to power pneumatic tools in light industrial applications (up to 130psi). For more demanding applications up to 170psi, a two-stage air compressor is a more efficient unit to operate. Rotary screw air compressors use a series of interlocking screws to create the compressed air.

Reciprocating air compressors are commonly used in smaller applications such as workshops, auto body shops, small businesses and home do-it-yourself projects. This equipment uses pistons to compress the air in preparation for its use. Reciprocating compressors are generally smaller air compressors that are limited to up to 10hp. These units come in single-stage and two-stage configurations in addition to portable and lubricated system options. Reciprocating air compressors offer easy maintenance and servicing of replacement parts.

Process gas air compressors pressurize and circulate gas through a process that enhances conditions for chemical reactions. Process gas air compressors also provide inert gas for safety and control systems. This equipment is found in operations that require pressure boosting and vapor recovery process. Process gas air compressors are frequently used in natural gas gathering, natural gas liquids (NGL) fractionation and liquefied natural gas (LNG) liquefaction. This equipment is generally used in the oil and gas industry.

Purchasing tips
To determine the right air compressor, two key factors should be considered: how it will be used and what is the required pressure. Other considerations may include extra options like dryers and filters, energy consumption and maintenance requirements.

How an air compressor will be used involves understanding the duration it will run; continuously for long periods as compared to intermittently as needed. Rotary screw air compressors are ideal for large demand users which need air continuously. For applications where the air compressor remains idle for a great deal of time, a reciprocating or piston air compressor is a good fit. Another consideration may also include if your operation requires a high level of air purity such as in electronics, food processing or pharmaceutical applications. Oil-free air compressors are ideal when compared to the most common oil-flooded types. Oil-flooded air compressors use the oil to both lubricate the equipment’s parts and seal in air while the oil-free models prevent contamination of the compressed air by stopping the oil from encountering the air.

For higher pressure applications, (above 1500psi), a reciprocating compressor is the best
solution. While lower pressure applications are best suited for screw air compressors that can handle up to 150psi. Oil-flooded machines offer higher PSI as compared to oil-free compressors.

The horsepower (HP) rating on an air compressor indicates the power output for its engine or motor. Higher horsepower creates higher air pressure. With higher PSI ratings the air compressor can store more air in its tank, allowing the user to operate air tools continuously for longer periods of time.

Additional features may also be available depending on the model and manufacturer being reviewed. Some features include ball valve drain, a roll cage, multiple couplers, thermal protection and an air-cooling system. The need for these features will depend greatly on the use of the air compressor, the environment the equipment is kept in as well as the organization’s budget.

Every air compressor comes with a drain valve in the tank to reduce excess condensation and ultimately rusting. However, a ball valve drain offers an easier-to-use drain. This offers greater convenience and comfort for increased usability.

A roll cage protects the air compressor from severe damage. They are used frequently on construction sites or other portable applications. The roll cage offers protection against accidental crushing. An air compressor with multiple couplers can be a great timesaver, allowing multiple tasks to operate at the same time without having to connect and disconnect the tools either with multiple or a single user. This is especially valuable when multiple tools are used during a short period of time in quick succession, such as construction or automotive assembly.

Thermal protection prevents the air compressor from getting overloaded and shuts down the unit when it overheats, safeguarding the equipment from damage and ultimately extending the lifespan of the air compressor. An air-cooling system ensures the pumping machinery remains cool through the equipment’s operation and contributes to extending the useful life of the motor.

Supplier choice
In addition to the air compressor’s specifications, another critical element to consider is the choice
of supplier. The seller can offer tremendous value to the purchasing process, including helping to determine the right air compressor to the application, installation and setup, product training, maintenance and repairs. Aligning with an air compressor expert is vital to the longevity of the equipment and the ongoing return-on-investment (ROI) it provides to the organization.

The right supplier will provide support not only at the beginning stages of the installation and setup of the equipment, including product training to ensure proper usage to avoid injuries and damage, but also offer ongoing support such as preventative maintenance and repairs when required. This will go a long way to minimizing downtime and maximizing the equipment’s useful life.

A strong supplier will also offer additional support such as product performance reporting and service level agreements (SLA). These differentiate a quality supplier by providing real-time reporting to ensure the most efficient operation of the equipment. This, coupled with a consistent level of ongoing support for any unexpected breakdowns with an SLA, can offer greater piece of mind and security. It can also reduce operating costs as some programs offer short-term rental options, remanufactured equipment alternatives and maintenance plans.

There are a variety of air compressors available on the market depending on a user’s needs within each organization. Although common across many industries, air compressors are as diverse in their specifications and models as they are in their uses. An air compressor can be the hub of many operations, from powering pneumatic air tools on an assembly line to powering gas turbines in an offshore refinery.

With the array of air compressors available it is critical to understand their applications to ensure alignment between business needs and the equipment’s capabilities to maximize efficiency and longevity.

Mariete F. Pacheco, MBA, PMP is managing director at FRW Services Ltd.