In our air compressor buyers guide, we’ll discuss the two main types of air compressors, their key traits, and the factors to consider before purchase.

Rotary screw and reciprocating air compressors are two very common types of positive displacement compressors.  Both can be found in a wide variety of applications and industries. There are however some differences between the two. It’s important to take some time to understand these differences and how they are best applied to your requirements. By doing so, you can make a wise investment in an efficient and reliable air compressor.

Reciprocating Air Compressors – Reciprocating compressors, also known as Piston compressors, can be found in variety of designs but most commonly are used in applications under 30hp. Also, when pressures over 150 psi are required a piston compressor would typically be used. Known for their durability in demanding applications, they can do well in a variety of industrial needs. They can be mounted on tanks or base mounted and driven by electric motors or gas engines. This flexibility also makes them an attractive option. The maintenance on a piston compressor should also be a consideration.  Valves, piston rings and other parts normally require consistent routine maintenance.

Rotary Screw Air Compressors – Rotary screw compressors can be very efficient and require less maintenance than piston compressors. These compressors are designed to perform best when a constant volume of compressed air is necessary at pressures up to 150 psi.  Because of their dependability and long life cycles they are usually a great fit for standard plant air. Maintenance on a rotary screw is usually just filters and lubricant. With the use of sound dampening enclosures, noise levels can be dramatically less than that of a reciprocating compressor.

After evaluating which type of compressor fits your application and requirements the best, you will then need to closely examine the factors that will help you find a quality compressor that will last and provide you with a good return on your investment.

Reciprocating Air Compressors

Considerations for reciprocating compressors:

• What are the pressure (PSI) and air flow (CFM) requirements?
  • An overloaded compressor will not last so don’t under size your compressor requirements just to be cheap.
• Will the demand be constant or will it vary?
  • Reciprocating compressors can run stop/start, load/unload or a combination of the two.
• How much storage (tank size) will be needed?
  • Adequate storage can greatly reduce the load on your compressor.
• What is the quality of air required downstream?
  • Extra treatment such as dryers and filtration may be necessary. Oil-Less reciprocating compressors are available if necessary.

Features to look for in a reciprocating compressor:

• Slower speed operation – longer service life
• Cast iron crankcase – durable construction
• Valve construction – look for disc-type valves for increased reliability
• Main bearings – look for over-sized tapered main bearings
• Extreme duty and higher operating pressures – look for a compressor with a positive displacement oil pump
• Centrifugal unloader – allows for load-less starting reducing wear on motor/engine
• Warranty – Industrial Reciprocating compressors should be built to last, make sure that your investment is backed up by a solid warranty with local support for parts and service.

Rotary Screw Air Compressors

If you’ve decided that a rotary screw compressor is right for your requirements, how do you know what to look for in one and what differentiates the good from the not so good?

Quality – the air end is the heart of your compressor, be sure it’s built with quality and backed by a long warranty.  Make sure the manufacturer has a robust re-manufactured air end program available. Other system components should be scrutinized as well.

Size and Serviceability – a small footprint is great, but make sure you can still easily service the compressor. Most packages can be offered with an integrated air dryer which can reduce space and piping requirements.

Noise Levels – newer compressor designs and enclosures can reduce noise levels, allowing greater flexibility on installation locations.

Cooling Method – will it be air cooled or water cooled? Considerations must be made on where the water will come from if it’s water cooled and how to deal with the ambient air conditions if it’s air cooled.

Fixed Speed or Variable Speed – is your demand constant or does it vary?  A variable speed compressor can offer considerable energy savings if your plant demand varies a lot.

Control Systems – there is a huge variety of controllers in the market now that can control and monitor everything, but sometimes simplicity is better.  Don’t over complicate things if you don’t have to. Take time to look at the controllers and make sure they are easy to use.

Total Cost of Ownership – be sure to consider not only the purchase price but the maintenance costs and the energy cost to operate your compressor. Energy costs can account for over 80% of the total cost of ownership.

Service & Support – a solid warranty backed up by local support for service and parts. Look for factory trained technicians that can fix your equipment quickly and professionally.

We hope our air compressor buyers guide answered all you questions but if you still need help, contact us today. Whether you’re looking to purchase, repair or maintain air compressors, you’ve come to the right place. At Lewis Systems, we welcome the opportunity to be your partner in success.

Compressed air dryers have become an integral part of most compressed air systems today.  They help prevent product spoilage, equipment malfunction and system failure.  Although they are an important piece of your compressed air system, it’s easy for them to be overlooked until a problem arises.  Here is a short list of items to keep an eye on to ensure your downstream air is clean and dry.

Refrigerated Dryers:

• Temperature Checks – Ensure the inlet and ambient temperatures are within the acceptable ranges for your specific dryer.
• Condenser Coil – With an air-cooled dryer, it is important to clean off accumulated dust and dirt monthly, and in dirtier environments, remove debris every two weeks. Water cooled units usually have a strainer that needs to be inspected and cleaned monthly.
• Moisture Separator / Coalescing Filter – Should be checked monthly to ensure proper operation. If equipped with an internal element, it should be replaced at least annually or when the pressure drop becomes excessive.
• Condensate Drain(s) – Should be checked daily to ensure the condensate is being discharged from the unit. Most electric and zero loss drains are equipped with a test button.  If a standard internal float drain is being used, it should be replaced annually.

Desiccant Dryers:

• First and foremost, desiccant dryers are pressure vessels. Make sure all safety procedures are followed when inspecting or servicing this type of equipment.  Always de-pressurize before servicing.
• Coalescing Pre-filter – Removes any remaining oil and water aerosols before the air hits the desiccant bed to prevent saturation and oil contamination. Check the drain mechanism on this filter daily.  The element should be replaced every 6-12 months.
• Particulate After-filter – Prevents downstream air system from being exposed to desiccant dust. Element should be changed at least every 12 months.
• Desiccant – Should be replaced whenever the required dew point can’t be maintained if operating conditions are correct and there are no other mechanical issues. Desiccant life is determined by the quality of the inlet air.  Installing and maintaining a proper Coalescing Pre-Filter will extend the life of the desiccant.
• Purge Mufflers – Should be checked regularly and changed annually. Desiccant dust can clog muffler elements over time, creating back pressure and restricting purge flow.
• Valves – Every “adsorption” type desiccant dryer is different in design, but they all have to switch towers and regenerate during normal operation. Always inspect the switching valves and purge valves for proper operation and follow the manufacturer’s guidelines on preventative maintenance for these valves.

If you need help maintaining these or any other parts of your compressed air system, we are here to help.  From training your own personnel, to full maintenance contracts, we welcome the opportunity to be your partner is success.  Contact us today!

Compressed air is commonly referred to as the 4th utility, which is why facility managers are concerned with the quality and moisture content of the air going into their plant. High levels of moisture (water and oil) can cause premature wear on tools, cylinders and valves as well as increase corrosion and bacteria/mold growth inside the piping network. Installing a compressed air dryer will drastically reduce the moisture content and eliminate these problems; however, selecting the correct dryer technology is important.

Refrigerated style compressed air dryers are common and operate similarly to an air conditioning unit by cooling the incoming compressed air, condensing water vapor into liquid and then removing through a separator with a drain valve. Refrigerated dryers are limited by temperature and cannot cool below 32°F (0*C), as the condensed liquid would freeze. Pressure dew point is defined as the temperature at which water vapor condenses into a liquid at a given pressure. Based on this definition, a refrigerated dryer will deliver a pressure dew point range just above 32°F. As a reference, compressed air at 38°F pressure dew point and 100 psig pressure contains 609 ppm(w) of moisture.

Types of Refrigerated Air Dryers

There are several different types of refrigerated dryers including non-cycling, cycling and variable speed dryers.  Each technology refers to the operation of the refrigeration compressor. The compressor runs continuously in a non-cycling dryer, independent of the thermal load. Similar to your home refrigerator or air conditioning unit, a cycling dryer turns the refrigeration compressor on and off based on a varying system thermal load. Your home is the thermal mass for your air conditioning unit which allows the compressor to cycle on and off. Cycling compressed air dryers utilize a thermal mass such as silica or glycol to cycle the refrigeration compressor and a variable speed drive compressor increases or decreases the speed and subsequent capacity of the compressor relative to the compressed air consumption.

To achieve a pressure dew point below 32°F, a different technology known as adsorption is required. Small beads or granules of desiccant material are extremely effective in removing moisture, similar to the small bags you might find in a new pair of shoes or jacket pocket. In the adsorption process, the desiccant media pulls the moisture out of the compressed air stream and holds it on the surface of the beads. Over time, the beads become saturated and require regeneration. During this phase of the process (commonly referred to regeneration or desorption), a portion of the dried air from the online tower/vessel is used to flow through the saturated tower to remove the moisture. As a reference, compressed air at a -40°C/F pressure dew point and 100 psig pressure contains 10 ppm(w) moisture content and meets ISO 8573 class 2.

The ISO 8573 group of international standards is used for the classification of compressed air purity. The standard provides the test methods and analytical techniques for each type of contaminant. The table to the left summarizes the maximum contaminant levels specified in ISO 8573.1: 2010 for the various compressed air quality classes.

Nano-Purification Dryer Solutions

Nano R1-Series (NXC) thermal mass refrigerated dryers utilize a reliable, simple and energy-efficient stationary silica mass dryer design to achieve a 38°F pressure dew point (ISO Class 4 moisture vapor). If you require a lower pressure dew point for high technology lab or process applications, the nano D-Series (NDL, NHL, NEX and NBP) utilize highly efficient desiccant and advanced controls to effectively remove moisture content down to a -40°C/F pressure dew point or lower (ISO Class 2/1 moisture vapor). Contact your local compressed air professional at Lewis Systems to find out which dryer technology is right for your specific application at your facility.

Guest post written by: Mark Lauterwasser, Business Development Manager at nano purification solutions. For more information, visit www.n-psi.com. 

With colder weather coming soon, compressed air systems that are subject to lower temperatures may deal with slow starting, possible control line freeze problems, and condensate lines freezing.  To help prevent some of these problems, heat lamps can be installed close to the lines to prevent freezing. Also, applying heat tracing to control and condensate lines will help.  However, keep in mind that anything installed on the lines themselves might have to be removed when the equipment is being serviced.  Here are a few quick tips:

• Check insulated areas and make sure the heat is staying inside and the cold is staying outside.
• Also check any weather stripping and replace areas that are worn out and not working properly.
• Check condensate drains throughout your system for proper operation. Excess water in your lines and freezing temperatures are not a good mix.
• Check your air intake openings to ensure they are adequately protected from increased rain and snow.

Contact us today if you need any help with addressing your cold weather vulnerabilities.

Written by: Keith Seawell, Service Manager – Greensboro branch.  Keith has been with Lewis Systems over 30 years.