Air Dryer Buying Guide

Mar 15, 2018

Table of contents

In addition to learning about the primary types of air compressors and how to choose between them, it’s also important to learn about what varieties of air dryers are available. Like air compressors, there are many different types of air dryers, and each one offers unique features that make it suited for different purposes.

Why Are Air Dryers Important in a Compressed Air System?

Air dryers are commonly found in manufacturing plants, being used to help with day-to-day operations. They can also be found in many naval applications as well. Air dryers are essential when you have an air compressor, regardless of the type. Air compressors produce a lot of moisture and, while excess moisture can be drained, it can't be entirely removed. Water often sticks around as a vapor or aerosol, which is challenging to remove. Air dryers can help remove the excess moisture in the air from air compressors.

In many cases, any problems with your air compressor are often caused by the accumulation of excess moisture. Excessive water in compressed air systems causes operational problems such as freezing of outdoor lines, fouling of processes and corrosion of equipment. Drying prevents water from forming downstream, where it can cause product spoilage, operating problems and costly repairs.

Compressed air dryers are devices that take compressed air and remove the water vapor from it. By concentrating water vapor, the air compression causes condensation as the air cools downstream. A variety of commercial and industrial facilities use these devices.

A compressed air dryer prevents moisture from condensing by lowering the pressure dew point to a point lower than the temperature to which airlines are exposed. The pressure dew point — evaluated at 100 pounds per square inch gauge — is the temperature at which moisture begins to condense at a given pressure. The lower the dew point, the dryer the air. If the goal is to eliminate corrosion in the air system piping, you should consider a pressure dew point of -20 degrees Fahrenheit or less.

You can tell whether your air compressor system needs an air dryer by looking out for these signs:

  • The manufacturer label on your air compressor specifies the need for dry air.
  • Rust or corrosion starts to appear on parts of your system, such as the pipelines.
  • Water vapor or liquid comes out of the exhaust, hoses or lines.
  • You can identify water spots on your system's air tools.

An air dryer will help prevent your compressed air system from taking unnecessary damage that can impact operations and require expensive repairs or replacements. When operations halt due to damaged equipment, this delay can impact your productivity since you'll have to spend time and money getting everything up and running. Because of this, it's essential to place a high value on compressed air dryers to extend the life of your air compressor and increase productivity.

Types of Air Dryers

Compressed air dryers come in multiple different forms, but before you can choose the right air dryer, you need to understand how your air compressor works and what the needs of your business are. Use the following information to help you narrow down your options for an air dryer:

  • The intended use of your compressed air system
  • The air temperature requirements
  • Dew point pressure requirements
  • The operating environment of the air compressor
  • The frequency that the compressed air will be used

The specifics will vary based on the needs for your operation and the manufacturing information provided with your air compressor. Once you have all of this information, you can make an informed decision about what air dryer you'll need.

Some industries might require multiple types of air compressors, which means they'll need multiple types of air dryers. Even smaller operations can benefit from investing in a compressed air dryer system since the equipment can help increase your production volume.


types of air dryers for air compressor


There are five main types of compressed air dryers you can choose from:

Desiccant Dryers

Regenerative desiccant dryers — also known as regen dryers, twin tower dryers, pressure swing dryers or temperature swing dryers — soak up moisture on non-liquid desiccants like silica gel, molecular sieves or alumina. Moist air passes into the desiccant bed of one tower at the same time as a second tower dries or regenerates, the desiccant.

Desiccant dryers guard control and instrumentation systems, moisture-sensitive operations and laboratory equipment. They’re useful when an application requires the maximum dew point performance — which can vary from -40 to -100 degrees Fahrenheit. This low dew point protects against airline freezing in the most severe weather conditions. Desiccant dryers should also be used for applications requiring flow rates over 100 standard cubic feet per minute, or SCFM.

There are three possible methods for reviving the desiccant bed.

  1. Heatless: When renewing the desiccant bed, heatless dryers employ compressed air to expand the atmospheric temperature enough to dry out the desiccant. Heatless dryers are safer because they don’t require high temperatures or voltages. In addition to being safer, they’re the least costly desiccant dryers, which are ideal for systems smaller than 2,000 SCFM. However, they can lead to high costs in bigger systems because the cost of air required is proportional to the size of the system. The desiccant in heatless dryers lasts from 10 to 15 years with an oil-free compressor.
  2. Internal heating: Heated desiccant dryers apply electrical resistance to dry out the desiccants, and are primarily used in the 500-3,000 SCFM range. These dryers are more expensive than heatless dryers, due to the number of additional components. The more complicated controls may require additional skilled personnel to maintain them. Heated dryers can accelerate the aging process of absorbent material, requiring new desiccant material every three to five years.
  3. External heating: Blower-purge compressed air dryers dry the desiccant bed without the need for compressed air by opting for an outside blower to push heated air into the regenerating tower. Blower units tend to be the most expensive and are used in bigger systems — typically ones that are over 3,000 SCFM. When there’s a larger desiccant bed, it’s technically challenging to conduct heat evenly without using many heaters. It’s easier to heat the desiccants more evenly when using a blower.

Membrane Dryers

With a dew point range of 20 to 60 degrees Fahrenheit, membrane dryers use a dehumidification membrane that removes water vapor from the compressed air. The variance of the compressed air flow rate and pressure controls the drying power of the membrane. Membrane dryers are quiet, have no moving parts, require no electricity to operate and can operate continuously. They require little maintenance, apart from changing the pre-filter cartridge twice a year. Membrane dryers are ideal for applications requiring dew points of 35°F to 52°F and flow rates up to 600 SCFM.

Point-of-Use Dryers

Point-of-use dryers are compact, low-maintenance, plug-and-play dryers that provide clean, dry air where it’s needed most: the point of use. With a dew point range of -40 to -100 degrees Fahrenheit, they can run for up to 12,000 hours between desiccant replacements. Like membrane dryers, they require little maintenance, apart from pre-filter cartridge replacement.

Refrigerated Dryers

Refrigerated dryers are the most commonly used dryers. They operate by condensing water in a heat exchanger, cooling air enough to condense the entrained moisture and separating it from the air supply. The cold, separated air is then reheated and discharged from the system.

Refrigerant dryers provide a constant dew point range between 38 and 50 degrees Fahrenheit, regardless of fluctuations in inlet temperature. They can’t achieve dew points below freezing. When operating such a dryer in dirty environments, it’s recommended to use a water-cooled condenser.

Refrigerated dryers run continuously, which permits immediate response to airflow demands. They’re used for applications that require constant use at full capacity, although enough low usage can cause problems. Cycle-type refrigerated dryers don’t respond as quickly, but they use less power and conserve energy when air consumption is low. Cycling refrigerated dryers are ideal if you don’t plan to consistently use your compressor at full capacity.

Deliquescent Dryers

Deliquescent dryers use tablets to attract moisture and then dissolve. They produce a dew point range of 40 to 80 degrees Fahrenheit, which is directly related to inlet-air temperature, as it reduces dew point by a fixed amount below inlet-air temperature. Operating costs are directly proportional to air use, consuming no desiccant when there’s no air demand. Deliquescent dryers, however, require daily refilling with deliquescent tablets.

How to Choose the Right Air Dryer: Things to Consider When Choosing an Air Dryer

Choosing the right air dryer will increase system efficiency, increase productivity and reduce downtime. When considering the purchase of an air dryer, the following considerations may be useful:

  • Flow rate: Choosing the right air dryer depends on the maximum capacity of your air compression system. Capacity is determined in SCFM at 100 PSIG and can also be approximated by multiplying the air compression horsepower times four.
  • Operating pressure: The best air dryer for your needs also depends on the minimum and maximum operating pressure of your system. Dryers are rated at 100 PSIG. For every increase from 100 PSIG, capacity is reduced. As pressure increases, moisture load decreases, reducing strain on the compression system.
  • Air inlet and dew point temperature: You should also consider the minimum and maximum operating air inlet temperature, based on your system, and then determine the dew point requirements. The best dryer type will meet those requirements, working effectively at a dew point temperature below the lowest ambient temperature to which the compressed air system may be exposed. You can calculate the required dew point temperature by taking the lowest air temperature and lowering it by 20 degrees. While refrigerated dryers are sufficient for most purposes, critical applications requiring low moisture in the air line may require a desiccant dryer.
  • Ambient temperature: By determining the minimum and maximum operating ambient air temperature of your system, you should be able to choose between a low-temperature dryer and a high-temperature dryer. Ambient temperature above 100 degrees Fahrenheit may exceed the maximum inlet temperature of your dryer. Consider larger driers or high-temperature driers, which can withstand higher ambient temperatures during summer months. The ideal pressure dew point for your air system should be lower than the lowest ambient temperature experienced at your facility. If not, moisture will condense in the air lines. You should consider whether air lines are exposed to outdoor temperatures in summer and winter or through air-conditioned areas.
  • Application and environment: A significant factor in choosing the right type of dryer involves consideration of air usage. Most applications can use a refrigerated dryer, which produces air with 10 to 20 percent relative humidity. Desiccant dryers, on the other hand, produce less than 0.5 percent relative humidity in the outlet air, and are used in higher-quality air instrumentation applications that require a pure stream of air.

Other factors to consider include weather, indoor vs. outdoor use and location. A quality air compression company should be able to help determine the best air compressor and air dryer for your facility.

Choosing the Best Air Dryer Company

When purchasing an air dryer, consider the following questions when choosing a compressor company:

  • How long has the company been in business?
  • Does the company manufacture machines, or is the company only a reseller?
  • Does the company sell accessories for their machines?
  • Does the company have a quality service network?
  • Does the company have a broad distribution network?
  • Does the company have a good reputation for building quality machines?
  • Are they knowledgeable about air compressors and air dryers?

With more than 40 years of experience as a market leader in air pressurization and compressed air treatment systems, Fluid-Aire Dynamics offers one of the most comprehensive parts and service networks in the industry. We have a full line of air pressurization equipment for a variety of industries, including telecommunications and electric utility, and we also offer state-of-the-art design, maximizing reliability with reduced operating expense. 

Choose Fluid-Aire Dynamics for Your Air Dryer and Air Compression Needs

Fluid-Aire Dynamics offers a wide selection of air compressors. No matter what your needs are, we have something to suit them. We offer only equipment and products manufactured by companies we know and trust, so you can be sure you’re getting exactly what you’re paying for.

We not only offer a wide variety of air compressors and dryers, but we also offer filters, aluminum piping, receiver tanks, condensate drains, oil/water separators, air monitoring equipment, generatorsused equipment and much more.

But our work doesn’t end with simply selling these high-quality products. We also have years of experience in installing and repairing these types of products. We offer a full slate of repair, maintenance, installations and emergency services to ensure our customers have less downtime and increased profitability.

Shop our selection of air compressors and dryers today, and feel free to contact us anytime for more information or a free estimate.

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