Meeting Standards for Compressed Air for Railway Systems

Posted on: April 23, 2020

If there’s one thing that train passengers have in common with shippers of interstate cargo, it’s a reliance on trains to ensure a smooth journey to each destination. None of this would be possible without the availability of clean compressed air, which powers many of the most vital functions in rolling stock of all lengths and capacities.

The components of a train that rely on compressed air include the brakes, doors, and suspension system. Without compressed air, a train would be unable to halt when needed, open and close its doors properly, or offer smooth rides for passengers and cargo. Each of these functions can slow and ultimately fail if impurities enter the compressed air that is used to power the doors, brakes, and other components.

The trouble starts with dirt particles and moisture, which are present in the atmospheric air that a compressor utilizes for air compression. When these elements mix with the lubrication of a compressor, the properties of the oil change in composition. As a result, the compressor’s lubrication takes on a whitish, pasty character that lacks lubricating qualities. If the situation is left untreated, disaster can ensue, because a compressor needs lubrication in order to function properly.


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How to Maintain Standards for Compressed Air in Trains

When it comes to the standards for compressed air in railway systems, maintenance is everything. If a train’s air compression system isn’t properly maintained, it’s likely to lead to unexpected breakdowns and costly repairs. Worst of all, a train can get sidelined and be unable to service passengers or move rolling stock. For all parties concerned, the failure of a train’s air compression system is a losing situation.

The solution, of course, is to stop compressed air from becoming contaminated in the first place. This can be accomplished in the following ways:

  • Water separation and filtration
  • Compressed air desiccation


The former protects an air compressor from impurities in the atmospheric air, while the latter removes vapor from compressed air. With dirt and moisture removed from the equation, railways can rely on compressed air systems for unimpeded power to the key functions of each train for many years to come.

In recent years, increased awareness over the detriments of air contamination has spurred the development of advanced filtering systems for compressed air. The trend has gained steam in tandem with the move towards conservation and energy efficiency, both of which have been aided by the widespread adoption of pneumatic tools and machinery.

Sources of Contamination in Air Compressors

In order to enact the process of purification, it’s important to be familiar with the different types of air contaminants and where they originate. Contamination basically stems from three main sources:

  • The atmosphere. Regardless of the setting, the inlet valve of an air compressor sucks in ambient air, which will invariably contain some amount of impurities, be it dust or moisture.
  • The compressor itself. Contaminants can also originate from within the machine, though the types of germs may depend on the functions being performed. Common culprits include stale lubricant, wear particles, and coolant.
  • The air receivers and pipes. While the purpose of these parts is to collect and distribute air, both can retain marks of the contaminants that are brought into the compressor from the atmospheric air. Furthermore, the cooling that occurs in the receivers and pipes can be a cause for condensation — a major problem for the machine and the compressed air — if the machine isn’t drained on a regular basis.


The contaminants that can degrade the quality of compressed air consist of particles in the atmospheric air, as well as oil and particles in the water.

Different Types of Contamination in Air Compressors

The following types of contamination are common:


railway compressed air

  • Water vapor. With the changes in temperature that air is put through during the compression process, moisture within an air compressor is inevitable. If the air is hot, it will retain vapor; if the pressure is high, the air will release condensed water.
  • Condensed water and aerosols. During the latter stages of the compression cycle, the air is cooled to a more reasonable temperature. This turns the vapor in the air to water, which is then sent to the condensate drain. However, condensate remains a factor throughout the process, because vapors are present as the air changes temperature. Condensation is not only bad for the internal mechanisms of a compressor, it can be even more damaging if the drain is never emptied.
  • Corrosion and pipe scale. As condensation takes its toll within the piping and air receivers, rust can form on the inner lining. Gradually, the rust can cause the piping to clog and break. If the problem is left untreated, internal corrosion can lead to outright system failure.
  • Oil. Compressed air should always be oil free. Nonetheless, oil serves as a necessary evil in the process of air compression. As such, the process has its share of potential consequences. As the air is compressed, oil is used for the purposes of cooling, lubrication, and sealing. Unfortunately, up to half of the degraded oil can pass through the system in vaporized form, especially when temperatures are high. The system itself can also draw unburned hydrocarbons, which condense once cooled. When acidic oil vapors mesh with moisture in the compressed air, corrosive buildup forms along the air receivers and valve cylinders.


It must be noted that oil-free compressors are not contaminant-resistant compressors. In other words, the inlet valve of an oil-free compressor cannot magically filter out airborne contaminants from ambient air. Just as with an oil-lubricated system, an oil-free compressor needs filtration to keep water, dirt, unburned hydrocarbons, and other impurities from the compression process.

Moisture, Dirt, and Oil Filters for Air Compressors

With the various forms of air and system contamination now identified, the methods of filtration and purification can be explained in greater detail.

Water separators. In systems where air is cooled throughout the air receivers and pipes, separators are used to filter out moisture. At its most successful, the method can remove up to 92% of liquid impurities from the process of an air compressor.

Coalescing filters. Out of all the components used to purify compressed air, none are more crucial than the coalescing filters. Through a method of mechanical filtration, the component removes oil and water moisture from compressed air. Additionally, coalescing filters can remove airborne dirt particles as small as 0.01 micron. The coalescing filtration component consists of two parts in the following order:

  • The general purpose filter
  • The high efficiently filter


The purpose of the former is to prevent bulk contamination from reaching the latter. A high-quality set of coalescing filters will generally provide the twofold benefit of offering unbeatable air purity while keeping operation bills low. Furthermore, coalescing filters reduce the need for maintenance on air compressors.

Adsorption dryers. An adsorption dryer uses regenerative desiccants to filter vapor from compressed air as it passes through the system. Designed solely to remove vapor from air, adsorption dryers work in tandem with coalescing filters, but are incapable of performing the complete process of filtration alone.

Dust removal filters. An alternative to coalescing filters, dust removal filters eliminate carryover dirt from preceding junctures in the process of air compression. Using near identical filtration mechanisms to coalescing filters, the dust removal component has a roughly 99.9999% success rate at particle elimination.

The process of filtration can be split into five stages, each of which is accomplished by its own component:

  1. Water filtration
  2. General purpose filtration
  3. High efficiency filtration
  4. Adsorption air drying
  5. Dust filtration


During the first three stages, up to 92% of contaminants are removed from the air. The air is then dried during stage four, and finally removed of all dust particles during the last stage.

When Air Compressors Fail in Railway Systems: The Consequences

For railway systems and passengers alike, there are numerous consequences for not meeting compressed air standards, which are determined by the needs of a train’s pneumatic functions.

Failing doors. Passenger trains load and unload hundreds of passengers at any given stop. Therefore, it’s crucial that doors operate without a hitch at each departure point, stop, and final destination along a route. If a door fails, the consequences are threefold:

compressed air for railways

In an emergency evacuation scenario, door failure could prove fatal. The importance of door operation is also crucial in freight trains for the loading and unloading of cargo to various destinations across the United States.

Pantographs. On locomotives and light rails, air compressors are relied upon for movement to each destination due to the mechanisms of pantographs, which depend on compressed air for power. Pantographs are needed to draw currents from overhead catenary wires along railway tracks. When pantographs fail, a train might halt at the most inopportune time or place. In short, this could result in the following scenarios:

  • Light rails get backed up and cause commuter delays
  • Trains lose power in desolate areas
  • Trains or light rails halt unexpectedly at intersections


Basically, if pantographs don’t receive pneumatic power as needed, a locomotive or light rail could end up with many irate customers.

Brakes. In trains and automobiles alike, brakes are more than the stopping mechanism — they’re the most important of all emergency features. If a train can’t brake as needed, danger ensues for the passengers onboard, as well as for people, animals, or objects that might be in the train’s trajectory. In worst case scenarios, brake-failure could lead to:

  • Light rails failing to break for crossing traffic at intersections
  • Trains crashing or colliding with one another
  • Failure to halt properly at stations


For obvious reasons, it’s paramount to meet standards for compressed air in railway systems, so all brakes function to full expectation without fail.

Suspension systems. In trains of all lengths, compressed air is used to power the suspension system, which is responsible for the running smoothness of rolling stock along the tracks. When air compressors fail to deliver as needed, rides become turbulent, uncomfortable, and possibly dangerous.

compressed air brakes in railway systems

The Importance of Air Compressors in Today’s Rolling Stock

Air compression is one of the most vital sources of power in today’s eco-conscious world, where people in general have come to demand greater efficiency and energy conservation. As nations work to move away from fossil fuel, the potential offered by compressed air has grown in favor across numerous sectors. By powering a vast range of functions with compressed air, the machinery involved in the process has allowed companies to cut back on energy consumption and utilize power that is far friendlier to the environment.

In the transportation industry, air compressors are used to run rolling stock along railway tracks and provide numerous functions that ensure the convenience and safety of passengers and crew. In a sense, air compressors lie at the root of today’s railway industry, because modern day locomotives not only run in large part on pneumatic power, but are also built with the technology. At assembly plants, most of the tools used in the production of rolling stock are powered by air compressors.

In recent decades, air compression technology has seen a string of innovations, the likes of which have spurred the adoption of air compressors and pneumatic tools by untold numbers of companies. Leading the way in most of these advances is Quincy Compressor. For nearly a century, Quincy has been at the forefront of innovations in air compressors for a vast range of commercial, industrial, and automotive applications.

Much of the compressed air that drives today’s rolling stock is provided by machines that bear the Quincy name. Likewise, the tools that are used to assemble, paint, and repair modern-day locomotives are mostly purchased from Quincy.

standards for compressed air in railway systems

Quincy: The Leading Source for Railway Air Compressors

If you operate an assembly plant that produces rolling stock of any type, make Quincy your go-to source for air compressors large and small. Alternately, if you run existing rolling stock that is currently lagging due to an inability to meet the standards for compressed air in railway systems, have the current machinery replaced with Quincy air compressors. Our compressors make it possible to go the distance for years on end, regardless of speeds, heights, or humidity.

In North America and abroad, Quincy is revered for making air compressors and pneumatic tools that have brought ease and reliability to a range of tasks that were long-thought difficult across the industrial sector. To find out more about Quincy air compressors and related products, visit our sales and service locator page and see what our machines can do for your operations.