Why does my compressor system perform differently at higher altitudes?

Anyone who has had to use a compressor at a high altitude knows how frustrating it can be. Compressor performance is degraded and it can take a lot longer to complete tasks. People who move to or work in areas that are at a higher altitude are often surprised when their compressor seems to be working slower than normal.

How an Air Compressor System Works

Mobile air compressor systems commonly in use typically consist of a gas or diesel engine powering an air compressor. When you turn on an air compressor system, it draws in ambient air through the compressor intake and compresses it to a smaller volume. This compressed air can then be stored in a storage tank or used to directly power your tools and equipment. Once the air storage is full or the tools being used are no longer running, the compressor stops drawing in and compressing air by either shutting off the engine and compressor or entering some sort of a standby mode.
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Methods to Power Your Air Compressor with an Industrial Engine

There are many ways to power an air compressor using an industrial engine. Choosing the best way to power your air compressor should be decided by a number of factors, including space, existing components and systems, weight, and your available engine options. In this article, we provide an overview of the most common methods of powering your air compressor using an industrial engine.

Engine Mounted FEAD Belt Drive


Many systems use an engine-mounted “Front End Accessory Drive” (FEAD) to drive alternators, generators, air conditioning compressors, water pumps, cooling fans, and air compressors. With a FEAD setup, the auxiliary components are mounted directly to the engine and driven from a serpentine or V belt.

Air compressors that use FEAD power can do so in one of two ways:

  • in line with the existing belt system, or,
  • by adding another pulley to the crankshaft and designing another belt system

With the FEAD power method, the driven and driving pulley diameters can be customized to provide the required compressor output at a given engine speed. Belt drives can also provide some damping of potentially damaging torque pulses, which helps with system longevity.

A custom bracket will likely be needed to mount to the engine to support the compressor and if equipped, the secondary belt system components such as the idler(s) and tensioner. The air compressor itself can be driven via a clutch or fixed pulley, depending on whether it’s desirable to completely stop the compressor while the engine is running.

VMAC’s UNDERHOOD air compressors utilize the FEAD power method.

Frame Mounted Belt Drive

The FEAD system has many advantages but it can be challenging to mount an air compressor to an engine. In this scenario, a frame mounted belt drive can be an ideal alternative.
To simplify the air compressor bracket design, it can be mounted to the base frame instead of the engine. With this design, the belt is still driven off a pulley mounted to the engine’s crankshaft, but the compressor itself is located further away, where more space is available.

Typically, frame mounted belt drive systems use a V belt instead of a serpentine belt. V belts are better at handling misalignment and variations in tension, which can occur between the engine and air compressor under operating conditions—especially if the engine is not hard mounted to the frame.

For example, VMAC has co-designed the frame mounted belt drive system pictured below.


Auxiliary Port Direct Drive

Auxiliary-Port-Direct-DriveMany industrial diesel engines and some gasoline engines come equipped with an auxiliary PTO port, which is used to power bolt-on accessories. These ports are usually part of the front or rear engine cover and are driven via the crankshaft/camshaft/fuel pump gear-train.

Auxiliary ports come in various configurations usually conforming to an industry standard. The connection to the drivetrain is either a splined port or direct gear mount, depending on the sophistication of the design. Over or under drive ratios may also be available via bolt-on adaptors.

Traditionally, only small reciprocating compressors were driven by auxiliary ports. However, some higher volume rotary screw air compressor designs now take advantage of this PTO drive method too. VMAC’s PTO air compressor is one example of this type of design.

Flywheel Direct Drive

A common method of powering an air compressor is to drive it through a coupling directly off of the flywheel. This setup often uses industrial couplings, which are designed to dampen vibration and torque spikes, while forgiving some misalignment between the engine and air compressor. A speed increasing gearbox is frequently used to help generate the high RPM required for rotary screw air compressor operation. These compressors can also be coupled with an electric motor or generator.


Flywheel Belt Drive

A pulley and belt configuration can be connected to the flywheel to power your compressor, similar to the FEAD drive system described at the start of this article. However, the flywheel system isn’t as popular because there are more components to work around when using the flywheel. It’s typically easier and more straight forward to design a bracket and belt system for the FEAD.

Hydraulic Drive

If the engine or equipment is using hydraulic power for other functions, adding hydraulic power to run a compressor can be a convenient option. While not directly mounted to the engine, the use of an engine-driven hydraulic motor to power an air compressor is common.

Hydraulic power is less efficient when compared to the direct drive methods discussed above, as it may require additional hydraulic cooling capacity and will burn more fuel for a given compressor output. However, this method allows more positional flexibility between the engine and air compressor, which can be helpful if there is limited space on or around the engine.
VMAC’s Hydraulic Driven Air Compressors use this power method.


Electric Drive

Like the hydraulic drive above, using electric power generated by the engine is another way of producing air power. While the availability of sufficient power to produce large air volumes is unlikely, small electric driven compressors can be used when air flow and duty cycle are very low. As electric vehicle technology continues to evolve, it’s likely that more powerful electric driven air compressors will emerge on the market.



Choosing a drive method for your compressor comes down to your unique situation, air compressor requirements, and equipment available to you. Some methods are more straightforward than others, but each power option has its time and place. The choice of how best to drive your air compressor system is best discussed with the members of the application team of your engine distributor and your air compressor manufacturer.

The Top 7 Questions When Adding a Compressor to Your Industrial Engine

When you are looking at considering putting a compressor on a John Deere™, Kubota™, Cummins™, Caterpillar™, Deutz™, Robins-Subaru™, Isuzu™ or a multitude of other industrial engine manufacturers, there are some key questions about your engine and your application that need to be answered before you can determine the best solution.

Here are some important questions to have answered:

1. What are you using the air for?

This helps to ensure that you are choosing the most appropriate solution for your unique requirements. How many CFM (cubic feet per minute) and at what pressure do you require to run your tools or equipment correctly?

2. What duty-cycle do you require for the compressor to operate?

This refers to how much you are using the compressor in a given time frame. Do you need air continuously for a piece of machinery (100% duty cycle) or infrequently to do small jobs? (say 15 minutes at various intervals over an hour – 25% duty cycle). This is critical information for selecting the type of air compressor solution you should be pursuing. Is it a heavy duty application where a robust solution like a rotary screw air compressor would be best, or is it a light duty application that an inexpensive reciprocating air compressor is going to provide better value? How critical is the air requirement? How much will downtime cost you?

3. What is your engine load?

Do you require air while running another piece of equipment from the same engine? If multiple pieces of equipment are running at the same time, the power being drawn from the engine is greater than if you turn off each component when not being used. How much horsepower are you already using for your equipment and how much will be available to power the compressor? Not only does this information help calculate the power requirements but also acts as a guide to the type and complexity of control system needed. It is important to ask, “what is really required?” instead of, “what would be nice to have?”.

4. What air pressure do you require?

This also helps to determine the power requirements for the compressor. It potentially determines what type of compressor will be required. High pressure applications require specialized compressors. It is important to not over specify your needs as that may increase costs, create less reliable systems and potentially shorten tool and equipment life downstream of the compressor.


5. What environment do you operate in?

This information is really important for you to know in order to correctly specify cooling and filtration requirements. If you work in frigid conditions, you will also need to consider ways of ensuring the compressor will work well in the cold. Extreme heat requires more cooling. Do you work in dusty environments? If so, protecting your compressor from dirt and other debris will improve the longevity of your compressor. Understanding how the engine and equipment behaves while operating is also a requirement. Is it stationary, moving or rocking back and forth?

6. What is your engine and equipment mounted to?

Are you mounting your equipment to a stationary skid or trailer? Is it truck mounted or on an auxiliary piece of equipment attached to the truck? Are you limited by the space around the unit or is there a requirement for the equipment to be within the confines of an enclosure? Oftentimes, compressors must be mounted to an existing piece of equipment that already has a frame and a sheet metal enclosure, without making changes to the existing structure. Vibration also has to be addressed if your equipment operates in a high vibration environment.

7. What engine are you using?

Can you make changes to your engine if needed?There are many options available from the engine manufacturer for each engine and some are extremely important to the mounting of an air compressor. Engine mounts, coolers, water pump options, auxiliary ports, alternator size, front cover, harmonic balancer and pulley are a few things to consider. What is the horsepower of the engine? Is an auxiliary port available, if so, what type is it? How much free space is around the engine? How about the radiator; is there extra cooling capacity available to handle the heat load from the compressor or will you need to either increase its size or add additional cooling capacity?

Along with the engine details, you need to know what speed your engine is running at. What is the typical operating RPM (revolutions per minute)? The minimum and maximum RPM information is also important. If you want a belt driven, clutch actuated compressor solution, you will need to know at what engine RPM the clutch will be engaged. If the speeds are too high, there is a risk of the clutch burning out prematurely; a control system would be required to prevent this from occurring. Compressor safety systems can also be programmed in to prevent occurrences like over temperature conditions.


There is nobody that knows your business, environment and equipment better than you. With your knowledge and answers to these questions, you are well on the way to adding a compressor to your piece of equipment.

Lastly, it is important to find an air compressor provider that will work with you, and provide the support and expertise that you need. A compressor can be purchased from anyone, but are they asking these questions up front, or just trying to sell you a compressor and leaving you high and dry when it doesn’t meet your expectations, or leaves your operator with an expensive breakdown in the field? Do your research to ensure you get the results you require.

If you need help answering these questions, please don’t hesitate to contact us.