Easy Guide To Rotary Screw Air Compressors (2020 Edition)

G30 Gas Driven Air Compressor

G30 Gas Driven Air Compressor

Updated: Jan 9, 2020.

Rotary screw air compressors operate by trapping air between two meshed rotors and reducing the volume of that trapped air as it moves down through the rotors. This reduction in volume results in compressed air, which can then be used to power air tools, inflate tires, or in numerous other applications.

In this guide to rotary screw air compressors, we tell you everything you need to know, including:

Intro to Rotary Screw Air Compressor?
Oil-Injected vs. Oil-Free Rotary Screws
Air Compressor Components
Basic Functions & Operation
Power Sources For Mobile Air Compressors
CFM & PSI
Advantages of Rotary Screw Air Compressors
Disadvantages of Rotary Screw Air Compressors
Types of Rotary Screw Air Compressors
Manufacturing Rotary Screw Air Compressors

Intro to Rotary Screw Air Compressor?

When most people think of air compressors, they picture reciprocating air compressors (also known as piston air compressors.) These air compressors physically push air into a small space, using pistons, and then collect that compressed air in an air receiver tank. Reciprocating air compressors are relatively inexpensive and have been around for decades.

Rotary screw air compressors are a newer, improved type of air compressor. They are more expensive than traditional reciprocating models but have numerous benefits that are quickly making rotary screw air compressors the system of choice for service truck and van fleet managers around the world.

Rotary screw air compressors operate by trapping air between two meshed rotors and reducing the volume of that trapped air as it moves down through the rotors. This reduction in volume results in compressed air, which can then be used to power air tools, inflate tires, or in numerous other applications.

You can learn more about rotary screw versus other types of air compressors in these articles:

Oil-Injected vs. Oil-Free Rotary Screws

Rotary screw air compressors used on trucks and vans are oil-injected, which means oil is used to lubricate and seal the rotors in the air end. This allows the rotors to create high pressures quite quickly and compress air in a single stage. The oil then gets separated out from the air before the air exits the system and is recycled back into the air end for reuse. Oil-injected rotary screws allow the compressor systems to provide high CFM and psi on a continuous basis.

Oil-free rotary screw models are used in industrial, production or medical applications when absolutely no oil can enter the airflow, like for food packaging or medical oxygen. Oil-free rotary air compressors are more expensive, as they require 2 stages of compression to reach the same pressures of an oil-injected rotary system. Most companies only use oil-free rotary screw air compressors when they absolutely need to so oil-free air compressors aren’t usually found on vehicles.

This guide is dedicated to rotary screw air compressors used on vehicles and therefore focuses on oil-injected rotary screws by default.

Air Compressor Components

Air-ends

Many components make up an air compressor, but the heart of the system is the “air end.” The air end is the part of a rotary screw air compressor system in which the air is compressed. An oil-injected air end looks like this:

Air enters the air end through an inlet valve, where it is mixed with oil while being compressed. The oil is then separated from the air, which exits the system. Learn more about how the air compressor system works in the Basic Functions & Operations section below.

While the air end is where air compression actually happens, there are many additional components required to make a rotary screw air compressor work.

Other Common Components

air filter

Air filter

Air filter

The quality of air entering your compressor will affect the longevity of your system. Using an air filter suited for the environment and the air flow required is a necessity.

That air filter can either be mounted directly to the compressor or remotely mounted and connected with an air intake hose. Cool, clean air should be considered when choosing the location of the filter.

Primary Separator Tank

Primary separation filter

Primary separation filter

When compressed air leaves the air end it is mixed with compressor oil. This mixture enters a primary separator tank where the first steps in separating the oil from the air happens. The primary separator tank uses mechanical separation and centrifugal force to drive oil molecules together, which form droplets that eventually fall to the bottom of the tank. A large amount of oil is removed from the air in this stage. Often, the separator tank also acts as an oil reservoir.

Secondary Separation Filter

Secondary separation filter

Secondary separation filter

Once the compressed air leaves the primary separation tank it is close to being oil free. The remaining oil mist mixed with the air will enter the secondary separation filter, which is a coalescing filter. This filter includes a membrane material that gathers the remaining oil particles and circulates the oil back into the main oiling system. The air leaving the coalescing filter is considered oil free.

The secondary separation filter can be attached to the primary separation tank or mounted remotely on its own filter manifold. Figure 5 above includes both the primary separation filter (labelled Stage 1) and the secondary separation filter (Stage 2).

Oil filter

Oil filter

Oil filter

As a rotary screw compressor has a closed loop oiling system, the installation must include an oil filter. The oil filter’s job is to collect any loose particles that have collected in the oil and shouldn’t re-enter the air compressor system. The oil filter can be located on the compressor, the separator tank or mounted remotely on a filter manifold.

Oil Cooler

Oil cooler

Oil cooler

The process of compressing air generates heat—and lots of it! This heat warms up the oil, which must pass through a cooler before it is circulated back to the compressor. A liquid to liquid cooler can be used in conjunction with an engine’s cooling system or a stand-alone air to liquid cooler can be used; each has its own benefits.

The liquid to liquid version will need sufficient cooling capacity to cool the compressor oil combined with the engine cooling. The air to liquid cooler will need clean, cool air to keep the oil within an optimal temperature range.

Air compressor hose

Air compressor hose

Hoses

Moving oil and air between various air compressor components requires the use of hoses. The hoses must meet the requirements of heat, pressure and the chemical components of the compressor oil. Incorrect hose selection will result in premature failure of those hoses, which can be expensive and dangerous.

VMAC hydraulic system control

VMAC hydraulic system control

Controls

Air compressors will use mechanical or electrical controls in the form of a button, switch, or lever. These controls will turn the air compressor off and on and may also provide important diagnostic or service information. The location and type of components used in the controls should reflect the environment the air compressor will be in.

Oil

High performance synthetic oil

High-performance synthetic oil

Oil is a critical component of an oil-injected rotary screw air compressor, performing many important jobs at once. Oil lubricates the system, protects components from wear, keeps the system cool, and helps trap and remove contaminants. Without the right type of synthetic oil, oil-injected rotary screw air compressors would not function.

The components listed above are necessary, in some form, for a rotary screw air compressor system. There are many more options for filter manifolds, coolers, oil separators, and so forth. Each system is a bit different, which means the required components are as well.

Encapsulated Air Ends

Encapsulated air end

Encapsulated air end

Some manufacturers use encapsulated air ends, which combine several components within the air end’s metal casing, including the rotors, intake valves, and separators in a seemingly convenient package. However, encapsulated air ends are bulky and restrictive, which can present design challenges for air compressor manufacturers, vehicle upfitters, and OEMs. The combined pieces result in an awkward, inflexible shape that must be accommodated.

When manufacturers choose not to combine multiple components within an encapsulated air end, they have the freedom to design smaller systems with more efficient designs, without compromising on power or efficacy.

Basic Functions & Operation

Rotary screw air compressors are pressurized systems, comprised of many interconnected components that work together to compress air.

Air and oil are both important aspects of a rotary screw air compressor system. Compressed air is the end goal, which requires the use of atmospheric air, but the oil is just as important. Oil is used to lubricate the system and is the not-so-secret weapon that makes rotary screws so efficient at a lower price-point.

But the use of oil also makes the air compressor systems more complex. In addition to requiring a mechanism for producing compressed air, rotary screw air compressors also need to circulate, filter, and recycle oil.

In a sense, there are two separate systems working together: one makes air and the other circulates oil. Combined, the systems look something like this:

Air compressor system flow

A step-by-step guide to the system flow can help explain how the air and oil processes flow together within a single cohesive system:

System Flow Process

Step 1: Atmospheric air enters the inlet valve.
Step 2: Air flows through the system pressure line to a valve on the regulator, which sets the pressure for the entire system.
Step 3: Air is mixed with oil and compressed via the rotors in the air end.
Step 4: Air mixed with oil exits the air end via the air discharge hose.
Step 5: Air mixed with oil enters the primary oil separator tank, which separates most of the oil from the air.
Step 6: Air enters the second separation filters, which catches remaining oil mist in the air.
Step 7 – A: Oil-free air exists the system; if an air receiver tank is used, the air collects in the tank.
Step 7 – B: Oil is moved into the oil cooler, cooled down, and then sent to an oil filter.
Step 8: The oil filter catches any debris remaining in the oil.
Step 9: The recycled oil is returned to the air end, via the scavenge line.

Note that visualizing the process as steps makes it easier to understand the overall flow, but these steps operate concurrently. As soon as the air compressor is turned on, all the steps outlined above occur simultaneously and continuously.

Power Sources For Mobile Air Compressors

Air compressors need a power source to run. Fortunately, vehicle mounted air compressors have several options: a separate air compressor engine, using a truck or van’s existing engine, or tapping into an auxiliary power source like a PTO or hydraulic port.

For example, here is a breakdown of VMAC’s rotary screw air compressors and their power sources:

VMAC Air Compressor/Multi-Power System Power Source
G30 Gas Driven Standalone Gas Engine
D60 Diesel Driven Standalone Diesel Engine
Multifunction 6 in 1 Standalone Diesel Engine
H40/H60 Hydraulic Driven Hydraulic Port
Direct-Transmission Mounted™ PTO
UNDERHOOD™ Gas or Diesel Vehicle Engine

 

In summary, there are a lot of power options for mobile air compressors. The right one depends on a vehicle’s existing power options and whether they will work with an air compressor that provides enough CFM and psi. Vehicle engine mounted and hydraulic air compressors are convenient, while standalone engines are efficient and cost-effective.

CFM & PSI

Air power is typically measured in CFM and psi. CFM or “Cubic Feet per Minute”, is the amount of air that’s being delivered. Meanwhile, psi or “Pounds per Square Inch” is the amount of force behind that air. Together, CFM and psi determine how much air is being delivered and at what pressure. Air tools require the right psi and the right CFM to operate efficiently.

Rotary screw air compressors tend to produce lower psi than reciprocating air compressors, but this isn’t a problem for most mobile air applications. Most air tools run at 80 to 110 psi, which is well within the capabilities of rotary screw air compressors.

Find out more about CFM and psi in these two articles:

Advantages of Rotary Screw Air Compressors

Rotary screw air compressors have many benefits that make them ideal for both mobile and standalone applications. As a result, you’ll find rotary screw air compressors on vehicles and trailers, as well as in industrial, production and medical facilities, where high quality equipment is required.

The benefits of rotary screw air compressors over other compressor types include:

  • Continuous airflow/100% duty cycle
  • Larger quantities of air
  • Higher CFM per hp
  • Longer lifespan
  • Better warranties
  • Quieter
  • Energy efficient

Most people appreciate the longevity, reliability, and easy access to instant air. Because rotary screw air compressors can run continuously, there’s no need to wait for an air receiver tank to fill before you can start using the air. Those tend to be the most popular benefits of rotary screw air compressors.

Many operators also appreciate the limited lifetime warranties that come with some rotary screw air compressors, like VMAC’s. These types of warranties are available because the rotors and air ends are proven to stand the test of time—or, more specifically, the life of a modern service truck. This longevity makes rotary screw compressors a drama-free option.

For example, the very first VMAC rotary screw air end outlived the truck it was installed on. The rotors were returned to us and now have a permanent home in our trophy case.

VMAC's first rotors

VMAC’s first rotors, which outlived the truck

Rotary screw air compressors’ lengthy lifespan is a huge advantage over reciprocating air compressors, which are jokingly referred to as “throw-away air compressors” because they’re expected to fail after 3 to 5 years.

Disadvantages of Rotary Screw Air Compressors

Rotary screw air compressors have a lot of advantages, but they aren’t the right choice for everyone. Common rotary screw air compressor disadvantages are:

  • Upfront cost
  • Skilled maintenance required

The number one reason people choose a reciprocating air compressor over a rotary screw is the initial cost. Rotary screw air compressors often cost twice as much as reciprocating air compressors, but it’s a situation where you genuinely get what you pay for.

Rotary screw air compressors may be 2x the cost, but they last at least 4x longer, on average, and produce more air. That makes them a solid investment for any business that plans to use compressed air over the long term.

The other disadvantage to rotary screw air compressors is that they require skilled maintenance. Every type of air compressor needs regular servicing, but rotary screw systems require a higher level of expertise due to their complex nature. Fortunately, detailed manuals and manufacturer tech support team can help alleviate any inconvenience.

Types of Rotary Screw Air Compressors

There are many types of rotary screw air compressors used on vehicles in mobile applications. VMAC’s air compressor systems demonstrate the range of rotary screw compressor options for vehicles:

UNDERHOOD™ Air Compressors

UNDERHOOD™ air compressor systems are one of the coolest options out there, as the air compressor components are integrated with existing truck or van components. The air end is mounted within the engine compartment and the compressor system is powered by the vehicle’s existing engine. UNDERHOOD air compressors are super light, weighing in at 62 to 200 lbs (depending on the system), which saves precious GVW and their integrated location frees up cargo space.

Installed UNDERHOOD air compressor

Installed UNDERHOOD™ air compressor

DTM70

DTM on 3D-printed Transmission Model

Direct-Transmission™ Mounted Air Compressors & Multi-Power Systems (DTM)

The Direct-Transmission Mounted air compressor uses a vehicle’s PTO to drive the air compressor. Like the UNDERHOOD, the DTM is a lightweight “out of sight” option that integrates with a vehicle’s existing components.

G30 Gas Driven Air Compressor

G30 Gas Driven Air Compressor

Gas Driven Air Compressor (G30)

The G30 gas driven air compressor has a separate Honda GX390 gas engine, like you’d find in a ride-on lawn mower or other small vehicles. This style of air compressor is mounted to a truck or van and can be easily accessed by any operator with a key.

Diesel Driven Air Compressor (D60)

Similar to the G30, VMAC’s D60 is a diesel driven air compressor with its own Kubota diesel engine. These air compressors are also easily mounted to a work vehicle.

D60 Diesel Driven Air Compressor

D60 Diesel Driven Air Compressor

VMAC Hydraulic Air Compressor

VMAC Hydraulic Air Compressor

Hydraulic Driven Air Compressor (H40, H60)

Vehicles that have existing hydraulic systems can tap into those systems to power their air compressor. The VMAC hydraulic driven air compressor makes sense for operators with hydraulic cranes and other hydraulic-powered equipment.

Multifunction Power Systems

Multipower or multifunction systems are a popular option now being offered by some manufacturers. Multipower systems combine air compressors with other vehicle-mounted equipment, such as welders, generators, and boosters, in one convenient system. VMAC’s Multifunction Power systems are powered by a Kubota diesel engine.

MF-CAT Air Compressor

VMAC Multifunction with Cat® engine

Manufacturing Rotary Screw Air Compressors

Rotary screw air compressors are made up of numerous parts that need to be assembled into a highly efficient system. True air compressor manufacturers will create these parts within their facilities, using an in-house foundry, CNC machines, and other specialized equipment to make the required components. Individual components are then assembled on-site into an air compressor system.

Crucible & furnace in VMAC's foundry

Crucible & furnace in VMAC’s foundry

One of VMAC's CNC machines

One of VMAC’s CNC machines

VMAC’s coordinate measuring machine

Design Tolerances

When engineering and manufacturing parts for any system or machine, there is an acceptable margin of error, called tolerance.

The required dimensions for air ends in rotary air compressor systems are so precise that these tolerances are incredibly low. Computer Numerical Control machines—CNC machines, for short—allow manufacturers to meet the exact tolerances needed for rotary screw air compressors.

For example, these are the maximum tolerances VMAC allows for parts made with CNC machines in comparison to the parts made using manual machines:

  Maximum Tolerance Suggested Tolerance
CNC Mills ±0.0003 ±0.005
CNC Lathes ±0.0003 ±0.005
Manual Mills ±0.001 ±0.005
Manual Lathes ±0.001 ±0.005

A stringent quality control process ensures the required tolerances for each machine are met. If a machine fails to produce parts within the acceptable tolerance, those parts are melted back down or otherwise recycled. In that scenario, the designs and machines will also be evaluated and adjusted, as needed.

Fortunately, manufacturers using modern quality control technology can usually predict when a CNC machine will need to be adjusted well in advance, and plan for that maintenance accordingly.

True Manufacturers vs. Assembly Companies

One major advantage to making parts on-site is that the parts can be modified at will. Instead of being restricted by existing component shapes and sizes, true manufacturers have the freedom to innovate on individual parts on their own desired schedule, creating more efficient, powerful and compact air compressor systems.

A more common type of air compressor manufacturer will purchase existing parts from suppliers or, less often, contract their creation out to external companies. If a custom part is required, these air compressor companies have to book a space with third-party foundries, machinists, and other specialists, and then rely on their general expertise for modifications. This style of air compressor manufacturer essentially assembles pre-purchased pieces into air compressors before shipping them out to customers.

VMAC is one of the only true rotary screw air compressor manufacturers in North America.

9 Reasons You Should Ditch Your Tow-Behind Air Compressor

Tow-behind air compressors took the world by storm a few decades ago when they met a simple need: available compressed air, wherever you want it. It was a game-changer for a lot of industries.

But once the novelty of tow-behind air compressors wore off, their limitations became apparent. Manufacturers began to look at innovative ways to solve these problems and, in the 1980’s, companies began to invent new air compressors that would revolutionize mobile air once again.

Today, workers who need compressed air have a medley of compressor options, many of which make more sense than a tow-behind. Let’s talk about 9 reasons you may want to ditch your tow-behind air compressor:

9. Enjoy hassle-free driving and parking

If you have a tow-behind air compressor, chances are you’ve become a bit of a pro at dragging your trailer through busy freeways, reversing without jack-knifing, and circling job site lots until you find a suitable parking spot. This might even seem normal to you. But there’s a better way!

When you ditch your tow-behind air compressor and switch to a vehicle mounted air compressor instead, you’ll feel liberated. You’ll suddenly have more freedom! Driving, reversing, and parking all become second nature again, and you won’t be restricted by your trailer’s capabilities or driving expertise.

If you’re a business owner, you’ll have peace of mind knowing your staff aren’t trying to negotiate your expensive equipment in heavy traffic, park in precarious situations, or backup in environments where space can be highly limited.

Speaking of which…

8. Improve your access to job sites

Dropping your tow-behind can also improve your access to important job sites, as tow-behind compressors are clunky and can limit your work opportunities. A lot of mobile service work is in remote or off-road areas, requiring vehicles that can navigate the challenging terrain. Trailers don’t tend to do well in tricky environments, requiring additional time and care to get to the work site—if accessible at all.

7. Free up your hitch for other equipment

Tow-behind compressors take up a seriously underrated asset on your vehicle: the tow hitch! Many workers have equipment that can only be transported by a hitch, while others simply prefer to tow a trailer with their tools. If your air compressor is taking up that spot on the hitch, you’ll need to make other compromises to get your equipment where it needs to be.

In some cases, business owners send out an extra vehicle and driver just to get all the right equipment in one spot. In others, favorite pieces of equipment are left behind or require extra trips to retrieve. When you mount your air compressor to the truck itself, you free up your hitch and improve your productivity.

One fantastic example of this improved productivity is with asphalt crack sealing, where cracks need to be blown out before they can be sealed. A truck-mounted air compressor can be used to blow the dirt out of the cracks, as the hitch pulls the asphalt applicator immediately behind.

6. Have an air compressor that’s always with you

Imagine this: you’ve just arrived at your next job only to realize it needs the air compressor you left behind. You have to actively plan for every trip with your tow-behind compressor, and decide whether it’s worth bringing along. What a hassle!

Alternative mobile air compressor systems have the compressor mounted to the truck itself, which means it goes everywhere the truck goes. If you need air, it’s there. You’ll never have to experience the frustration of needing the air compressor that’s halfway across town.

5. Need fewer safety checks & measures

You probably already know that there’s more than just physical baggage with a tow-behind, and they carry the need for extra safety precautions everywhere they go. The hitch, taillights, and tires all need to be checked frequently and, if any of these parts are failing, you’re not going anywhere until they’re fixed.

In addition, tow-behind air compressors make it harder for vehicles to stop quickly and safely. That means you need to reduce your speed whenever you’re towing your compressor, wasting valuable time that could be spent on the job or with your family. Throw in tow bar regulations, a larger blind spot, and the need to monitor the compressor itself, and you’ve got a lot of extra safety checks in your day.

And let’s not forget about thieves. Tow-behind compressors are often targeted by thieves because the units can be stolen in just a few minutes. By contrast, compressors that are mounted directly to a vehicle are significantly harder to take, while UNDERHOOD air compressor systems are practically impossible to steal.

When you stop towing your air and upgrade to a mounted air compressor, a lot of these safety concerns are instantly eliminated. Your compressor becomes a part of your truck or van, requiring fewer checks and precautions, and driving becomes safer.

UNDERHOOD air compressors banner

4. Less engine maintenance

Tow-behind air compressors require their own engine, in addition to the engine that’s included in the vehicle that’s doing the towing. That means two engines need to be maintained for every tow-behind compressor. This maintenance takes up valuable time and money that could be used elsewhere.

While some mobile air compressors require their own engine, many don’t. Recent air compressor innovation has been highly focused on utilizing existing energy sources to power mobile air compressors. For example, gas and diesel vehicle engines, transmissions, and PTOs that run hydraulics can all be used to power an air compressor.

3. Finish your jobs fasters

Time is money. The faster you finish your work, the more time you have to wrap up your “to do” list, take on more jobs, or even just enjoy an extra long break or two. Tow-behind compressors take time to properly position, set up and use.

When you upgrade a tow-behind to an UNDERHOOD, underdeck or abovedeck mobile compressor, you’ll be amazed at how quick and easy it is to get a job done. In some cases, the prep is as fast as flipping the “on” switch and grabbing the tool, while the job itself can be just as quick.

If you’d like more time in your day (and who wouldn’t), it might be time to give your tow-behind the boot.

2. Enjoy fuel & weight savings

Tow-behind air compressors are beasts. They’re notorious for being overweight monsters and they got that reputation for a reason… The Atlas Copco XAS 110 is a relatively small tow-behind compressor that can produce 110 CFM and weighs in at 1100 lbs. By contrast, the UNDERHOOD 150 air compressor provides similar air power and weighs about 200 lbs. That’s a huge difference! Choosing a lightweight air compressor means you’ll be able to add more tools and equipment to your truck, carry more materials, or take advantage of better fuel economy.

1. Discover more innovative alternatives

One of the best reasons to ditch a tow-behind air compressor is because there are much better options out there! Tow-behinds have the luxury of being overweight space-hogs, while other compressor styles have continually adapted to market demands with fresh innovations. For example, vehicle-mounted compressors can deliver more than enough air for light to medium duty applications, and do so in a system that’s significantly smaller, lighter and more compact than a tow-behind.

With modern compressor technology, you can enjoy all the benefits of having mobile air, while also freeing up cargo space, reducing gross vehicle weight, and working more efficiently. These benefits are why you’ll see onboard air compressors mounted to the vehicles of hard-working people like construction workers, military personnel, public works and utility workers, and fleet managers.

Vehicle mounted compressors are the smart choice for people who:

  • Need mobile air regularly
  • Have light/medium-duty applications, such as
    • Post pounding
    • Pressurizing gas lines
    • Road repair & crack sealing
    • Pavement breaking
    • Sandblasting
    • Sprinkler irrigation
    • Fiber optic cable shooting
    • Utility servicing
  • Want more space for cargo or other equipment
  • Prefer less weight and strain on their vehicles
  • Have the budget to make a long-term investment

At the end of the day, you deserve equipment that helps you get your job done quickly, easily, and safely. Tow-behind air compressors are necessary for some types of work, but there are a lot of downsides that you may have to endure. If you have the option to upgrade to a modern mobile air solution, then it’s time to ditch your tow-behind air compressor!

View this post as a shareable infographic here!

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Top 3 Challenges Caused By Over-Weight Heavy Duty Pickup Trucks

Gross vehicle weight ratings (GVWR) and payloads can differ from vehicle to vehicle and it’s important to know what you’re working with when specifying or upfitting a specific heavy duty pickup truck. Before we get into the details on why it’s important to pay attention to vehicle weight ratings, let’s go over some important concepts: GVWR and Payload.

Continue reading “Top 3 Challenges Caused By Over-Weight Heavy Duty Pickup Trucks”

How to Choose A Mobile Air Compressor For Your Work

Mobile air compressors are a beautiful thing. They make life easy by offering mobile air on demand, wherever you are, and can power high-quality pneumatic tools. But choosing a mobile air compressor can feel overwhelming, with an abundance of information and decisions to consider.

Fortunately, we’re going to make it easy for you to narrow down your options. In this blog, we’ll talk about the simple steps you should follow to choose the best mobile air compressor for the jobs you do.

1: Determine your CFM and PSI requirements

The very first thing you should do is determine your air needs. Pneumatic tools all require different amounts of air and these needs vary quite a bit, even within a single type of tool, which is why you should find out what your tools need as your first step.

Air power is typically measured in two metrics: CFM and PSI. CFM or “Cubic Feet per Minute”, is the amount of air that’s being delivered. PSI or “Pounds per Square Inch” is the amount of force behind that air.

Most tools are rated to run optimally at 80 to 110 PSI, so you’ll want to find an air compressor that can deliver the right CFM at the PSI your tools require. The best way to determine your PSI and CFM requirements is to review all the tools you will be using and check with the manual or manufacturer. If you plan to use more than one air tool at the exact same time, you’ll need to add the CFM requirements of each tool together to determine your total CFM requirements.

For now, you can get a general idea of your CFM requirements here.

2: Decide on a Rotary or Reciprocating Air Compressor

The next step is to determine what type of compressor you need. VMAC exclusively manufactures rotary screw air compressors because they last significantly longer, are a higher quality, can provide air instantly while maintaining constant air flow, and are smaller and lighter. But let’s take a quick look at the pros and cons of both types of air compressors:

Rotary Screw Pros:

  • Continuous airflow / 100% duty cycle
  • Longer lifespan
  • Larger quantities of air
  • Higher CFM per hp
  • Quieter
  • Smaller
  • Lighter

Rotary Screw Cons:

  • More expensive up front
  • Requires skilled maintenance

Reciprocating Pros:

  • Capable of high pressures
  • Less expensive
  • Easier maintenance

Reciprocating Cons:

  • Interrupted flow rates
  • Low life expectancy
  • Maintenance costs
  • Excessive heat
  • Louder
  • Heavy
  • Bulky
In a nutshell, if you’re looking for a cheap way to get your jobs done for the next year or two, a reciprocating air compressor is probably the way to go. But if you need reliable mobile air for the next 5 to 10 years and are willing to pay more for a better-quality solution, rotary screw air compressors are your best bet.

You can read more about reciprocating air compressors versus rotary screw air compressors in this blog.

3: Consider Tow-Behind or Vehicle-mounted

Now it’s time to think about how you want to move your air compressor around. There are two major contenders that you can consider:

  • Tow-Behind Air Compressors
  • Vehicle-mounted Air Compressors

Tow-behind air compressors are air compressors that are mounted onto a trailer and towed by the hitch of your vehicle. They’re not our favorite option and we outline the reasons why don’t love tow-behind air compressors in this blog. However, if you need high CFMs, plan to leave your air compressor in the same spot for weeks or months at a time, or you simply love towing things around, a tow-behind air compressor may be worth considering.

Otherwise, you’re looking at vehicle-mounted air compressors as your best bet. There are two common ways that air compressors are mounted to a vehicle:

1. The simplest way to mount an air compressor is to simply attach a compressor with its own diesel or gas engine onto the back of a truck (or in a van’s cargo hold). Here’s a photo from TiNik Inc. that shows off this style perfectly:

TiNik-Inc-Service-Truck

Mounting air compressors in this way is relatively easy and inexpensive, which is why a lot of operators love this style.

2. The other way to mount an air compressor is to intertwine the air compressor components with a vehicle’s existing components. These installs are sophisticated and most people can’t even see the air compressor because it’s tucked away in the engine compartment. Take a look:

VMAC-Underhood-Air-Compressor

Engineers at companies like VMAC work with vehicle manufacturers to determine the best way to install these air compressors, ensuring the vehicle warranties are always still in effect. However, whether an air compressor can be mounted in this manner depends on the specific vehicle. You can see if your vehicle is compatible here!

4: Determine Your Power Source

Air compressors can be powered by many different sources. If you’ve decided on a tow-behind air compressor, you’ll be limited to gas or diesel engines. In this case, it makes sense to just go with an air compressor that uses whatever type of fuel your vehicle already takes, for simplicity.

But if you’re going ahead with a vehicle-mounted mobile air compressor, you have options! Some air compressors have their own gas or diesel engines, while others can integrate into a truck’s existing engine or hydraulics. Air compressors that mount under the hood use these existing systems, which makes them convenient.

As one example, here are the product lines that VMAC offers for various power sources:

VMAC Systems table

Consider what type of power sources you already have available and think about whether they will work for your air compressor. Using your vehicle’s engine or existing hydraulics can be a highly convenient way to power an air compressor. However, if that doesn’t work for you or your vehicle isn’t compatible, air compressors with their own gas engine or diesel engine can be just as effective in getting the job done.

5: Find An Upfitter That Knows Air Compressors

By this point, you should have an idea of what you’re looking for in an air compressor and be able to answer some simple questions. Let’s break them down:

  • How much CFM do you need?
  • Rotary screw or reciprocating?
  • Tow-behind or vehicle-mounted?
  • What is the power source?

Now you’re ready to talk about specific brands and options. If you’ve decided to go ahead with a vehicle-mounted rotary screw air compressor, your next step will be to find an upfitter. The upfitter will be able to share the specific options available to your vehicle and provide you with quotes for purchasing and installing the air compressor. Check out our Dealer Locator to see our favorite upfitters!

If you’d rather have a reciprocating compressor or a tow-behind air compressor, there are numerous options available. Again, we recommend working with an upfitter who knows air compressors well and can help you choose the best compressor for your individual needs.

Curious what other operators are using? Find out in these posts:

Fanelli Equipment Repair Upgrades to VMAC DTM70-H

Located in Hilmar, CA is Fanelli Equipment Repair. Owned by Phil Fanelli, this company has been operating in the Central Valley area for over 12 years, repairing and servicing all types of Caterpillar equipment, including landfill, recycling, and compost equipment for waste management companies, as well as servicing equipment used in the dairy industry.

Phil Fanelli has successfully grown his equipment repair business to include seven service trucks, each which puts on thousands of operating hours and up to 50,000 miles every year. “I work my trucks hard, and so I rotate through them every five years, to ensure there’s no downtime,” says Fanelli. “Because of this, I expect any piece of equipment to last me five years as well.”

Up until recently, Phil’s service truck was equipped with a reciprocating air compressor. This reciprocating air compressor resulted in a lot of challenges, the first and foremost being weight. The compressor was terribly heavy on his truck, which at the time was a Peterbilt with a 14-foot service body. Phil also found himself waiting for compressed air to be produced, resulting in downtime as his compressor tried to catch up to him. This slowed down his work.

When it was time to bring in a new service truck to the fleet, Phil seized the opportunity to “right-size” his truck. Because he’s often travelling to visit his technicians on different job sites, he chose to downsize to a Ford F550 truck. He also needed to address the weight and air supply concerns associated with reciprocating compressors. For this truck build and upfit, he went straight to Spencer Hinson, owner and GM of Lodi Truck and Equipment, located in West Sacramento.

“I’ve been getting Spencer at Lodi to build my trucks for over 10 years now, and I wouldn’t go anywhere else,” says Phil. “I go in, tell him what I want, and he keeps me involved in every step of the build.”

At first, Phil was interested in an UNDERHOOD™ 70 air compressor, which fits neatly in the engine compartment of the truck, supplies up to 70 CFM of air continuously, and weighs just 150 lbs, saving up to 260 lbs. But when it was time to start the truck build, Spencer recommended a different product: the newly released VMAC DTM70-H, a direct-transmission mounted PTO driven air compressor with hydraulic pump. The DTM70-H is the best choice for customers like Phil who are concerned with saving weight on their service truck, and who also need compressed air and hydraulic power at the same time.

“Spencer knows I’m really concerned about weight. It seems like I’m always overloaded, and he thought this set up would be the best fit,” explains Fanelli. And the weight savings were significant: “The VMAC DTM70-H saved 500 lbs, which is a big deal when you’re trying to set up an F550. With these weight savings, it was the only way to go. We were looking at aluminum doors and aluminum fuel tanks, but to save 500 lbs with one change tFinelli-VMACo the DTM70-H was a no-brainer.”

The VMAC DTM70-H weighs only 180 lbs, which frees up hundreds of pounds of weight, and allows customers like Phil to downsize their trucks, and at the same time load the truck up with more supplies. “I added more tools, a drawer set, tool boxes, and an oil tank, thanks to the weight savings,” says Fanelli.

It’s been several months since Phil picked up his new F550 truck from Lodi, and he’s been using the DTM70-H to power his air tools and crane simultaneously. Spencer’s expertise and recommendation was key in this new truck build and was exactly what Phil needed. “When I got the truck, it was show room quality, detailed, everything worked. It was exactly the way I wanted it.” And as for the DTM70-H? “It’s lightweight, which is what I needed, but it also produces the air I need, when I need it. It’s bulletproof.”

Subscribe to the VMAC blog to continue reading about Fanelli Equipment Repair’s experience with the VMAC DTM70-H, and to learn more about Lodi Truck & Equipment, located in West Sacramento, CA.

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