EASY Gas Powered Air Compressors and Air Compressor-Generators User Guide
- June 13, 2024
- EASY
Table of Contents
- Intro to Rotary Screw Air Compressors
- Oil-Injected vs. Oil-Free Rotary Screws
- Air Compressor Components
- Other Common Components
- Encapsulated Air Ends
- 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
- References
- Read User Manual Online (PDF format)
- Download This Manual (PDF format)
EASY GUIDE TO ROTARY SCREW
AIR COMPRESSORS
User Guide
Intro to Rotary Screw Air Compressors
When most people think of air compressors, they picture reciprocating air
compressors, also known as piston air compressors. These air compressors use
pistons to push air into a smaller space, compressing it, and then that
compressed air is collected in an air receiver tank.
Reciprocating air compressors are relatively inexpensive and have been around
for decades. ![EASY Gas Powered Air Compressors and Air Compressor Generators
- Air Compressors](https://manuals.plus/wp-content/uploads/2023/10/EASY-Gas- Powered-Air-Compressors-and-Air-Compressor-Generators-Air-Compressors.jpg)
Rotary screw air compressors are a newer, improved type of air compressor.
They can be more expensive than traditional reciprocating models but have
numerous benefits that make rotary screw
air compressors the system of choice for service truck and van fleet managers
worldwide.
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, and more.
You can learn more about rotary screw versus other types of air compressors in
these articles:
- Types of Air Compressors For Your Industrial Engine
- Performance Differences of Rotary Screw vs. Reciprocating Air Compressors
- Reciprocating Engine Driven Air Compressor or A Rotary Screw Engine Driven Air Compressor?
Oil-Injected vs. Oil-Free Rotary Screws
Rotary screw air compressors used on trucks and vans are oil-injected, which means oil lubricates and seals the rotors in the air end. This lubrication allows the rotors to create high pressures quite quickly and compress air in a single stage. The oil then gets separated 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 continuously.
Oil-free rotary screw models are used in industrial, production, or medical
applications when no oil can enter the airflow, like food packaging or medical
oxygen. Oil-free rotary air compressors are more expensive, as they require
two stages of compression to reach the same pressures as 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 typically
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 comprise an air compressor, but the system’s heart is the air
end, where 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 later separated from the compressed air, before it exits the
system.
While air compression happens at the air end, many additional components are
required to make a rotary screw air compressor work. These components are
outlined below. You can also learn more about how the air compressor system
works in the Basic Functions & Operations section of this guide.
Other Common Components
Air Filter
The quality of air entering your compressor will affect the longevity of your
system, so it’s important to use an air filter suited for the environment and
the air flow.
That air filter can 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
When compressed air leaves the air end, it mixes with compressor oil. This
mixture enters a primary separator tank, where the first steps in separating
the oil from the air occur. 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 at this stage. Often, the separator tank also acts as
an oil reservoir.
Secondary Separation Filter
Compressed air is nearly oil-free once it leaves the primary separation tank.
The remaining oil mist mixed with the air will enter the secondary separation
filter, a coalescing filter.
This filter includes a membrane material that gathers the remaining oil
particles and circulates the oil back into the primary 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 filter manifold. Figure 6 includes the primary
separation filter (labeled Stage 1) and the secondary separation filter (Stage
2).
Oil Filter
A rotary screw air compressor system must include an oil filter because it has
a closed-loop oiling system. The oil filter’s job is to collect any loose
particles in the oil that shouldn’t re-enter the air compressor system. The
oil filter may be located on the compressor, the separator tank, or mounted
remotely on a filter manifold.
Oil Cooler
The process of compressing air generates heat! This heat warms up the oil,
which must pass through a cooler before it circulates back to the compressor.
A liquid-to-liquid cooler can be used in conjunction with an engine’s cooling
system, or a standalone air-to-liquid cooler can be used instead.
The liquid-to-liquid version will need sufficient cooling capacity to cool the
compressor oil and the engine. The airto-liquid cooler will need clean, cool
air to keep the oil within an optimal temperature range.
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
compressor oil’s chemical components. Incorrect hose selection will result in
premature failure of those hoses, which can be expensive and dangerous.
Controls
Air compressors will use mechanical or electrical controls like 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
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 correct type of synthetic oil, oilinjected rotary
screw air compressors would not function. The components listed above are
necessary, in some form, for a rotary screw air compressor system. Many more
options exist for filter manifolds, coolers, oil separators, etc. Each air
compressor design and its required components are a bit different.
Encapsulated Air Ends
Some manufacturers use encapsulated air ends, which combine several components
within the air end’s metal casing, such as the rotors, intake valves, and
separators, in a single package. However, encapsulated air ends are bulky and
restrictive, presenting design challenges for air compressor manufacturers,
vehicle upfitters, and OEMs. The combined pieces result in an inflexible shape
that must be accommodated.
When manufacturers choose not to combine multiple components within an
encapsulated air end, they can design smaller systems with more efficient
designs without compromising on power or efficacy.
Basic Functions & Operation
Rotary screw air compressors are pressurized systems comprising many
interconnected components that work together to compress air.
Air and oil are essential aspects of many rotary screw air compressor systems.
Compressed air is the end goal, which requires atmospheric air, but synthetic
oil is just as essential. 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.
Two separate systems work together; one makes air, and the other circulates
oil. The combined systems look something like this:
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,
separating most of the oil from the air.
Step 6: Air enters the secondary separation filter, catching the
remaining oil mist in the air.
Step 7 – A: Oil-free air exits 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 sent to an
oil filter.
Step 8: The oil filter catches any debris remaining in the oil.
Step 9: The recycled oil returns to the air end via the scavenge return
line.
Note that visualizing the process as steps makes it easier to understand the
overall flow, but these steps operate concurrently. When the air compressor is
turned on, all the above steps 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’s existing engine, or tapping into an auxiliary power source like a PTO
or hydraulic port.
For example, here’s 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 many power options for mobile air compressors. The right one depends on a truck or van’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
In North America, compressed air power is measured using CFM and psi. CFM or
“Cubic Feet per Minute” is the amount of air delivered, while psi or “Pounds
per Square Inch” is the amount of force behind that air. Together, CFM and psi
identify how much air is being delivered and at what pressure. Air tools
require the right CFM and psi 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
mobile and standalone applications. As a result, you’ll find rotary screw air
compressors on vehicles and trailers and 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 rotary screw air compressors because of their
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 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 first VMAC rotary screw air end outlived the truck it was
installed on. The rotors were returned to us and are on display in our trophy
case.
Rotary screw air compressors’ lengthy lifespan is a considerable advantage over reciprocating air compressors, which are jokingly referred to as “throw- away air compressors” because they often 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 initial cost is the primary reason people choose a reciprocating air
compressor over a rotary screw. 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 of rotary screw air compressors is they require skilled
maintenance.
Every type of air compressor needs regular servicing, but the complex nature
of rotary screw systems requires a higher level of expertise.
Types of Rotary Screw Air Compressors
Many types of rotary screw air compressors are utilized 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 integrate with the existing truck or van
components. The air end mounts in the engine compartment, and the vehicle’s
existing engine powers the compressor system. UNDERHOOD air
compressors are
super light and weigh only 62 to 200 lb, saving precious GVW and cargo space.
Direct-Transmission Mounted Air Compressors & Multi-Power Systems
(DTM)
The Direct-Transmission Mounted air
compressor uses avehicle’s PTO to drive
the air compressor. Similar to UNDERHOOD, the DTM is a lightweight “out of
sight” option that integrates with a vehicle’s existing components.
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 lawnmower or other small vehicles. This style of air
compressor mounts to a truck or van and can be used by any operator with the
key. Diesel Driven Air Compressor (D60)
VMAC’s D60 is a diesel driven air
compressor with its own Kubota diesel
engine. Similar to the G30, these straightforward air compressors are also
easily mounted to a work vehicle.
Hydraulic Driven Air Compressor (H40/H60)
Vehicles with 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
Multi-power, all-in-one, or multifunction systems are now a popular option
offered by some manufacturers. In one convenient system, multipower systems
combine air compressors with other vehicle-mounted equipment, such as welders,
generators, and boosters. VMAC’s Multifunction Power
systems are
powered by a Cat or Kubota diesel engine.
Electric Air Compressors
EV manufacturers are still racing to see who can develop the first market-
dominating electric service trucks and vans and there is no clear EV or
electric air compressor winner yet. However, as electric trucks and vans gain
popularity within the service truck industry, further development of these
technologies is inevitable; VMAC is currently field-testingelectric air
compressor technology for a range of applications.
Figure 61: VMAC Multifunction Power System
Manufacturing Rotary Screw Air Compressors
Rotary screw air compressors are comprised of numerous components assembled into a highly efficient system. Authentic 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.
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
Stringent quality control processes ensure 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. The designs
and machines will also be evaluated and adjusted as needed.
Fortunately, manufacturers using modern quality control technology can predict
when a CNC machine will need to be calibrated well in advance and plan
maintenance accordingly.
Authentic Manufacturers vs. Assembly Companies
One significant 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, genuine
manufacturers can innovate on individual parts on their 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 must
book space with third-party foundries, machinists, and so forth and then rely
on their general expertise for modifications. This style of air compressor
manufacturer assembles pre-purchased pieces into air compressors before
shipping them out to customers.
VMAC is one of North America’s only authentic rotary screw air compressor
manufacturers.
References
- Air Tool Pressure + 5 Reasons To Use The Right PSI For Air Tools | VMAC
- How Many CFM Do I Need? – Air Tool CFM Chart
- Rotary Screw vs. Reciprocating Air Compressors - Performance Comparison
- Rotary Screw vs. Reciprocating Air Compressors - Performance Comparison
- 3 Types of Air Compressors For Your Industrial Engine Application | VMAC
- Rotary Screw Air Compressors | VMAC
- PTO Air Compressors | Direct-Transmission Mounted Air Compressor
- Gas Powered Air Compressors & Air Compressor/Generators
- Hydraulic Driven Air Compressors - VMAC
- Multifunction Power Systems - VMAC Multi-Power Systems
- UNDERHOOD™ Air Compressors For Trucks & Vans - VMAC
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