A rotary-screw compressor is an air compressor that uses a rotary-type positive-displacement mechanism, typically used replace piston compressors where
large volumes of high-pressure air are needed, either for large industrial applications or to operate high-power air tools.
What are twin screw compressors?
The principle for a rotating displacement compressor in twin screw form was developed during the 1930s, when a rotating compressor with high flow
rate and stable flow under varying pressure conditions was required. The twin screw element's main parts are the male and female rotors, which
rotate in opposite directions while the volume between them and the housing decreases.
Each screw element has a fixed, build-in pressure ratio that is dependent on its length, the pitch of the screw and the form of the discharge port.
To attain maximum efficiency, the build-in pressure ratio must be adapted to the required working pressure. The screw compressor is generally
not equipped with valves and has no mechanical forces that cause unbalance. This means it can work at a high shaft speed and can combine a
large flow rate with small exterior dimensions. An axial acting force, dependent on the pressure difference between the inlet and outlet, must
be overcome by the bearings.
Oil-free screw compressors
The first twin screw compressors had a symmetric rotor profile and did not use any cooling liquid inside the compression chamber. These were called
oil-free or dry screw compressors. Modern, high-speed, oil-free screw compressors have asymmetric screw profiles, resulting in significantly
improved energy efficiency, due to reduced internal leakage. External gears are most often used to synchronize the position of the counter-rotating
rotors. As the rotors neither come into contact with each other nor with the compressor housing, no lubrication is required inside the compression
chamber.
Consequently, the compressed air is completely oil-free. The rotors and housing are manufactured with ultimate precision to minimize leakage from
the pressure side to the inlet. The build-in pressure ratio is limited by the limiting temperature difference between the inlet and the discharge.
This is why oil-free screw compressors are frequently built with several stages and interstage cooling to reach higher pressures.
How do liquid-injected screw compressors work?
In liquid-injected screw compressors, a liquid is injected into the compression chamber and often into the compressor bearings. Its
function is to cool and lubricate the compressor element's moving parts, to cool the air being compressed internally, and to reduce the
return leakage to the inlet. Today oil is the most commonly injected liquid due to its good lubricating and sealing properties, however,
other liquids are also used, for example, water or polymers. Liquid-injected screw compressor elements can be manufactured for high
pressure ratios, with one compression stage usually being sufficient for pressure up to 14 and even 17 bar, albeit at the expense of
reduced energy efficiency.
Fixed Speed Compressors vs. Variable Speed Drive Compressors (VSD)
The basic difference between the two technologies can be found right in the name. Fixed speed compressors run at a continuous fixed speed and tend to be
very efficient when operating at 100% of its capacity, meaning when the motor is running and compressed air is being manufactured. The inefficiency
of a fixed speed compressor is very noticeable and can easily be measured when the unit unloads and stops making air. Before the motor comes to a complete
stop, it will continue to run while no air is being produced, consequently wasting energy and money. Inefficiency and waste can especially be visible
at facilities that operate multiple shifts and or have great flow demand fluctuation throughout the day.
Variable speed drive (VSD) technology works on a different principle, as it turns the motor at the appropriate speed in relation to the amount of air
that is required within a given plant / facility. In simpler terms, as the need / demand for air increases, so does the speed of the motor, therefore
supplying more flow / CFM. On the other hand, if the demand decreases, the motor will automatically slow down and only use the required energy to provide
appropriate flow. VSD air compressors match the output to the demand that is needed and can sense how much flow is being used, while adjusting its
speed accordingly. On slower production days, break throughout the day, or during second and third skeleton shifts, the VSD technology comes especially
handy, as it eliminates the waste of electricity, therefore saving money.
Considering that compressed air usage is costly, as it accounts for over 70% of Total Cost of Ownership in electricity costs, utilizing VSD technology
can help you achieve savings of 35-50%. Depending on size of the compressor, the savings can range from $100s to $10,000s annually or more, making
it an ideal investment for any facility. VSD air compressors are becoming the norm rather than an exception, with many customer enjoying the annual
energy savings and having the ability to reinvest the money into other assets.
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Who we are and how Ash Air can help your business!
Ash Air has been around in New Zealand since 1979, and we’ve grown into a nationwide company with international support and a
reputation for quality and reliability.We look after all things compressed air for your business!
Reciprocating, Screw, air compressors
Vacuum pumps
Nitrogen
An extensive line of air treatment components
Ash Air's range of Chicago Pneumatic, Alup, Pneumatech, and Quincy compressors are used extensively around the world in industries
ranging from oil and gas to food, automotive and farming, and we bring you these world class compressors here in the land of the long white
cloud.Our technicians are compressed air equipment experts and are dedicated to addressing customer needs. Supported by a 13 locations
nationwide, Ash Air offers one of the widest selections of compressed air equipment and parts available today in New Zealand.
Reliability and Efficiency
With Ash Air compressors, you can count on reliability and high performance for even the most demanding applications. We focus our
efforts on the following:
Air compressors come in many types, rotary screw, piston, scroll, reciprocating, some are oil-free and other air compressors require oil
lubrication. Like many businesses, an efficient air compressor is at the heart of their operations. So, which type of compressor should you
choose? What makes a compressor, like a rotary screw, unique? Here are some clear cut benefits of equipping your business with a rotary
screw compressor.
Read More…
In the world of compressors, there are often significant and unutilized energy-saving possibilities including energy recovery, pressure
reduction, leakage reduction and optimization of operations through correct choice of a control and regulation system as well as the choice
of compressor size.We are going to take a look at some of the opportunities for minimizing the compressor’s operating costs.
Read More…
Many installations that produce compressed air offer significant and frequently unutilized energy
saving possibilities in
the form of waste energy recovery. In large industries, energy costs can amount to 80% of the total cost of compressed
air production.
However, a lot of this energy can be recovered, which in turn will save you a lot of money.
Read More…
Liquid water in compressed-air systems can lead to rusted equipment and unresponsive controls. Anyone who uses compressed air will, at some
point, find liquid water in the air distribution system. This can be anything from a nuisance to a serious problem, depending on the
application. If water might corrode equipment or introduce bacteria, removing it is critical.
Read More…
Liquid water in compressed-air systems can lead to rusted equipment and unresponsive controls. Anyone who uses compressed air will, at some
point, find liquid water in the air distribution system. This can be anything from a nuisance to a serious problem, depending on the
application. If water might corrode equipment or introduce bacteria, removing it is critical.
Read More…
Whenever most people think about a compressor, they probably have a piston compressor in mind. You might already know there are two basic
principles of air compression. One of those is the principle of displacement compression. There are a lot of compressor types that classify
as a displacement compressor. The piston compressor is one of them, oil-lubricated or oil-free.
Read More…
Once you have the size and type of
compressor figured out, one last question remains, should I go with an oil lubricated or oil-free air compressor. To not overcomplicate the
answer, your choice should be based on the application and process that the compressed air will be utilized in.
Read More…
Like all compressor types, rotary screw models do require periodic maintenance. Thanks to the simplicity of the internal components,
maintenance is relatively easy on most rotary air compressors. As long as you stick to a rotary screw compressor maintenance schedule, you
will likely be rewarded with many, many years of optimal productivity from your machine.
Read More…
Did you know, the biggest part of the air we breathe is nitrogen? Everyone needs oxygen to survive, however air is made up of 78% nitrogen,
only 21% oxygen and tiny amounts of other gases. Although, the human body does not use this nitrogen, it is very helpful in various
industrial applications. There is an unlimited source of nitrogen readily available, allowing you to achieve needed purity at a fraction of
your current annual nitrogen cost.
Read More…
If you notice that your compressor is getting hot and bothered, there may be heating issues affecting your air compressors performance. Did
you know that an overheating compressor is top of the pops for being the most common cause of compressor failure.
Read More…
A rotary-screw compressor is an air compressor that uses a rotary-type positive-displacement mechanism, typically used replace piston
compressors where large volumes of high-pressure air are needed, either for large industrial applications or to operate high-power air
tools.
Read More…
Have a look around and what do you see? What are you thinking about? Your next holiday to Queenstown maybe? You might go snowboarding with
the kids or have some alone time at the Day Spa. Whatever holiday you choose, compressed air is involved in some way, without you even
realising it!
Read More…
There are crucial reasons why you should service and maintain your compressor regularly, with the most common issues being piston failure
caused by wear of components, increased friction, corrosion, reduced cooling, overheating bearings and components, clogging of air filters.
Read More…
Our passion for energy efficiency and cost saving derives from the concern for our children’s future. Analysing the efficiency of your
system is a brilliant way to start saving.
Read More…
Compressed air is all around us, from the air in a balloon to pumping up tires on your bicycle. In this article we will explain what
compressed air is and how it is created. Whether you know it or not, compressed air is involved in every aspect of our lives, from the
balloons at your birthday party to the air in the tires of our cars and bicycles. It was probably even used when making the phone, tablet or
computer you’re viewing this on.
Read More…
One of the biggest challenges is to correctly size your new air compressor. Similarly to everything else, new compressors available on the
market are more efficient and employ better technology, therefore you have to understand the application and usage to size the machine
correctly. Choosing the wrong air compressor for your facility can lead to problems with production and or increased costs due to wasted
energy.
Read More…
Once you have the size of the air compressor figured out, the
next thing to do is to decide on the type of compresor you will need for your application - piston, rotary screw compressor etc. Let us take
a look at two of the most popular options available. When choosing the right type of compressor, you should ask yourself the following
questions:
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Which vacuum pump do I need? - this is one of the most frequent questions we receive and this is understandable, because there are number
of technologies which can provide the same vacuum level and pumping speed. Here is quick advice on how to choose the best vacuum pump for
your needs.
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You may be asking, why does my air compressor start, then stop? Allow us to take the guessing out of it. We understand your pain. We know
that a compressor problem can quickly result in hours (if not days) of production downtime and loss of revenue. When your compressor
continuously shuts off from on, we refer that as a short cycle. There are a few reasons that a short cycle may be happening with your
compressor.
Read More…
Air compressor leaks are very common in all applications, but can be very costly and difficult to find. On average, 20-30% of the compressed
air used in a manufacturing plant is wasted as leaked air. Finding and fixing these leaks can save your business thousands of wasted dollars
a year.
Read More…
When installing a compressed air system into a business, people often look to PVC piping as an option to build a piping system because it is
cheap, versatile and easy to install. However, using PVC pipe in any compressed air application is extremely dangerous and NOT recommended
by multiple associations and manufacturers.
Read More…
Changing the oil and oil filters on your compressor is one of the most common routine maintenance tasks to perform to keep your compressor
running efficiently. After you remove your old oil and oil filter, you may find yourself wondering, “Where do I dispose of these?”, or “Can I
just throw them in the trash?”. Because oil is toxic and a pollutant, disposing of your old oil and filters is not as simple as just tossing
them in the trash.
Read More…
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