Positive-displacement and dynamic displacement compressors are the two high level principles for the generation of compressed air or gas. Positive displacement types are the most common found in industrial facilities. These units draw ambient air into a chamber which it seals off and then works to compress and squeeze it down into a smaller volume. The air is then discharged into the outlet system of the compressor. Out of the many types of positive displacement compressors, today we are going to discuss the rotary style positive displacement air compressors.
These are available in both lubricant-free as well as lubricant-injected versions. The main function of the compressor is the same, both have two inter-meshing rotors what pull air into the inlet port and then after the rotational processing of the compressor the air is discharged through a discharge port. The in between of the ports is where the important information lies. The air after being sucked into the inlet gets pulled in between two lobes and the stator. As the air is being trapped the space between the lobes becomes increasingly smaller, thus increasing the pressure of the air transferring it to the discharge port.
The lubricated versions will often help to dissipate the heat that is created as the air is being compressed. This lubricant is then possible to transfer into the compressed air stream and must be removed before a point of use product if lubricant-free air is needed for the process. These compressors rank amongst the lower efficiencies in the positive displacement air compressors.
If you are visual learner, feel free to take a few minutes for the video below.
If you would like to discuss the way to get the most out of your compressor, no matter the type, contact an Application Engineer and let us help you determine the most efficient way to use the air effectively.
Brian Farno Application Engineer BrianFarno@EXAIR.com @EXAIR_BF
Centrifugal air compressors are one example of dynamic style air compressors. The dynamic type of compressors have a continuous flow of air that has its velocity increased in an impeller that is rotating at a higher speed. The kinetic energy of the air is increased due to the increase in velocity and then becomes transformed into pressure energy through the use of a volute chamber, or a diffuser. The volute chamber is a curved funnel that increases in surface are as it approaches the discharge port. This converts the kinetic energy into pressure by allowing the velocity to reduce while the pressure increases. Approximately 1/2 of the energy is developed in the impeller and the other half is developed in the volute chamber or diffuser.
The most common centrifugal air comppressor has between two and four stages in order to generate pressures up to 150 psig. A water cooled inter-cooler and separator is placed between each stage in order to remove condensation and cool the air down prior to being passed on to the next stage. These compressors still have advantages and some disadvantages. The list below showcases just a few.
Lubricant-free air is generated
Complete packages up to 1,500 hp
Initial costs decrease with increase in compressor size
No special foundations or reinforcements needed
Specialized maintenance requirements
Higher initial investment
Unloading/waste of air required to drop system pressures
To determine which type of compressor may be best suited for your facility, we suggest to locate and contact a compressor sales company in your geographic area. When it comes to determining the volume of air required to operate the EXAIR products and even some other point of use compressed air applications, EXAIR’s Application Engineers can help you determine the volume you will need to ensure the compressor is sized appropriately. If you would like to discuss any other point of use application, please contact us.
When it comes to generating compressed air there are many types of compressors to utilize within a facility. One of those types is a dual acting reciprocating compressor. This is a type of positive displacement compressor that takes advantage of a piston style action and actually compresses air on both directions of the stroke. Below you can see a video from a company that showcases how a dual acting compressor works and gives a good representation of how it is compressing the air on both directions of travel.
The reciprocating type of air compressor uses a motor that turns a crank which pushes a piston inside a cylinder; like the engine in your car. In a basic cycle, an intake valve opens to allow the ambient air into the cylinder, the gas gets trapped, and once it is compressed by the piston, the exhaust valve opens to discharge the compressed volume into a tank. This method of compression happens for both the single and double acting reciprocating compressors.
With a single acting compressor, the air is compressed only on the up-stroke of the piston inside the cylinder. The double acting compressor compresses the air on both the up-stroke and the down-stroke of the piston, doubling the capacity of a given cylinder size. This “double” compression cycle is what makes this type of air compressor very efficient. A single acting compressor will have an operating efficiency between 100 cfm / 23 kW of air while the double acting compressor has an operating efficiency between 100 cfm 15.5 kW . Therefore, electricity cost is less with a double-acting reciprocating air compressor to make the same amount of compressed air.
These compressors are ruggedly designed to be driven 100% of the time and to essentially be a Clydesdale of compressors. They are commonly used with applications or systems requiring higher pressures and come in lubricated or non-lubricated models.
If you would like to discuss air compressors or how to efficiently utilize the air that your system is producing so that you aren’t giving your compressor an artificial load that isn’t needed, contact us.
Evaluating all of the different types of compressors and which is right for you can seem like a daunting task. Today, I’d like to take some time to talk about the Double-Acting Reciprocating type of air compressor.
Double-Acting Reciprocating compressors are a subset of the larger family of positive displacement compressor types. In positive displacement compressors, air is drawn into a chamber where the volume is then mechanically reduced. The energy used to displace the air volume is converted to an increase in air pressure. Dynamic compressors operate a little differently. They utilize an increase in air velocity to create the change in pressure. Air is accelerated to a high velocity through an impeller. The kinetic energy of the air is converted to an increase in potential (pressure) energy.
The Double-Acting Reciprocating compressor is a close relative to the Single-Acting Reciprocating compressor. In these types of compressors, an “automotive-type” piston driven by a crankshaft provides the compression. In a Double-Acting Reciprocating compressor, air is compressed as the piston moves in each direction. Hence the name, “double-acting”. In a Single-Acting Reciprocating compressor, air is only compressed on each full revolution of the piston. This makes the Double-Acting Reciprocating compressor much more efficient than its brethren.
Double-Acting Reciprocating compressors are also available in much larger sizes. While Single-Acting compressors can be found up to 150HP, generally they’re much less common any larger than 25HP. Whereas a Double-Acting compressor is available from 10HP-1,000HP, making it a better choice for larger plants that require a significantly greater volume of compressed air. While they’re a bit more expensive due to the added mechanisms to produce the double-action compression, this cost is quickly offset by the increase in efficiency. At a performance of 15-16 kW/100 cfm, they’re 32% more efficient than a single-acting reciprocating compressor.
If you’re in the market for a new compressor and are struggling to determine the most suitable compressor, talk with your local compressor sales representative. Once you’re up an running, EXAIR has a wide-range of products that’ll make sure you’re using your compressed air safely and efficiently!