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.