Here at EXAIR, Coandă is a household name that can be heard on any given day multiple times throughout the day. The Coandă effect is fairly easy to visualize with a ligthweight ball and some high velocity airflow. Take the video below for example. This 2″ Super Air Amplifier on a stand powered at 40 psig at the inlet easily lifts this hollow plastic ball and then suspends the ball due to the Coandă effect.
If you were able to see the airflow, you would see it impacting the surface of the sphere at all different points then following the profile of the sphere until it colides with itself and is forced to separate off the surface. The turbulent flow on the top is creating a downward pressure as well. The science behind this was all found and showcased by Henri Coandă. He showcased this with a propulsion device which used a domed hood with airflow to follow the curvature of the dome then exit off the sharp edge or where the separate air streams began to recombine causing a turbulent / low pressure area depending on the angle.
This stream of air following a surface begins to pull in all surrounding and impacted air molecules from around the stream which is called entrainment. This is a key factor for EXAIR products and one reason the Coandă profiles are a key characteristic to obtaining the peak performance and efficiency out of a compressed air product.
Many EXAIR products utilize the Coandă principle to improve their efficiencies and performance. Below you can see the EXAIR product families containing Coandă profiles within their design which increases the ambient air entrainment resulting in an amplified air blowoff.
Here on the EXAIR blog we discuss pressure drops, correct plumbing, pipe sizing, and friction losses within your piping system from time to time. We will generally even give recommendations on what size piping to use. These are the variables that you will want to consider when selecting a piping size that will suit your need and give the ability to expand if needed.
The variables to know for a new piping run are as follows.
Flow Rate (SCFM) of demand side (products needing the supplied compressed air)
System Pressure (psig) – Safe operating pressure that will account for pressure drops.
Minimum Operating Pressure Allowed (psig) – Lowest pressure permitted by any demand side point of use product.
Total Length of Piping System (feet)
Piping Cost ($)
Installation Cost ($)
Operational Hours ( hr.)
Electical Costs ($/kwh)
Project Life (years) – Is there a planned expansion?
An equation can be used to calculate the diameter of pipe required for a known flow rate and allowable pressure drop. The equation is shown below.
A = (144 x Q x Pa) / (V x 60 x (Pd + Pa)
A = Cross-Sectional are of the pipe bore. (sq. in.).
Q = Flow rate (cubic ft. / min of free air)
Pa = Prevailing atmospheric absolute pressure (psia)
Pd = Compressor discharge gauge pressure (psig)
V = Design pipe velocity ( ft/sec)
If all of these variables are not known, there are also reference charts which will eliminate the variables needed to total flow rate required for the system, as well as the total length of the piping. The chart shown below was taken from EXAIR’s Knowledge Base.
Once the piping size is selected to meet the needs of the system the future potential of expansion should be taken into account and anticipated for. If no expansion is planned, simply take your length of pipe and start looking at your cost per foot and installation costs. If expansions are planned and known, consider supplying the equipment now and accounting for it if the additional capital expenditure is acceptable at this point.
The benefits to having properly sized compressed air lines for the entire facility and for the long term expansion goals makes life easier. When production is increased, or when new machinery is added there is not a need to re-engineer the entire system in order to get enough capacity to that last machine. If the main compressed air system is undersized then optimal performance for the facility will never be achieved. By not taking the above variables into consideration or just using what is cheapest is simply setting the system up for failure and inefficiencies. All of these considerations lead to an optimized compressed air system which leads to a sustainable utility.
In the beginning, when hearing and energy conservation were not a consideration, simple open pipes were used for blow off operations. These are a waste of compressed air, dangerously loud, and potentially injurious. Federal regulations have since been implemented requiring hearing protection from exposure to sound levels 90 dBA over a period of 8 hours or greater. It also mandates that if an orifice be dead ended against the skin it would not exhibit more than 30 psi.
Thirty years ago, EXAIR got its start making a more efficient nozzle that was O.S.H.A. compliant. The design sheltered the main air orifice down in a milled groove. The secondary orifice is an annular opening. This provides two functions. By chance if someone could find a way to block the main orifice, there is a secondary path for air to flow. The annular orifice also develops a tube of air surrounding the high velocity main air flow. This interaction deadens the sound level as well as creating a vacuum to draw in surrounding air.
The next step in the evolution is an air jet which utilizes the coanda effect which is the phenomenon where high velocity air will adhere to a surface. Compressed air is injected through an annular orifice at sonic velocity. The injected air is directed toward the output and creates a vacuum on the opposite end. This vacuum pulls in large volumes of free air and results in a larger volume of air on to the target. If one end or the other is blocked, flow simply reverses at well below OSHA dead ended pressure requirements.
Similar in design concept but in larger configurations is the air amplifier. They move massive amounts of air which makes them an ideal solution for cooling, ventilating, and for blow off. Two styles were developed. An adjustable style were the annular orifice can manually be adjusted to control air flow and force. The second design has a fixed flow where the annular orifice is established with a patented shim.
The more recent improvement on the safety nozzle is the Super Air Nozzle. The design concept here is to embed the orifices between fins around the perimeter of the nozzle. This prevents blockage by providing a path fore and aft for air to escape and remain below the OSHA dead end pressure threshold. The high velocity air also creates a low pressure area drawing in up to 25 times in volume of surrounding ambient air than the volume of compressed air consumed. Sound levels are also greatly reduced.
EXAIR is not done exploring new and improved compressed air products. Product design is customer driven so we welcome your feedback.