We often run into situations where a customer does not have enough compressed air volume to implement a solution. This leaves three possible options. 1) Abandon the project all together and continue to feel the pain the problem creates. 2) Install a larger compressor, with associated expense. 3) Install a secondary, or “point of use” receiver tank to store the compressed air volume local to the application, to be available immediately without having to rely on the distribution system for storage capability. This 3rd option is a cost-effective solution customers often use to mitigate the impact of installing a new compressed air consuming product onto the system.
Large demand events on a compressed air system can leave the system short on air. This can result in a system pressure drop which is undesirable. Utilizing a secondary receiver tank to mitigate the impact of larger volume consuming events is a common and useful strategy that many compressed air professionals will recommend and pursue. In this kind of scenario, the receiver tank acts much like a capacitor in a camera flash. A camera battery charges a capacitor which then dumps its charge into the flash bulb when you take a photo for a notably bright flash which is what one generally wants from their camera flash.
In this same way, a receiver tank acts like the capacitor to “dump” the air volume needed to make a compressed air device work at its design pressure and flow for some prescribed period of time. In situations like this, the high demand does need to be an intermittent one so that the tank can then re-charge from the compressor system and be ready for the next air use event. This means that certain calculations need to be made to ensure that the receiver tank is sized properly to provide the desired effect.
How do you size a receiver tank? Here’s the calculation to determine the proper size:
Let’s consider an example of an Air Amplifier solution. A customer wants to blow on hot metal parts coming out of an oven to cool them down as an “air quench”. We evaluate the application and determine that (2) 2″ Super Air Amplifiers will provide the right amount of flow. Those units are going to operate at 60 PSIG to provide the desired effect. (2) 2″ Super Air Amplifiers will consume 24.5 SCFM @ 60 PSIG. Each batch of parts comes out of the oven at a rate of one batch every 5 minutes. They want to provide the necessary cooling for a total of 30 seconds to have the air quench effect. So, every 5 minutes, the Air Amplifiers will be blowing for 1/2 minute. Each “on” event consumes 12.25 Standard Cubic Feet of air. We then have 4 minutes, 30 seconds left to re-plenish the tank.
The last piece of information we need to know is the system pressure for the compressed air header feeding the tank. The system pressure is 120 PSIG. And so, our calculation looks like this:
V = 0.5 min. x 24.5 rate of flow x (60 PSIG + 14.5 PSIA)
120-60
V = 913
60
V = 15.2 ft.3
There are 7.48 gallons to a cubic foot, so our receiver tank in this example would be
15.2 ft.3 x 7.48 = 114 gallons.
Given the fact that receiver tanks are made in certain, standard sizes, a 120 gallon tank or two, 60 gallon tanks piped in upstream of the compressed air load would be appropriate for this application.
As a further note to the example, the refill rate to the tank(s) would need to be a minimum of 2.72 SCFM to get the volume replenished in time for the next event. This is less than 1 HP of industrial air compressor to maintain such a flow rate to refill the tank.
With some reasonably simple math to determine tank size, and a willingness to pursue this kind of air delivery solution, you can implement that compressed air solution at a fraction of the cost compared to a new compressor.
EXAIR LLC
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Cover Photo by dkeissling and licensed by Pixabay
