A receiver tank is a form of dry compressed air storage in a compressed air system. Normally installed after drying and filtration, and before end use devices, receiver tanks help to store compressed air. The compressed air is created by the supply side, stored by the receiver tank, and released as needed to the demand side of the system.
But how does this work?
The principle behind this concept is rooted in pressure differentials. Just as we increase pressure when reducing volume of a gas, we can increase volume when reducing pressure. So, if we have a given volume of compressed air at a certain pressure (P1), we will have a different volume of compressed air when converting this same air to a different pressure (P2).
This is the idea behind a receiver tank. We store the compressed air at a higher pressure than what is needed by the system, creating a favorable pressure differential to release compressed air when it is needed. And, in order to properly use a receiver tank, we must be able to properly calculate the required size/volume of the tank. To do so, we must familiarize ourselves with the receiver tank capacity formula.
Receiver tank capacity formula
V = ( T(C-Cap)(Pa)/(P1-P2) )
V = Volume of receiver tank in cubic feet
T = Time interval in minutes during which compressed air demand will occur
C = Air requirement of demand in cubic feet per minute
Cap = Compressor capacity in cubic feet per minute
Pa = Absolute atmospheric pressure, given in PSIA
P1 = Initial tank pressure (Compressor discharge pressure)
P2 = minimum tank pressure (Pressure required at output of tank to operate compressed air devices)
Let’s consider an application with an intermittent demand spike of 50 SCFM of compressed air at 80 PSIG. The system is operating from a 10HP compressor which produces 40 SCFM at 110 PSIG, and the compressed air devices need to operate for (5) minutes at this volume.
We can use a receiver tank and the pressure differential between the output of the compressor and the demand of the system to create a reservoir of compressed air. This stored air will release into the system to maintain pressure while demand is high and rebuild when the excess demand is gone.
In this application, the values are as follows:
V = ?
T = 5 minutes
C = 50 CFM
Cap = 40 SCFM
Pa = 14.5 PSI
P1 = 110 PSIG
P2 = 80 PSIG
Running these numbers out we end up with:
This means we will need a receiver tank with a volume of 24.2 ft.³ (24.2 cubic feet equates to approximately 180 gallons – most receiver tanks have capacities rated in gallons) to store the required volume of compressed air needed in this system. Doing so will result in a constant supply of 80 PSIG, even at a demand volume which exceeds the ability of the compressor. By installing a properly sized receiver tank with proper pressure differential, the reliability of the system can be improved.
This improvement in system reliability translates to a more repeatable result from the compressed air driven devices connected to the system. If you have questions about improving the reliability of your compressed air system, exactly how it can be improved, or what an engineered solution could provide, contact an EXAIR Application Engineer. We’re here to help.