How-To Size Receiver Tanks and Why Use Them in Your Compressed Air System

Receiver Tank

My colleague, Lee Evans, wrote a blog about calculating the size of primary receiver tanks within a compressed air system.  (You can read it here: Receiver Tank Principle and Calculations).  I would like to expand a bit more about secondary receiver tanks.  They can be strategically placed throughout the plant to improve the operation of your compressed air system.  The primary receiver tanks help to protect the supply side when demands are high, and the secondary receiver tanks help pneumatic systems on the demand side for optimum performance.

Circuit Board

I like to compare the pneumatic system to an electrical system.  The receiver tanks are like capacitors.  They store energy produced by an air compressor like a capacitor stores energy from an electrical source.  If you have ever seen an electrical circuit board, you notice many capacitors with different sizes throughout the circuit board (reference photo above).  The reason for this is to have a ready source of energy to increase efficiency and speeds with the ebbs and flows of electrical signals.  The same can be said for a pneumatic system with secondary receiver tanks.

To tie this into the compressed air system, if you have an area that requires a high volume of compressed air intermittently, a secondary receiver tank would benefit this type of pneumatic setup.  With valves, cylinders, actuators, and pneumatic controls which turn on and off, it is important to have a ready source of stored “energy” nearby.

For calculating a minimum volume size for your secondary receiver tank, we can use Equation 1 below.  It is the same for sizing a primary receiver tank, but the scalars are slightly different.  The supply line to this tank will typically come from a header pipe that supplies the entire facility.  Generally, it is smaller in diameter; so, we have to look at the air supply that it can feed into the tank.  For example, a 1” NPT Schedule 40 Pipe at 100 PSIG can supply a maximum of 150 SCFM of air flow.  This value is used for Cap below.  C is the largest air demand for the machine or targeted area that will be using the tank.  If the C value is less than the Cap value, then a secondary tank is not needed.  If the Cap is below the C value, then we can calculate the smallest tank volume that would be needed.  The other value in the equation is the minimum tank pressure.  In most cases, a regulator is used to set the air pressure for the machine or area.  If the specification is 80 PSIG, then you would use this value as P2P1 is the header pressure that will be coming into the secondary tank.  With this collection of information, you can use Equation 1 to calculate the minimum tank volume.  So, any receiver tank with a larger volume would work as a secondary receiver tank.

Equation 1:

V = T * (C – Cap) * (Pa) / (P1-P2)

Where:

V – Volume of receiver tank (cubic feet)

T – Time interval (minutes)

C – Air demand for system (cubic feet per minute)

Cap – Supply value of inlet pipe (cubic feet per minute)

Pa – Absolute atmospheric pressure (PSIA)

P1 – Header Pressure (PSIG)

P2 – Regulated Pressure (PSIG)

If you find that your pneumatic devices are lacking in performance because the air pressure seems to drop during operation, you may need to add a secondary receiver to that system.  EXAIR stocks 60 Gallon tanks, model 9500-60, to add to those specific areas.  If you have any questions about using a receiver tank in your application, primary or secondary, you can contact an EXAIR Application Engineer.  We can restore your efficiency and speed back into your applications.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Photo: Circuit Board courtesy from T_Tide under Pixabay License

Intermediate Storage Tanks & How To Size Them

When evaluating processes that utilize compressed air and adhering to the Six Steps to Compressed Air Optimization, intermediate storage proves to be a critical role coming in at step number five. Intermediate storage tanks may already be in place within your facility and often times can be implemented as modifications to aid existing lines that are struggling to maintain proper availability of compressed air to keep the line at peak performance.

EXAIR Receiver Tank in 60 Gallon Capacity

When determining whether or not a production line or point of use compressed air operation would benefit from a receiver tank/intermediate storage we would want to evaluate whether the demand for compressed air is intermittent.  Think of a receiver tank as a capacitor in an electrical circuit or a surge tank in a water piping system.  These both store up energy or water respectively to deliver to during a short high demand period then slowly charge back up from the main system and prepare for the next high demand.   If you look from the supply point it will see a very flattened demand curve, if you look from the application side it still shows a wave of peak use to no use.

Intermittent Applications are prime for rapid on/off of compressed air.

One of the key factors in intermediate storage of compressed air is to appropriately size the tank for the supply side of the system as well as the demand of the application.  The good news is there are equations for this.  To determine the capacity, use the equation shown below which is slightly different from sizing your main compressed air storage tank.  The formulate shown below is an example.

Where:

V – Volume of receiver tank (ft3 / cubic feet)

T – Time interval (minutes)

C – Air demand for system (cubic feet per minute)

Cap – Supply value of inlet pipe (cubic feet per minute)

Pa – Absolute atmospheric pressure (PSIA)

P1 – Header Pressure (PSIG)

P2 – Regulated Pressure (PSIG)

One of the main factors when sizing point of use intermediate storage is, they are being supplied air by smaller branch lines which cannot carry large capacities of air.  That limits your Cap value. The only way to decrease the V solution is to increase your Cap. The other key point is to ensure that all restrictions feeding into the tank and from the tank to your point of use are minimized in order to maintain peak performance.

If there are intermittent applications that are struggling to keep up with the production demands within your system, please reach out and speak with an Application Engineer.  We are always here to help and we may even be able to help you lower the demand needed by utilizing an engineered point of use compressed air solution.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF