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All pneumatic systems using compressed air will feature an air receiver, whether this is a small compressor with an integral receiver or a standalone compressor with a separate air vessel.
The air receiver is a vital part of the compressed air system and has 2 main purposes. It acts as a container for the compressed air storing it for when demand increases and acts as a buffer for the compressor limiting the number of times the compressor has to turn on and off to refill the receiver.
This is why it’s so crucial to correctly size the tank required for your application. If your receiver is too small for your application this will result in a high workload for the compressor resulting in a shorter life span and increased maintenance both of which are costly and unnecessary.
Air Receiver Size Based on CFM Requirement
The volume of compressed air storage required depends on a few factors.
- The capacity of the compressor in cfm (cubic feet per minute).
- The peak cfm requirements at the maximum demand of the system.
- The consistency of airflow.
- The internal diameter of the pipework used within the system.
- The type of air compressor required
A general rule for most applications is to have 10-15 litres of air capacity per cfm output required. If your compressor is rated for 35cfm then you would want a receiver tank between 500 litres to 900 litres. The first thing that needs to be done is to calculate the maximum air consumption required in CFM at peak usage.
To do this will need to work out the air demand of each tool or consumer that will be used at the same time and then multiply this by a utilisation factor for each item.
The utilisation factor refers to how a tool is used and how that affects the airflow. E.g. if you have an impact wrench that has an air consumption of 20 CFM at 100PSI that you need to use for 20 seconds at a time, initially the tool will consume the full 20cfm but as it gets closer to completing the desired task it will use less air.
An example of this is if the impact wrench is being used in a garage to tighten lug nuts initially there will be almost no resistance but as the torque begins to rise on the nut the wrench will consume less air until the final torque is achieved. The wrenches air consumption under load is not the same throughout this process and the time between tightening the lug nuts also varies. This difference between the CFM load and the times becomes the utilisation factor.
Even if a tool is rated at 20cfm it doesn’t actually mean that the tool requires the full rated CFM to complete the task nor always does it require the full 20 seconds to complete the task.
What Else Needs to be Taken into Account?
If your compressed air system features fluctuations during high demand times then you will require a larger storage vessel than a system with a steady predictable airflow.
A steady air flow system such as a robotic system that uses a consistent amount of air over some time will require a smaller receiver than a manufacturing plant that features a varying number of stations being operated throughout the day.
The internal diameter of the pipework being used within the system also affects the receiver size required as the pipework itself will store air. The larger the diameter of the pipework the more air it will store resulting in a larger overall storage capacity.
This calculation needing to be factored in will depend on the total amount of pipe being used within the air system and may not always be a factor that needs consideration.
Air Receiver Tanks for Compressors
There are two main types of air compressors available and the sizing of the required receiver tank will be different depending on if you’re using a reciprocating or rotary compressor.
A reciprocating compressor requires a receiver to store compressed air to minimise pulsation. Once the tank has been filled with enough air the tools and consuming equipment can then be used. When in use the equipment can drain the tank quickly resulting in wasted time waiting for the tank to refill, this is why it is so important to ensure the correct tank size is calculated to increase productivity and reduce downtime and unnecessary maintenance on an overworked compressor.
To ensure you size the correct tank a standard rule is to work out the tool or consuming part that has the highest CFM requirement at the required PSI and then multiply the CFM requirement by 4.75 or 5.8 and round up to the nearest available tank size. For example, if the CFM requirement is 20 CFM then 20 x 4.75 = 90ltr and 20 x 5.8 = 116ltr making the suggested tank size 100ltrs or 150ltrs depending on your application.
For a rotary screw compressor an air receiver may not be required. A rotary screw compressor works by supplying an uninterrupted constant flow of compressed air, meaning that as long as the tools being used require less CFM than the compressor is producing then there won’t be an issue.
Although applications featuring heavy duty tools or with high CFM outputs you could invest in a small receiver tank to ensure the compressor will always operate at peak performance.
Conclusion
Sizing an air receiver tank is a complicated, time-consuming, and critical process. With so many different sizes and configurations available it’s difficult to know where to start especially since your choice can detrimentally affect the efficiency of your application.
To ensure your application is set up for peak performance get in touch with one of our experts today at 01634 297298 to discuss your requirements and what the best solution is for you. Alternatively you can send your application details and requirements to sales@fluid-air.co.uk.
