# How to Calculate the Size of a Compressed Air Tank

by Paul Richard
people at work, air compressor image by Greg Pickens from <a href='http://www.fotolia.com'>Fotolia.com</a>

Compressed air tools are widely used in commercial and residential applications for repairs, painting and other uses. A key part of a compressed air system is the compressed air tank or receiver. The air tank acts as a storage vessel to provide adequate air supply to the tools you are using and helps the air compressor operate efficiently by smoothing out pressure fluctuations. It is estimated that 70 percent of manufacturers have a compressed air system. You need to calculate the correct tank size for your air requirements to avoid installing an undersized tank providing too little air or an oversized tank which wastes energy by requiring the compressor to run longer.

#### Step 1

List the compressed air tools you use. Obtain the air flow and pressure requirements of each tool. The tool specifications are often printed or stamped on the tool (wording such as "2 cubic feet per minute (cfm) at 100 pounds per square inch (psi)") and will determine the tool requirement.

#### Step 2

Calculate the total airflow requirement for all tools by adding together the airflow required for each tool. You should overestimate tool airflow requirements to prevent under-sizing the receiver. Under-sizing is calculating a volume too small for the required airflow, which would result in too little air capacity. As an example, your compressed air system may supply air to several work stations. You need to assume all stations are using air simultaneously to provide proper capacity.

#### Step 3

Use the total airflow requirement and estimate the amount of time a maximum air capacity will be needed. For example, if all needed tools require 20 cfm for a maximum of 15 minutes per hour, then the minimum volume is (20 cfm) x (15 min) = 300 cubic feet. So the minimum air required is 300 cubic feet.

#### Step 4

Calculate the required tank volume. The calculation based on time required for the compressor to run uses the equation "t = V (p1 - p2) / C pa" (Time for receiver to go from upper pressure limits (min) = Volume of Receiver Tank (cuft) (Maximum Tank Pressure (psi) x minimum tank pressure (psi)) / Air Needed (cfm) x 14.7 psi). Or you can estimate tank size in one of two ways; use actual cfm from Step 3 above or assume 4 gallons capacity for every compressor horsepower.

Consider using more smaller compressors versus one large compressor. The energy savings from smaller compressors can be significant because maximum capacity may only be needed intermittently. One large compressor will run under capacity most of the time which is inefficient.

#### Items you will need

• Calculator
• List of compressed air tools you use