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Technology, Service, Parts & Maintenance

The Difference Between Pressure and Flow


When it comes to compressed air systems, pressure and flow are two of the most common terms you’ll encounter. Pressure and flow help facilities size their compressors to power applications with the proper air volume and flow rate so that no energy is wasted.

So what exactly is air pressure?

Pressure determines the compressor’s ability to perform a specified amount of work at any given point in time. The compressor must provide the right amount of pressure, or force, needed to complete the process. Too little pressure means the job won’t get done, whereas too much pressure can damage the equipment and cause unexpected malfunctions.

How is pressure measured?

Pressure is measured in pounds per square inch (psi).

What is flow?

Flow is the compressor’s ability to continue performing a certain task. The amount of flow needed depends on the length of time required to complete the task. With insufficient flow, the compressor will require breaks to rebuild pressure in the compressor’s reserve tank.

How is flow measured?

Flow is measured in cubic feet per minute (cfm) at a specific pressure.

How do pressure and flow work together?

Now that we know what these terms mean, let’s take a look at the relationship between pressure and flow. Say we need to move a 10 lb. block across a long table. While 100 psi of air pressure may not be enough force to move the block, 115 psi will, which is why it’s important to know the minimum pressure needed for your process. Blindly increasing pressure can cause an unnecessary increase in energy consumption. Simply increasing pressure by 2 psi causes a 1 percent increase in the energy needed to maintain the same airflow.

block-psi illustration.jpg

Airflow takes into consideration how often you need to move the 10 lb. block across the table. If the block only needs to move a small distance every hour then a small compressor with a small air tank can meet those demands. However, if your application requires that you keep the block constantly moving over a span of many hours then you’ll need a larger compressor with more continuous flow. 

block-cfm illustration.jpg

Understanding pressure and flow will help you size your compressor based on process demands while reducing energy requirements, improving productivity and lowering lifecycle costs.

Have questions about the relationship between pressure and flow? Leave us a comment below or send us an email on our contact page.

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