Air Pressure Vs. Flow

When discussing compressed air systems, pressure and flow are integral parts of how a system will utilize the air. Air pressure determines how a system will perform a specific task, whereas airflow is the system’s ability to perform the task continuously. These standard terms are often misunderstood in regards to compressed air systems. Understanding pressure and flow will be essential not to waste energy.

Pressure: What is It and How is It Measured?

Air pressure is a force exerted by the air on any surface in contact with it, whether unconfined or compressed. Pressure in a compressed air system, as noted above, determines the system’s ability to perform work. Too much pressure and the equipment is damaged, too little, and the task is impossible to complete.

The pressure is measured in pounds per square inch(psi). Let’s say the air gauge on a compressor reads 20psi. What this signifies is that for every square inch, there are 20 pounds of pressure applied.

Flow: What is It and How is It Measured?

As a measure of volume, flow indicates a system’s output rate. The length of time to complete the task is what will determine the amount of airflow. A compressor will need to stop and rebuild pressure in the tank if it does not have sufficient flow for the job.

Cubic feet per minute(cfm) is how the flow is measured at a specific pressure. This measurement will increase in direct proportion to the horsepower applied. Simply put, a compressor with a higher cubic feet per minute rating will provide more air.

Below we have recapped the measurements of a compressed air system. No matter the task, it’s imperative a facility understand PSI, CFM, and HP.

PSI – This measures the amount of pressure per square inch. For a compressor, it is the amount of force it can deliver.

CFM – The flow rate of a compressor. The amount of air a compressor can produce at a given level of pressure.

HP – The horsepower is the amount of work performed by a compressor’s motor.

Air Pressure and Flow: How Do They Work Together?

Air pressure and flow have a unique relationship. When using a compressed air system, the goal is to supply the proper airflow at the correct pressure. It is imperative to know the minimum pressure needed to complete a task. A slow increase in pressure is always best so as not to waste energy.

As for airflow, it will take into consideration how often the task is completed. For example, let’s say you need to move something a short distance every hour with a compressed air system. This task will only require the use of a small compressor. However, if the task requires constant movement for several hours, then a larger compressor is required.

Overpressurization = High Energy Loss and Cost

When a facility does not understand flow vs. pressure and their system’s requirements, it can leave them open to many issues. Most often, a system will become overpressurized to consistently complete tasks. Many facilities will run their compressed air systems at full line pressure regulated only by the pressure switch on the compressor rather than use a pressure regulator.

When the psi is increased at the pump and not regulated directly after the accumulation tank, it increases energy costs and loss. Increased pressure also causes leaks. Some of the costliest leaks are those found near the compressor because that is where pressure is highest. Also, a system that is left pressurized when not in use can cause leaks.

Flow vs. Pressure: Recap

Understanding pressure and flow will ultimately help obtain the correct size of the compressor, reduce energy waste, improve the system’s productivity, and lower equipment and lifecycle costs.

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