Why Correctly Sizing Pneumatic Components is Important

The most important function in the design of a pneumatic system is to correctly size the pneumatic components. Too often, components are chosen primarily because of what is readily available at the time or because the component is already currently being used throughout a facility. Improperly sourced components can result in an inefficient system leading to decreased productivity and increased cycle times, along with increased component and energy costs associated with compressed air.

One of the key factors in determining how to properly size for performance and efficiency includes Valve selection.

Valve Selection

Calculating the Cv required is the best method for selecting a valve. Cv, or flow coefficient, is a way to measure a components ability to flow air. The higher the Cv, the more the valve will flow. Most valve manufacturers will list their Cv ratings, making it relatively easy to compare the many different valves available. Valves today are reduced in size while flow ratings are increased, so you can no longer judge the valve by its port size.

The following equation can be used to determine the Cv required for your application.

Cv = (Area x Stroke x C) ÷ (Time x 29).

Area = π x radius squared, also the same as power factor in the cylinder sizing chart.

Stroke = Cylinder travel in inches

C = Constant (see table)

Time = in seconds

* “C” constant based in a 5 PSI pressure drop for most normal applications

Example:  2” bore actuator with a 6” stroke cycling 60 times a minute at 80 psi. Cv = (3.1 x 12 x .3072) ÷ (1 x 29) = 11.4278 ÷ 29 = .394 Cv. Therefore, our valve selection will need a minimum Cv of .394.

Optimizing performance, reducing component costs and reduced energy costs associated with compressed air are all easily achieved if time is taken to properly size out air components within the early planning stages of your design. Click the link below for additional details and sizing charts to help guide you in taking the necessary steps to ensure a properly designed system.

Sizing Pneumatic Components


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