# SA — Single acting

> Source: https://rodlesspneumatic.com/resource-center/pneumatic-glossary/sa/
> Language: en-US
> Category: Cylinder sizing

## Definition

Single acting: Air powers one direction and a spring or external load returns the actuator. Check spring force, fail position, and usable stroke. Read the applicable product data and technical standard before treating a catalog value as interchangeable.

## Key facts

- **Term:** SA
- **Full form:** Single acting
- **Selection effect:** Check spring force, fail position, and usable stroke.

## SA: definition and engineering context

Single acting. Air powers one direction and a spring or external load returns the actuator.

The term belongs to the cylinder sizing context. Its exact limits can depend on the cited standard, catalog convention, unit system, reference state, and component configuration.

## Why SA affects pneumatic selection

Check spring force, fail position, and usable stroke.

- Cushioning: Match kinetic energy and cycle speed; cushioning does not replace external stopping when limits are exceeded.
- A: Use the rod-side annular area for retract force, not the full bore area.
- Bore: Force rises with the square of bore diameter.
- Stroke: Confirm usable motion, overall length, and allowance for cushioning.

## How to evaluate SA in a catalog or replacement project

Read the value together with its unit, test basis, operating pressure, temperature, circuit state, and manufacturer definition.

For replacement work, compare the complete datasheet and drawing. A matching abbreviation or nominal size does not by itself prove functional or dimensional interchangeability.

- End-of-stroke cushioning: A method of reducing piston speed near an end cap.
- Effective piston area: Pressurized piston area used in the theoretical force calculation.
- Cylinder bore diameter: Inside diameter associated with piston area.
- Cylinder travel: Distance between the retracted and extended end positions.

## What to verify before selection

- Check spring force, fail position, and usable stroke.
- Match kinetic energy and cycle speed; cushioning does not replace external stopping when limits are exceeded.
- Use the rod-side annular area for retract force, not the full bore area.
- Force rises with the square of bore diameter.

## Common mistakes

- Treating SA as a universal definition without checking the manufacturer or standard context
- Mixing gauge and absolute values, incompatible units, or different reference conditions in one comparison
- Selecting a component from the term or nominal value alone without checking the complete operating point and drawing

## Frequently asked questions

### What does SA mean in pneumatics?

Single acting. Air powers one direction and a spring or external load returns the actuator.

### Why does SA matter when selecting a component?

Check spring force, fail position, and usable stroke.

### Can SA values be compared directly between catalogs?

Only after the unit, reference condition, test method, operating point, and manufacturer definition have been reconciled.

## Technical references

- [ISO 5598:2020](https://www.iso.org/standard/67985.html): Provides the international fluid-power vocabulary used to interpret pneumatic terminology.
- [ISO 3320:2013](https://www.iso.org/standard/61647.html): Specifies cylinder bore and piston-rod diameter conventions used in fluid-power data.