What is the purpose of a restrictor in pneumatic systems (independent or dependent)?

• A. Speed control
• B. Pressure relief
• C. Temperature control
• D. Flow measurement

Answer: (A)

In pneumatic systems, a restrictor is used to control how fast air can move through a line, which translates directly into controlling the speed of an actuator like a cylinder. By throttling the flow either in the supply path or the exhaust path, a restrictor slows down the extension or retraction of the piston, giving smoother starts and stops and reducing shocks to the mechanical system.

Independent restrictors affect flow in one direction, so you can set different speeds for extending versus retracting when paired with other valve elements. Dependent (flow-control) devices throttle in both directions, often using a check mechanism to manage the return flow as well, giving balanced or matched speeds.

This purpose—governing the rate of air flow to achieve desired actuator speed and smooth operation—fits the idea of speed control best, while the other options describe different functions (pressure relief, temperature control, flow measurement) that aren’t the primary role of a restrictor.