Pneumatic systems: compressed air, cylinders and valves, single and double acting cylinders, and the force a cylinder produces.

What this dot point is asking

CCEA Unit 3 expects you to understand pneumatic systems: how compressed air drives cylinders through valves, the difference between single and double acting cylinders, and how to calculate the force a cylinder produces from pressure and area.

The answer

What pneumatics is

Cylinders and valves

A cylinder converts air pressure into a pushing or pulling force on its piston rod. Valves control when and where the air flows, so they switch the cylinder on, off or change its direction. A typical system has a compressor to make the compressed air, a reservoir (receiver) to store it, a filter and regulator to clean it and set the pressure, directional control valves to route the air, and the cylinder as the actuator. Pneumatics is widely used in factories because compressed air is cheap to produce, the parts are simple and robust, and the systems are clean and safe to use.

The force a cylinder produces

The force from a cylinder comes from pressure acting on the piston area. Since pressure is force per area, $p = \dfrac{F}{A}$, rearranging gives:

where $F$ is the force in newtons, $p$ the air pressure in pascals and $A$ the piston area in square metres. A larger piston or higher pressure gives more force.

Worked example: a pneumatic force calculation

Examples in context

Example 1. A factory clamp

A single acting cylinder clamps a workpiece when air is applied and a spring releases it when the air is cut, a simple one-direction action.

Example 2. An automatic door or press

A double acting cylinder drives the door or ram firmly both ways, because air powers both the out and return strokes.

Example 3. Sizing a cylinder

An engineer chooses the piston area and air pressure so that $F = pA$ gives enough force to move the load, increasing area or pressure if more force is needed.

The pattern is that pneumatics turns stored air pressure into a controllable push or pull, with the force set by pressure times piston area and the motion set by the valve and cylinder type.

Try this

Q1. What does a pneumatic system use to do work? [1 mark]

• Cue. Compressed air.

Q2. State the difference between a single and a double acting cylinder. [2 marks]

• Cue. Single acting: air pushes one way, spring returns it. Double acting: air powers the piston both out and back.

Q3. A piston of area $0.0010\ \text{m}^2$ runs at $300000\ \text{Pa}$. Find the force. [2 marks]

• Cue. $F = pA = 300000 \times 0.0010 = 300\ \text{N}$.