Mechanical and Pneumatic Systems

What Mechanical and Pneumatic Systems covers

Mechanical and Pneumatic Systems is examined in Unit A2 1: Option B, Mechanical and Pneumatic Control Systems, one option of three. It covers hydraulics, system limitations and plant safety, torque, work, power and air consumption, vacuum handling, proximity sensors and 5/3 valves, sequential and cascade pneumatic circuits, cam profiles and follower displacement diagrams, gear geometry, pulley blocks and ratchets, Toggles, treadles, shafts and couplings, friction, brakes and clutches and bearings, lubrication and seals.

The 9 subtopics

Each one has its own page.

• Hydraulics, system limitations and plant safetyHydraulics against pneumatics, limits of pneumatic, hydraulic and mechanical systems, Pascal's principle with a worked press, governors, soft-start and dump valves, two-hand controls and interlocks.Open →
• Torque, work, power and air consumptionTorque, work and power with worked calculations, the effect of gearing on torque, potential and kinetic energy, and cylinder air consumption and free air conversion.Open →
• Vacuum handling, proximity sensors and 5/3 valvesVacuum cups and the force they hold with a worked example, safety factors, inductive, capacitive and reflex proximity sensors, and closed-centre and exhaust-centre 5/3 valves.Open →
• Sequential and cascade pneumatic circuitsSequence notation, feedback in sequential circuits, signal conflict and one-way trip valves, the cascade method and grouping rules with worked sequences, and programmable logic controllers.Open →
• Cam profiles and follower displacement diagramsDisplacement diagrams and base circles, uniform velocity, uniform acceleration and simple harmonic motion, offset followers, constructing profiles and worked timing examples.Open →
• Gear geometry, pulley blocks and ratchetsPitch circle diameter, module and centre distance with worked values, reverted gear trains, multiple pulley blocks with worked efficiency, and ratchets and pawls.Open →
• Toggles, treadles, shafts and couplingsToggle and treadle linkages, bell cranks with cylinders, shaft alignment, rigid and flexible couplings, universal and constant velocity joints, sliding and Oldham couplings.Open →
• Friction, brakes and clutchesStatic and dynamic friction and the coefficient of friction, cantilever, band, disc and drum brakes with a worked braking torque, and single plate, diaphragm, cone and centrifugal clutches.Open →
• Bearings, lubrication and sealsPlain, ball, roller, self-aligning, thrust and taper roller bearings, lubricants, viscosity, oil, grease and solid lubricants, O-rings, gaskets and rotary shaft seals.Open →

What you need to know

Answer each one before you reveal it.

Take Mechanical and Pneumatic Systems further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Static friction vs Dynamic friction

  Static friction: the resistance that must be overcome to start a stationary object sliding. Dynamic friction: the resistance acting on surfaces that are already sliding over each other.

• Disc brake vs Drum brake

  Disc brake: pads clamped by a caliper onto both faces of a rotating plate. Drum brake: shoes pushed outwards against the inside of a rotating cylinder.

• Universal joint vs Constant velocity joint

  Universal joint: a cross-shaped spider coupling whose output speed fluctuates when angled. Constant velocity joint: an angled drive coupling whose output speed never fluctuates.

Questions from this topic

Each one with the model answer underneath.

1. 1

   How does a hydraulic system differ from a pneumatic system?

   Model answer

   A hydraulic system transmits power through pressurised oil rather than compressed air. Oil is almost incompressible, so hydraulics give higher forces and more precise positioning.

2. 2

   Why can a pneumatic cylinder not hold a precise mid-stroke position under a changing load?

   Model answer

   Air is compressible, so the piston gives or bounces when the load changes. The movement is springy rather than rigid.

3. 3

   What limits the force available from a pneumatic system?

   Model answer

   Pneumatic systems work at fairly low pressures, typically below about 10 bar. Large forces therefore need very large cylinders, and hydraulics become the better choice.

4. 4

   Give two limitations of hydraulic systems.

   Model answer

   Oil leaks are messy and slippery, and can be a fire and environmental hazard. Hydraulic pumps, pipes and valves are also expensive and heavy.

5. 5

   Why are pneumatic systems often preferred in food and packaging plants?

   Model answer

   Leaking air is clean and does not contaminate products. Pneumatic parts are also cheap, fast-acting and able to stall safely under overload.

6. 6

   Why is compressed air an expensive form of energy?

   Model answer

   Much of the electrical energy used by a compressor is lost as heat. Leaks in pipes and fittings waste further energy all the time.

What is inside Levo

Six ways to work the same material.

Mechanical and Pneumatic Systems revision questions

What does Mechanical and Pneumatic Systems cover in CCEA A-Level Technology and Design?

9 subtopics: hydraulics, system limitations and plant safety, torque, work, power and air consumption, vacuum handling, proximity sensors and 5/3 valves, sequential and cascade pneumatic circuits, cam profiles and follower displacement diagrams, gear geometry, pulley blocks and ratchets, toggles, treadles, shafts and couplings, friction, brakes and clutches and bearings, lubrication and seals. Each one has its own page with questions and model answers.

How is Mechanical and Pneumatic Systems organised?

By the CCEA 8900 specification, subtopic by subtopic, so it matches the order you are taught it in.