Key term
CCEA A-Level Technology and Design 8900
Material Selection and Wood
Metals
Plastics
Composite and Emerging Materials
Processing Materials
Product Analysis and Design Communication
Design for Manufacture, Quality and Safety
Electronic Control SystemsOption A
Topic overviewControl systems, feedback and electronics safetyResistors, Ohm's law and power ratingsCapacitors and RC timingPotential dividers, sensors and comparatorsSwitches, pull-up and pull-down resistorsOutput devices and LEDsTransistors, Darlington pairs and thyristorsLogic gates, truth tables and flip-flops555 monostable and astable timers
Microelectronic Control SystemsOption A
Topic overviewMicrocontroller systems, ADCs and DACsStrain gauges and bridge circuitsOptical switches, encoded discs and Schmitt triggersOp-amp amplifiers and gainZener diodes and voltage regulatorsKarnaugh maps and binary countersSeven-segment, LCD and dot matrix displaysPIC flowcharts and programmingDC motors, stepper motors and driver circuits
Mechanical and Pneumatic ComponentsOption B
Topic overviewOpen and closed loop mechanical and pneumatic controlSafe working with compressed air and mechanismsLevers, linkages and momentsGear types and gear trainsPulleys, belts, chains and shaft fixingsCams, cranks and converting motionCompressed air supply and pneumatic valvesCylinders, shuttle valves, restrictors and reservoirsPneumatic circuits for logic, timing and speed control
Mechanical and Pneumatic SystemsOption B
Topic overviewHydraulics, system limitations and plant safetyTorque, work, power and air consumptionVacuum handling, proximity sensors and 5/3 valvesSequential and cascade pneumatic circuitsCam profiles and follower displacement diagramsGear geometry, pulley blocks and ratchetsToggles, treadles, shafts and couplingsFriction, brakes and clutchesBearings, lubrication and seals
Designing and Manufacturing ProductsOption C
Topic overviewResearch, questionnaires and specificationsIdea generation, critiques and computer simulationManufacturing planning and product evaluationCFRP, GRP, Kevlar and tungsten carbideSmart materials, nanotechnology and biophotovoltaicsIsometric, perspective and assembly drawingLaminating, steam bending, cutting and printing processesRisk assessment and product safety lawScales of production, JIT and cell productionQuality assurance, ISO 9001 and continuous improvementDesign influences and intellectual property rights
Product Design in Industry and SocietyOption C
Topic overviewLife-cycle environmental impact and climate changeThe 6Rs, waste and environmental legislationSustainable metals, plastics and degradable polymersProduct life cycles, consumer types and relaunchesCAD, CAM, 3D scanning and quick-change mouldingMarket pull, technology push and market strategyPrice, place and promotionJigs, fixtures and ICT in quality controlDesign for maintenance, inclusion and scale productionRendering, typography and presentationDyson, Baylis, Memphis and Apple
Product Development
Product and System Design and Manufacture
Mechanical and Pneumatic Systems
Hydraulics, system limitations and plant safety
- 3 things to know
- A2 1
Overview
Hydraulics 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.
What you need to know
Answer each one before you reveal it.
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Key term
Why can a pneumatic cylinder not hold a precise mid-stroke position under a changing load?
Key term
What limits the force available from a pneumatic system?
Questions from this subtopic
Each one with the model answer underneath.
- 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
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
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
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
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
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.
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