How are pneumatic time delays and automatic sequences of cylinders created?
The pneumatic time-delay circuit (reservoir and restrictor), flow-control of cylinder speed, and sequencing cylinders with limit valves.
A CCEA A-Level Technology and Design answer on the pneumatic time-delay circuit using a flow restrictor and reservoir, controlling cylinder speed with flow-control valves, and sequencing two or more cylinders automatically using limit valves.
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What this dot point is asking
CCEA expects you to describe the pneumatic time-delay circuit (restrictor plus reservoir), control cylinder speed with flow-control valves, and sequence two or more cylinders automatically using limit valves. The time delay and sequencing are core A2 pneumatic skills.
The answer
The pneumatic time-delay circuit
Adjusting the delay and controlling speed
Sequencing cylinders
Worked example: a timed, sequenced station
Examples in context
Example 1. Automatic door closer. A restrictor-and-reservoir arrangement delays and slows the closing so the door does not slam, the time-delay and flow-control ideas in a familiar product.
Example 2. Pick-and-place unit. Two or three cylinders extend and retract in sequence, each triggered by a limit valve as the previous reaches its stroke end, the textbook automatic sequence built from limit valves.
Try this
Q1. What two components create a pneumatic time delay? [2 marks]
- Cue. A flow-control (restrictor) valve and an air reservoir (which together pilot a valve once filled).
Q2. How would you make a pneumatic time delay longer? [1 mark]
- Cue. Close the flow restrictor more (slower fill) or use a larger reservoir.
Q3. What component detects that a cylinder has reached the end of its stroke in a sequencing circuit? [1 mark]
- Cue. A limit valve (a roller-operated 3/2 valve) at the stroke end.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA 20206 marksDescribe how a pneumatic time-delay circuit produces a delay, and explain how the length of the delay can be changed.Show worked answer →
A pneumatic time delay is made from a flow-control (restrictor) valve feeding an air reservoir that pilots a valve. When a signal arrives, air can only trickle through the restrictor to slowly fill the reservoir; the pilot valve does not switch until the reservoir pressure rises to the level needed to move the spool. The time taken to build that pressure is the delay.
So the sequence is: signal -> air bleeds slowly through the restrictor -> reservoir pressure builds -> at the threshold the pilot valve switches (delayed action).
The delay is changed by:
- Adjusting the flow restrictor (a needle valve): closing it more slows the air flow, so the reservoir fills more slowly and the delay is longer; opening it shortens the delay.
- Changing the reservoir volume: a larger reservoir takes longer to fill, lengthening the delay.
Markers reward the restrictor-fills-reservoir-which-pilots-a-valve mechanism, the delay = time to build pressure, and changing the delay by adjusting the restrictor (or the reservoir size).
CCEA 20214 marksExplain how two cylinders, A and B, can be made to operate in sequence (A extends, then B extends) using limit valves.Show worked answer →
To sequence the cylinders, the completion of one movement triggers the next, using limit valves (roller-operated 3/2 valves) placed at the ends of the strokes:
- A start signal pilots cylinder A's directional valve, so A extends.
- When A reaches the end of its stroke, it presses a limit valve (a+) positioned there. This limit valve sends a pilot signal to cylinder B's directional valve.
- That pilot makes cylinder B extend.
So A's completed stroke automatically starts B, giving the sequence A+ then B+ without the operator. Further limit valves can continue the sequence (for example B+ triggers A- and so on).
Markers want the use of limit valves at stroke ends, A's limit valve piloting B's valve, and the resulting automatic A-then-B sequence.
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Sources & how we know this
- CCEA GCE Technology and Design specification — CCEA (2016)