Pneumatic Circuit Design Requirements

1. Engineering answer: a circuit specification describes behaviour, not just components

Pneumatic circuit design requirements translate a machine task into a documented agreement about motion, pressure, airflow, sequence, feedback, abnormal conditions and acceptance. A useful specification explains the required result at the mechanism and identifies the evidence needed before each subsequent action. The drawing, valve selection and control program must all implement that same agreement.

A list containing a cylinder, directional valve, regulator and two sensors is not sufficient. It does not say whether the cylinder may move during pressurisation, what confirms that a clamp has secured the workpiece, whether a process may continue when pressure falls, or how a stopped sequence is recovered. These omissions often become commissioning changes because the components can be connected while the intended behaviour remains ambiguous.

The outcome is a circuit specification with identifiable states, transition conditions, fault responses, interface responsibilities and verification records.

The governing question is not simply “Which valve operates this cylinder?” It is “Which verified pneumatic and control arrangement delivers the required machine behaviour across the agreed operating conditions?” Component selection follows that answer rather than substituting for it.

2. The decision owns

This separation matters because a requirement and a design solution are different objects. “Maintain the workpiece in its approved supported position during the specified interruption” is a functional requirement. “Install a particular valve” is a proposed implementation that needs evidence. A catalogue description cannot close the requirement unless its operating conditions and system integration match the actual task.

Use this page for a new machine enquiry, a retrofit specification, a repeat-machine standard, a fault investigation that reveals undocumented behaviour, or a supplier design review. Preserve existing drawings and software revisions when extending a machine. New requirements should identify what changed rather than implying that an earlier accepted arrangement never existed.

All teaching states and numerical cases in this document are original explanatory additions. They are not recovered customer settings, tested machine sequences or manufacturer-approved circuits. The attached bookmark collection identifies useful resource locations but does not contain the complete design of the machine considered here. [S4; N1]

3. Turn a verbal request into a measurable requirement

Start with the action at the workpiece: locate, clamp, push, lift, index, release, divert or position. Define the reference point, travel, orientation, load range, permitted contact force, acceptable movement time and evidence of completion. “Cylinder extends quickly” should become a measurable requirement for an identified mechanism under stated load and supply conditions.

Give each requirement a stable identifier. Separate the requirement text from its source, rationale, proposed implementation and acceptance method. This prevents a supplier's chosen bore size or a programmer's provisional timer from becoming an undocumented customer requirement. A changed component may still meet the same requirement, while an unchanged component may fail after the duty changes.

Avoid combining independent obligations in one sentence. Movement time, end-position confirmation, pressure retention and restart behaviour deserve separate records because they may need different evidence. A single test showing that a rod reached its end switch cannot automatically prove all four. Identify mandatory requirements separately from preferences such as a preferred supplier family or a convenient connection arrangement.

A strong specification also states what has not been decided. Unknown load, missing pressure limits, unresolved retention behaviour and unconfirmed interfaces should have named owners and due points. Recording an unresolved requirement is more useful than filling the field with a plausible number that later appears authoritative.

For a retrofit, record the observed symptom separately from the desired outcome. “Intermittent failure to clamp after lunch” is evidence of a problem, not a design pressure. Capture the circumstances, then define the measurable service the corrected circuit must deliver. [S1, S2; N1]

4. Establish the circuit boundary and utility contract

Define where the plant's responsibility ends and the machine's begins. The boundary may be the machine isolation inlet, a connection after local treatment, or another agreed terminal point. Mark it on the drawing and name the pressure and quality measurement locations. Include the exhaust route and any separate pilot supply; they are interfaces, not invisible background conditions.

The specification should distinguish the lowest available dynamic pressure from the normal target and the maximum permitted pressure of individual components. It should also distinguish a sustained flow allocation from a short event. A header rating cannot establish either the pressure at the manifold during peak demand or the suitability of the final tubing.

Use conditional requirements where appropriate. A circuit without an external pilot supply should say “not applicable” with a reason, rather than pretending an unmeasured pilot pressure is zero. The same discipline applies to vacuum interfaces, auxiliary receivers and shared exhaust arrangements.

5. Define motion and load requirements before selecting actuator size

Record the complete motion, not only the longest stroke. Include approach, working travel, dwell, return, deceleration, end stop and any intermediate position. Identify where the mechanism contacts a workpiece and where load changes abruptly. A cylinder that pushes freely through most of its travel may encounter its highest resistance over only a short working interval.

State whether the load is horizontal, vertical, inclined, overhauling or supported by an external mechanism. Include changes caused by tooling, product variants and moving fixtures. The piston rod should not silently become the assumed guide or structural support for an externally applied load; those functions need a defined mechanical arrangement.

At the requirement stage, specify the force needed at the actual working interface and any maximum force that would damage the product. Retain leverage, linkage geometry and friction assumptions for later sizing. If force must be known rather than merely bounded by pressure and geometry, identify the required measurement or validated relationship. A pressure switch alone does not measure contact force throughout an arbitrary mechanism. [S1; N1]

Specify whether the movement needs end-to-end operation, repeatable intermediate positioning or controlled motion against a varying load. These requirements may lead to different pneumatic, electric, hydraulic or mechanical solutions.

Finally, define acceptable failure behaviour at each phase. A return action that is harmless when the fixture is empty may be unacceptable while it supports a workpiece. “Retract on fault” is therefore incomplete unless the fault, machine state and resulting consequences are specified.

6. Describe operating modes separately from sequence steps

Operating mode answers who may command the machine and under what restrictions. Sequence state answers what the machine is doing now. Automatic production, supervised setup, maintenance and recovery are modes; extending, dwelling and returning are states. Combining them in one unstructured list makes transitions difficult to review.

Define how modes are selected, who has authority, what happens to an active cycle when the mode changes, and whether any commands remain active. A change from automatic to setup should not silently retain a stale movement request.

For automatic operation, identify cycle-start conditions, normal completion, controlled interruption and the point at which the next cycle may be accepted. For setup, specify permitted movements, any hold-to-run requirement established by the responsible designer, speed or force limitations where applicable, visibility and supervision. The website example cannot assign those protective measures to a real machine.

For recovery, define how actual actuator positions, workpiece condition, pressure and retained process state are reconciled. Recovery is not simply replaying the next output from the interrupted automatic cycle. It may require a different supervised procedure with its own entry conditions.

Describe normal stop, emergency response and maintenance isolation independently. Their purposes and evidence differ. The circuit requirement should reference the responsible safety assessment where a function protects people; an ordinary sequence table must not imply that its software conditions alone provide that protection.

7. Build state records and transition records that can be tested

A state record should describe the intended physical condition, permitted commands, required feedback and conditions that must remain true. A transition record should identify the event, prerequisites, destination and response when prerequisites are absent. Keeping both records prevents the next step from depending on an unexplained arrow.

A timer can limit how long the controller waits for evidence. It does not create the evidence. Similarly, a position switch proves only its documented detection condition; it may not prove force, clearance or successful processing. State the actual meaning of every confirmation.

Define priority when events occur together. An invalid measurement or loss of a required permissive must not disappear because a completion event arrived in the same scan or reporting interval. Exact execution priority belongs in the implementation specification and its tests. The following teaching sequence illustrates the record structure, not a safety-program implementation. [N1]

8. Worked example 1: a clamp-and-transfer sequence with explicit proof

Consider a fictional guarded transfer fixture with two horizontal actuators. A locates a workpiece against a supported nest; B advances a transfer member. The chosen teaching sequence is A extend, B extend, B retract, A retract. “Extend” and “retract” describe functional movements only. They do not define solenoid wiring, valve port connections or a protective response.

Assume the machine designer has separately established the guarding, mechanical support and safety functions. The purpose here is to show why B's advance requires more than an A-extend command. In this teaching case, the transition requires an accepted location signal and an accepted process-pressure condition. A real fixture may require different or additional evidence.

Suppose A reaches its switch but the required process-pressure signal is invalid. S30 does not advance to S40. The correct record is “position observed; pressure prerequisite unresolved,” not “A complete.” If B fails to return, a subsequent timer expiry does not authorise A release.

If pressure is restored after a fault, the incident remains in S90 until the defined review and reset conditions are satisfied. The proposed reset destination is S10. A new production start follows only after preparation and readiness. This teaching convention prevents automatic sequence continuation; actual actuator behaviour on loss or restoration of energy must still be engineered physically. [N1]

9. Define architecture by function before creating the bill of materials

Separate supply isolation, air preparation, pressure control, distribution, directional control, speed control, feedback and any safety-related functions. A combined valve island can implement several functions, but their requirements and interfaces should remain distinguishable. Otherwise replacing one assembly may change functions that procurement did not realise were included.

Describe the boundaries between pressure zones. Identify which devices share a manifold supply, which have separate regulators, which exhaust together and whether a pilot circuit remains energised when the main circuit is isolated. Record stored volumes and any one-way elements that can prevent pressure from leaving a downstream section.

Specify the physical arrangement only as far as the requirement is known. A short valve-to-cylinder connection may be desirable for response, but the final location must also consider access, moving mass, environmental exposure and maintenance. Do not select a valve location solely from a schematic that has no physical lengths.

Create a functional responsibility matrix before the equipment list. The pneumatic designer owns the flow path and component operating conditions; the mechanical designer owns load support and motion geometry; the controls designer owns command and feedback implementation; the responsible safety discipline owns protective-function requirements and validation. Procurement and installation must preserve the resulting configuration.

This is especially important during substitutions. Matching thread size and coil voltage does not establish equivalence. A replacement can change normal position, pilot arrangement, exhaust routing, response, leakage behaviour or manual override. The specification should say which attributes are controlled and which changes require review.

10. Interpret directional-valve states through actual port connections

A valve designation identifies a family of functions, not the complete machine behaviour. Read the exact symbol, actuation method, return mechanism, pilot supply and manufacturer description. Document each commanded and uncommanded condition rather than assuming that “off” means no motion.

The force on an unequal-area cylinder depends on both chamber pressures and the external load. Port blocking, port exhausting and applying pressure to both ports therefore need different physical interpretations. A centre-position label is not a substitute for that analysis. [S1; N2]

SMC's common precautions specifically warn that air compressibility and leakage limit intermediate stopping and long-duration holding, and that shared exhaust backpressure can affect actuators. They also call for consideration of residual pressure.

11. Include pilot conditions, switching and initial pressurisation

Some directional valves depend on pilot pressure to shift or return as documented. The specification must therefore identify the actual pilot arrangement and its permissible conditions. Main supply pressure, pilot pressure and electrical command are separate inputs. A command may be present while the pressure needed for the intended valve action is not. Confirm this against the exact selected valve. [R1; N1]

Define behaviour while the machine is initially pressurised. Which chambers can receive pressure first? What positions can valves occupy before the controller is ready? Is an external pilot supplied earlier or later than the main manifold? Are retained manual overrides or stored commands possible? These questions belong in the initial-condition review, not only in fault troubleshooting.

Soft pressurisation can change the rate at which a circuit becomes available, but it does not by itself establish safe startup. Festo's guidance distinguishes soft-start functions from the complete safety solution and calls attention to unintended manual-override operation. Use the selected equipment's operating data and the machine's approved design for actual implementation. [R2]

Record switching-time information with its test conditions. A valve's electrical response is not the complete actuator movement time. Include controller processing, communication, output response, pilot behaviour, chamber pressure development, travel and feedback confirmation when specifying an end-to-end response.

Where delays or pressure thresholds are proposed, record their origin and acceptance evidence. Do not copy a delay from an unrelated machine or use a longer timer to conceal incomplete movement. The appropriate requirement may be “establish readiness from valid feedback,” with a separate maximum waiting time for diagnostic purposes.

12. Specify pressure and force at the correct points

The pressure contract should extend from the machine inlet to the chamber or consumer relevant to the requirement. A regulator's no-flow setting is not evidence of pressure during movement. Include losses across the filter, regulator, isolation device, directional valve, tubing, fittings and exhaust path where they affect operation.

Keep the required pressure at the actuator separate from the maximum permitted component pressure. A higher source setting can improve apparent force while exceeding another component's allowable condition or unnecessarily increasing other air uses. The requirement should identify the responsible person and evidence for any setpoint change.

For a single-rod cylinder extending in a common atmospheric environment, an explanatory force balance is:

F_available = p_cap,g × A_piston − p_rod,g × A_annulus − F_friction.

Use pascals and square metres for newtons. Define whether the external working load and acceleration are compared separately or included in another explicitly named term. Do not subtract the same resistance twice. This expression is a simplified calculation, not proof of motion, buckling resistance, cushioning performance or safe retention. [S1; N2]

Specify the envelope across which the force requirement applies: lowest permitted supply, credible exhaust backpressure, relevant temperature and the actual load condition. The required result may be a minimum force, a bounded force range or a position/time outcome. These are different acceptance requirements and should not be collapsed into “six-bar air.”

13. Specify response using flow, volume and the complete exhaust path

Average air consumption is useful for utility planning, but the circuit must deliver and release air quickly enough during individual movements. Record powered-stroke duration, dwell, return time, repetitions and simultaneous actions. The short-period flow requirement can greatly exceed the average even when no additional air is consumed per cycle.

Require valve and regulator flow information at applicable inlet/outlet conditions and on a declared reporting basis. Cv, sonic conductance, nominal flow and port size are not interchangeable descriptions. A data-sheet value at one pressure drop cannot be treated as a constant available flow throughout chamber filling. Final selection belongs to an appropriate dynamic method and supplier data.

Include tube internal diameter, length, fittings, flow-control direction, exhaust silencers and any common manifold. The exhaust side can change both motion speed and opposing chamber pressure. A quieter silencer or convenient remote exhaust can alter response; identify those attributes as controlled requirements instead of unrecorded installation details.

Meter-in, meter-out and other speed-control arrangements need application-specific assessment. Avoid a universal instruction based only on actuator direction. Load behaviour, startup, compressibility, cushioning and failure response affect the choice. State the required motion, then ask the designer to justify the selected arrangement.

A simple reference-volume-per-stroke divided by stroke time can expose the scale of a demand event. It cannot establish the full pressure trajectory or the final valve size. Section 22 uses this screen while retaining its limitations. Do not convert that average-over-stroke flow into a claimed instantaneous peak.

14. Define air quality, lubrication and environmental requirements

Record the air quality required by each component and by the process exposed to its exhaust or working air. These may be different boundaries. A cylinder driving a fixture, a product-contact blow-off and a vacuum ejector may share a machine but need different contamination controls. The supply specification should preserve the most relevant requirement at each endpoint rather than assuming one generic preparation label resolves all uses.

Specify filtration and regulation separately from lubrication. A lubricator is not mandatory because an assembly is called an FRL. Conversely, equipment requiring a documented lubrication regime should not lose that provision through a generic “oil-free operation” statement. Record the exact manufacturer's condition and the consequences of changing an established arrangement.

Include ambient and media temperature, washdown, dust, corrosion, vibration, mounting orientation and exposure of exhaust outlets. Material compatibility, seals, tubing and connectors should follow the application and selected component documentation. Do not invent a universal pneumatic cleanliness class or temperature range.

Identify the responsibility for drainage and for preventing process fluids from entering the pneumatic network. Cross-connections, temporary hoses and maintenance substitutions can change the contamination path.

The functional specification should also preserve pressure-loss consequences of treatment. Removing required filtration to improve motion is not a complete solution. Equally, unnecessarily restrictive treatment can create a pressure problem that is mistakenly attributed to actuator sizing.

15. Define signals by meaning, not by convenient names

Each input needs a physical meaning, location, normal interpretation, failure interpretation and data-quality rule. Each output needs an identified controlled function, electrical interface and documented behaviour when the command or its supply is lost. A list of names such as “A_OK” and “AIR_OK” is insufficient unless the reader can determine what each signal actually proves.

Record active-high/active-low logic, signal type, scaling, timeout or age limit, debounce where justified and contradictory-state handling. A disconnected analogue channel must not be interpreted as a valid zero unless that behaviour is explicitly and correctly defined. A stuck position switch requires a different investigation from an actuator that genuinely cannot reach the position. [N1]

Position and pressure evidence should remain independently visible. This supports both commissioning and later diagnosis. Where safety functions require diagnostic coverage, redundancy or particular architectures, those requirements must come from the responsible safety design, not from the naming convention used in this table.

16. Write abnormal-condition requirements before commissioning

An abnormal-condition matrix records the initiating event, the machine states in which it matters, the required physical response, the evidence of completion and the permitted recovery. A single “fault = all outputs off” sentence is not sufficient for a circuit containing retained pressure, spring returns, gravity loads or bistable valves.

Distinguish process abnormalities from protective demands. A process timeout may inhibit subsequent production, while a safety demand invokes a separately specified safety function. Their physical outputs and verification may interact, but their purposes must not be confused.

Prioritise credible simultaneous conditions. Power loss can be accompanied by loss of pilot air or by a stopped cooling/service system. The requirements should identify which combinations need analysis rather than assuming that every fault occurs alone under ideal supply.

17. Separate stopping, resetting, restarting and maintenance isolation

A normal stop ends or interrupts production according to an agreed rule. Reset acknowledges an eligible condition after the cause has been addressed. Restart authorises a new operating action. Isolation establishes the conditions needed for the specified intervention. None of these words should be used as an automatic synonym for the others.

It returns the process to preparation or readiness after the required conditions are checked. Whether a reset can be accepted, which evidence must be valid and whether a new start edge is required are explicit requirements. This is a design convention for the examples, not a substitute for a machine-specific safety function. [N1]

Festo's pneumatic-stopping guidance explains that trapped compressed air can remain after stopping, that movement can continue during stopping, and that restart conditions influence subsequent motion. The requirement implication is to name the physical energy and load state rather than relying on the word “stopped.” [R3]

Identify every area where pressure can remain after the main inlet is isolated: blocked cylinder ports, check-valve sections, receivers, pilot circuits and independent connections. The responsible procedure must establish how those conditions are verified and made suitable for the intended work. This page does not instruct personnel to loosen connections as a pressure test.

Also consider mechanical, electrical, spring and gravitational energy. An upstream gauge at zero cannot prove that all hazards are removed. The machine-specific isolation and support arrangements remain controlled by competent personnel and the site's approved procedures. [S1; R1]

18. Treat holding, load retention and vacuum release as separate functions

A command to stop moving does not establish that a load will remain where it is. Define retention direction, duration, permissible displacement, external forces and the condition of the energy supply. A fixture that only holds a supported workpiece has a different duty from a vertical axis or a suspended vacuum-held load. The same valve symbol cannot determine the appropriate response for all of them.

Do not use a closed-centre directional valve as an assumed indefinitely leak-tight lock. Component leakage, gas compressibility and changing loads must be considered. Likewise, a mechanical holding component has its own intended use, operating conditions and release requirements; its name alone does not prove that it can brake a moving load. The selected implementation needs its own evidence. [R1; N1]

For vacuum circuits, separate the holding requirement from evacuation time, leak tolerance and commanded release. A check valve may preserve a local condition temporarily, but retention time depends on the whole system and workpiece. Blow-off release can create motion or disturb adjacent workpieces. Record when release is allowed and how its completion is verified.

For a load that must remain supported during loss of utility, identify the responsible mechanical and safety design. The requirement should specify the outcome and verification, not offer a universal circuit retrofit. Maintenance access must not depend on an unverified trapped-air or vacuum condition.

These requirements should be resolved before automatic operation is approved. Leaving them as “to be checked on site” transfers a fundamental design question into a much less controlled commissioning situation.

19. Make the drawing, component schedule and change record agree

The schematic should identify controlled components, ports, pressure zones, pilot paths, exhaust paths, test points, isolation boundaries and relevant retained volumes. State the drawing convention and revision. Where a symbol or port label comes from the manufacturer, preserve the applicable legend instead of assuming that a letter has the same meaning on every product.

The component schedule should connect each drawing tag to the exact configuration: valve function, actuation, pilot arrangement, rated conditions, flow data, coil details, connectors and permitted alternatives. The controls signal list should resolve to the same tags. A correctly written requirement is not implemented if the installed valve differs from the drawing or the output address operates another device.

Record tubing internal diameter and controlled maximum lengths where response depends on them. Include exhaust components and fittings rather than treating them as unimportant installation consumables. The supplied point-of-use material explicitly identifies valves, tubing, hoses, couplings and exhaust as contributors to performance.

For a change, record as-found configuration, reason, proposed replacement, affected requirements, updated drawing/software versions and retest scope. Do not overwrite the earlier accepted baseline. A maintenance substitution can require rechecking movement time, pressure margin, loss-of-energy behaviour or sample quality even when production appears normal afterward.

A practical handover should let a person unfamiliar with the installation trace one requirement through the state description, component tag, control signal and witnessed test. If that chain cannot be followed, add the missing relationship rather than another decorative approval box.

20. Commission against requirements, not only successful movement

Prepare acceptance cases before the machine is energised for commissioning. Each case should identify the requirement, approved starting condition, permitted test method, measured evidence, acceptance basis and responsible reviewer. Testing must remain within the approved machine and site procedure; a website checklist is not permission to create a hazardous fault on live equipment.

Begin with configuration verification and appropriate offline review. Then use the agreed controlled tests to establish normal sequence, pressure and motion performance. Separate arithmetic or document checks from physical tests. The fact that a state table contains no missing fields does not demonstrate that a valve shifts correctly or that an isolation function works. [N1]

Close failures individually and repeat the affected cases after correction. Retain rejected results and superseded configurations. A passing retest does not erase the defect history; it establishes the outcome for the as-left configuration under the tested conditions.

21. Worked example 2: pressure at the chamber and exhaust backpressure

A fictional horizontal cylinder has an 80 mm bore and a 25 mm rod. The simplified requirement is at least 2,500 N available for the external working load after an assumed 180 N friction allowance, with acceleration excluded from this illustration. During extension, measured chamber pressures are 5.6 bar gauge on the cap side and 0.8 bar gauge on the rod side. Both use the same surrounding atmospheric reference.

A_piston = π × 0.080² / 4 = 0.005026548246 m².

A_annulus = π × (0.080² − 0.025²) / 4 = 0.004535674394 m².

Cap-side force contribution = 560,000 × 0.005026548246 = 2,814.867018 N.

Opposing rod-side contribution = 80,000 × 0.004535674394 = 362.853951 N.

Available force after the stated friction allowance = 2,814.867018 − 362.853951 − 180 = 2,272.013066 N.

The shortfall against the fictional 2,500 N working requirement is 227.986934 N. Ignoring the exhaust-side contribution would give 2,634.867018 N and would incorrectly suggest that this simplified force requirement is met. The comparison does not prove that the exhaust hardware is defective; the data establish an opposing-pressure contribution that the circuit designer must investigate.

Under the same assumptions, the cap-side pressure required algebraically is (2,500 + 180 + 362.853951) / (0.005026548246 × 100,000) = approximately 6.053566 bar gauge. This is not an instruction to raise the regulator. The design must consider component limits, load evidence, exhaust conditions and motion requirements before any change.

No real component is selected and no safety margin is invented by this example. [N2]

22. Worked example 3: low average consumption does not establish fast response

A fictional double-acting cylinder has a 50 mm bore, 20 mm rod and 200 mm stroke. Assume both powered strokes fill to 6 bar gauge, local atmospheric pressure and reference pressure are both 1 bar absolute, temperatures are equal and compressibility factors are one. Leakage, dead volumes, pressure dynamics and cushioning are excluded. These assumptions make the example reproducible, not a final consumption guarantee.

The extension swept volume is 0.392699082 L and the retraction swept volume is 0.329867229 L. At the stated pressure ratio of 7, the reference-air quantities are 2.748893572 L per extension and 2.309070600 L per retraction. A complete cycle therefore uses 5.057964172 reference litres in this simplified model.

At six complete cycles per minute, average reference flow is 30.347785034 L/min. However, completing the extension in 0.25 s corresponds to a volume-over-time screen of 659.734457254 L/min over that stroke. This is an average over the stated stroke interval, not the true instantaneous peak and not the flow a particular valve will maintain throughout filling.

Two identical cylinders extending in the same 0.25 s interval would produce a summed screening value of 1,319.468914508 L/min during that overlap. Their combined cycle-average demand at the stated rates remains 60.695570067 L/min. Staggering the strokes could change simultaneous demand without changing the ideal air quantity per completed cycle, subject to the actual process and approved sequence.

The requirement implication is to record both consumption and movement-time obligations. Selecting a regulator, manifold or tube from the 30.35 L/min average alone would not address the fast-stroke question. Final response requires a suitable dynamic assessment and component data; the example does not calculate Cv or certify a valve size. [S5; N2]

23. Worked example 4: timing evidence, equality and reset behaviour

Consider the same fictional locate-and-transfer concept used in Section 8. A position indication is first observed at 0.60 s after the locate command. The required process-pressure indication is first observed at 0.78 s. The proposed process rule requires both valid indications to remain true together for 0.10 s before transfer is permitted. The maximum locate waiting time is 1.00 s.

The earliest qualifying time is max(0.60, 0.78) + 0.10 = 0.88 s, leaving 0.12 s before the defined waiting limit. Using position alone would permit transfer at 0.60 s, which is 0.28 s earlier than this particular evidence rule permits. These numbers illustrate a requirements convention; they are not recommended machine timer settings.

Now assume the pressure indication becomes invalid at 0.84 s and becomes valid again at 0.90 s. If both indications then remain continuously true, the qualifying time becomes 1.00 s. The rule must define whether equality is accepted. For this teaching case, confirmation at or before 1.00 s is accepted, provided no higher-priority fault or invalid condition is present at that instant. Confirmation later than 1.00 s is not accepted.

An implementation must account for its actual timestamp resolution and evaluation order. It cannot infer a continuous 0.10 s proof interval from two unrelated snapshots with an unobserved gap. Likewise, clock correction must be documented rather than applied until the graph looks satisfactory.

If the locate step times out, subsequent restoration of pressure does not continue the transfer. The proposed process record stays in fault review; an eligible deliberate reset returns to preparation. A fresh production start is accepted only from readiness. This tests the written sequence convention, not the physical adequacy of a protective circuit. [N1, N2]

24. Editable worksheet A — circuit requirement register

Use one record for each independently verifiable requirement. Duplicate the rows as necessary. Keep source text and measured evidence separate from proposed settings. Bracketed entries are fields to complete, not approved operating values.

A completed example entry could require the fictional B transfer to remain inhibited until the agreed A location and pressure evidence is valid. Its acceptance case would challenge missing and contradictory prerequisites under an approved test arrangement. The actual fault-output mapping would remain linked to the machine's separately approved design.

Review requirement completeness before requesting quotations. Missing load and state behaviour can otherwise reappear as supplier exclusions, while unrecorded timing assumptions become commissioning disputes. The register gives each unresolved item a place and an owner without inventing the answer.

25. Editable worksheet B — state, transition and abnormal-condition register

Create separate records for normal states and exceptional transitions. A state should remain identifiable after software step numbers change. Store functional actions separately from the eventual hardware addresses so that a wiring change does not silently change the requirement.

Review every path into automatic movement. Check startup, return from setup, recovery after air loss, controller restart, manual-override removal and fault reset. The register should expose any path that bypasses required evidence.

For an unresolved physical response, use an explicit status such as “DESIGN RESPONSE REQUIRED.” Do not populate a convenient “all off” command to make the table look complete. The absence of an approved response is an engineering action, not a software formatting problem.

26. Editable worksheet C — verification and change closeout

This record links evidence to the exact as-tested configuration. It is suitable for requirements review and later commissioning records, but blank fields must not be interpreted as a completed test.

Use the same structure for a replacement valve, altered tube route, changed timer, revised product load or new operating mode. Identify which requirements the change can affect and why. Retesting should follow that impact, not just the easiest movement to observe.

Preserve a concise handover index connecting the requirement register, state table, drawings, component schedule, signal list, configuration backups and verification evidence. Customer-specific records stay private. The public website uses the fictional teaching examples, not an uploaded customer circuit or its production data.

27. Frequently asked engineering questions

What information is required before drawing a pneumatic circuit?

Define the action, load, stroke or travel, timing, supply boundary, quality, operating modes, completion evidence and abnormal-condition behaviour. Identify the mechanical support and safety responsibilities. A component list can follow, but it should not replace these requirements. Unconfirmed settings remain open inputs, not default values. [S1; N1]

Is a pneumatic schematic enough for a controls programmer?

No. The schematic shows functional connections, while the sequence specification explains when actions are permitted and what evidence allows a transition. The programmer also needs modes, signal meanings, timing conventions, fault priorities and restart rules. Drawings, signal lists and state records should agree at the same revision. [N1]

Does a cylinder end switch prove that a workpiece is clamped?

Only if its documented detection condition and the validated machine design support that conclusion. An end switch can be active without establishing contact force or correct workpiece presence. Define exactly what the signal proves and specify additional evidence where the process requires it. Do not rename a position indication “clamp safe” to imply more capability. [S1; N1]

Why can a cylinder be slow when the regulator gauge looks normal?

The gauge may represent a static or upstream condition. Valve flow, tubing, fittings, flow-control settings, exhaust restriction, opposing pressure and mechanical resistance can affect dynamic movement. The requirement should specify pressure and timing at relevant points under the working event, with enough evidence to distinguish these causes.

Is a 5/3 closed-centre valve a secure holding device?

Not by that designation alone. Compressibility and leakage affect stopping and retention. The required duration, permissible displacement, load direction and loss-of-energy conditions must be defined, followed by a suitable engineered arrangement. Do not treat blocked ports as proof that maintenance access or suspended-load retention is safe. [R1]

Should every fault exhaust all the air?

No universal response applies to every machine. Exhausting may remove pneumatic energy but can also change load support or create movement. The required response must follow the actual load arrangement and approved safety design.

Can reset resume the interrupted cycle?

The teaching workflow deliberately separates reset from restart. Reset returns to preparation after the required review; readiness and a new start request precede production. A real machine needs its own approved recovery design, including physical valve and load behaviour. A reset button alone cannot reconcile unknown actuator positions. [N1]

Does low average air use justify small valves and tubes?

No. Short movements can require high interval flow even when average consumption is modest. Record both cycle air quantity and movement-time requirements. Use applicable component and dynamic-sizing evidence for the supply and exhaust paths, rather than selecting solely from the cycle-average flow.

Can an equivalent-looking valve be substituted during maintenance?

Only after the controlled attributes and application are checked. Function, return behaviour, pilot arrangement, flow, exhaust, coil and manual override can differ even when the ports fit. Record the change and verify the affected requirements. Physical interchangeability is not the same as functional equivalence. [S1; N1]