This simulator models a double-acting pneumatic piston cylinder — a directional spool routes regulated air to separate cap-end and rod-end chambers, driving a piston rod against an external load, a mechanical return spring, Coulomb friction and hard end stops. Adjust supply pressure, piston geometry, load, spring stiffness, friction and port dynamics, then watch the rod extend, retract or hold.
• A real-time 3D cutaway of the regulator, directional spool, cylinder barrel, piston/seals/rod, cap and rod pneumatic tubing, and the guide carriage/load/spring assembly, with home view, focus-selected-part, toggleable full enclosure, exploded view, auto-rotate, expand and label controls, plus tappable components with callouts numbered to match the companion diagram. • Ten live controls: regulated supply pressure, cap-end piston area, maximum stroke, external extension-opposing load, load spring stiffness, Coulomb friction magnitude, overdamped motion coefficient, port pressure time constant, a four-position directional valve (extend / retract / hold-center-closed / exhaust-both), and an air-supply-available toggle. • Play/pause, single-step (0.1 s) and larger-step (1 s) time controls, plus a playback-speed selector spanning 10× slow motion, real time, 10× faster and 1-minute-per-second. • Eight live metrics: cap chamber pressure, rod chamber pressure, net pneumatic extension force, spring force, net force before friction/end-stop reaction, rod extension, rod velocity and external opposing load. • A Curves & measurements tab with two charts (cap/rod chamber pressure and rod extension over time), the full model equations, and snapshot measurements. • An Experiments tab with four guided scenarios (extend under load, retract, insufficient pressure, strong spring vs. load), a model-verification bench of independent automated checks, and a timestamped event log with a copyable trial report. • A Learn & assess tab with guided lessons (routing air, calculating force, overcoming resistance, respecting stroke limits), a knowledge-check quiz and a written scope/reference statement.
The rod occupies part of the piston's cross-section on the rod-side chamber, so in this representative geometry the rod-side effective area is 75% of the cap-side area. Equal pressure applied to both faces therefore does not produce equal force — extend commands force by pressurizing the larger cap face while venting the rod side, and retract reverses which face is pressurized, so retract force is inherently smaller than extend force at the same supply pressure.
Motion only begins once net force — pneumatic force minus spring force and external load — exceeds the Coulomb friction band; inside that band the rod stays put even though forces are unbalanced on paper. Outside the band, velocity follows an overdamped relationship with the damping coefficient, and travel is clamped between zero and the configured stroke, with a hard stop absorbing the residual force at full extension.
Selecting the center-closed hold position traps air in both chambers rather than exhausting them, and trapped-chamber pressure changes with piston movement following an isothermal compression relationship — it is compliant, not a rigid lock. Port pressures themselves do not jump instantaneously; they follow a first-order response set by the port pressure time constant.
This is an overdamped teaching model with no inertial mass, impact rebound or compressible mass-flow sizing, and closed-center chambers assume a fixed equivalent dead length. Loss of air explicitly vents both chambers, and the external load is modeled as always acting toward retraction, including while the actuator is retracting.
The rod occupies part of the rod-side chamber cross-section, so its effective area is only 75% of the cap-side area in this model. Extending pressurizes the larger cap face; retracting pressurizes the smaller rod-side face, so the same supply pressure produces less force during retraction.
No. Selecting the hold (center-closed) directional-valve position traps air in both chambers, and that trapped pressure changes with piston movement according to an isothermal compression relationship — it acts as a compliant spring, not a solid mechanical lock.
The simulator includes a Coulomb friction band: the rod only moves once net force (pneumatic force minus spring force and external load) exceeds that friction magnitude. The "insufficient pressure" experiment demonstrates a case where available cap-end force is below the opposing load, so the rod remains at its retracted stop regardless of applied pressure.
It is an overdamped model with no piston inertia or impact rebound, no compressible mass-flow port sizing, and a fixed equivalent dead length for closed-center trapped-air calculations. Geometry is representative rather than manufacturer CAD, and the parameters are generic educational values rather than a specific cylinder catalog spec.