This simulator runs two independent spring-return control valves side by side at the same common opening demand — a fail-closed (air-to-open) valve and a fail-open (air-to-close) valve — sharing one regulated air source and a de-energize-to-vent solenoid pair, so you can directly compare how opposite spring/air arrangements respond identically in normal service but diverge on loss of air, loss of power, or a mechanical jam.
• A real-time 3D cutaway of the shared filter-regulator and air receiver, the de-energize-to-vent solenoid pair, the fail-closed valve body with its air-to-open actuator and closing spring, the fail-open valve body with its air-to-close actuator and opening spring, and a travel comparison recorder, with home view, focus-selected-part, toggleable full enclosure, exploded view, auto-rotate, expand and label controls plus tappable numbered components. • Four live controls: a common opening demand shared by both valves, an instrument-air-available toggle, a solenoid-power-available toggle, and a mechanical-fault selector (neither valve jammed / fail-closed stem jammed / fail-open stem jammed). • Play/pause, single-step (0.1 s) and larger-step (1 s) time controls, plus a playback-speed selector from 10× slow motion to 1-minute-per-second. • Dedicated utility actions: remove instrument air and restore instrument air, alongside start/stop trial controls. • Eight live metrics: opening demand, fail-closed valve opening, fail-open valve opening, air-to-open chamber pressure, air-to-close chamber pressure, FC-branch illustrative flow, FO-branch illustrative flow, and an air-and-power-available indicator. • A Curves & measurements tab with two charts (fail-closed vs. fail-open travel, and their respective chamber pressures over time), the full spring-return model equations, and snapshot measurements. • An Experiments tab with four guided scenarios (both track demand, lose instrument air, lose solenoid power, jammed fail-closed valve), 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 (identifying the mechanical bias, distinguishing air actions, removing air or power, verifying actual position), a knowledge-check quiz and a written scope/reference statement.
In normal service, both valves track the same common opening demand and settle at the same travel percentage even though they need opposite pressure commands to get there — the fail-closed (air-to-open) actuator needs pressure proportional to the demand, while the fail-open (air-to-close) actuator needs pressure proportional to one minus the demand. Their chamber pressures differ even while their openings match exactly, which the "both track demand" experiment demonstrates directly.
The divergence only appears once instrument air or solenoid power is lost. This simulator explicitly models a de-energize-to-vent solenoid design, so losing solenoid power produces the identical spring-return endpoints as losing instrument air directly — both pressure targets fall to zero, and each valve's own spring then drives it toward its stored bias: the fail-closed valve toward 0% open, the fail-open valve toward 100% open.
A named "fail action" only describes the intended mechanical bias created by the spring and actuator arrangement — it does not guarantee that the valve will actually reach that position. The jammed fail-closed-valve experiment shows exactly this: with air removed and the fail-closed stem mechanically jammed, that valve remains stuck at its prior 60% opening instead of moving toward 0%, while the unaffected fail-open branch still opens normally. This is why the simulator tracks actual modeled opening, not just the commanded fail action, as the thing to verify.
This is a paired representative first-order model: it uses a 3 bar reference pressure scale, no spring-sizing or process differential-force calculations, a fixed 0.5 s chamber lag and 1 s travel lag, and a linear 20 m³/h full-open flow illustration per branch. The safe fail-position choice itself is application-specific and is not selected or recommended by this comparison.
The fail-closed valve is air-to-open, so its target pressure is proportional to the opening demand. The fail-open valve is air-to-close, so its target pressure is proportional to one minus the opening demand. Both reach the same travel percentage in normal service, but their actuator chamber pressures are different — and in the opposite direction — for that same demand.
Not in this model. The simulator explicitly uses a de-energize-to-vent solenoid pair, so a loss of solenoid power vents the actuator chambers exactly like a direct loss of instrument air — both pressure targets drop to zero and each valve moves toward its spring-biased fail position. Other solenoid designs could behave differently, which the scope notes explicitly.
No. The jammed fail-closed-valve experiment shows a mechanically jammed stem holding the valve at its prior opening even after instrument air is removed, while the unaffected fail-open valve still moves normally. Intended fail action is a design bias, not a guarantee — actual final-element position must be verified independently.
It is a paired first-order representative model with a fixed 0.5 s chamber lag and 1 s travel lag, a 3 bar reference actuator pressure scale, and a linear 20 m³/h full-open flow estimate per branch. It excludes spring sizing, process differential-force calculations, and does not select or recommend which fail position is correct for a given application.