A P-trap cutaway beneath a basin shows the water seal between the tailpiece and the drain arm. Set the seal head, choose a positive or negative drain-side pressure, and repeat a three-second pulse to watch the two water surfaces displace and see when the ideal seal-head capacity is exceeded.
• A real-time 3D view with numbered, clickable parts: basin and tailpiece; p-trap shell cutaway; water seal and displaced surfaces; drain arm and sewer-side pressure; potential gas path. Scene tools include home view, focus-selected-part, auto-rotate, expand and show/hide labels, and drag-to-orbit with pinch-to-zoom. • Experiment controls: available seal head (20–80 mm water); drain-side differential pressure (-1000–1000 Pa); repeat a three-second pressure pulse, plus a show flow/process markers toggle, pause/resume, single-step buttons (0.1 s and 1 s), a playback-speed selector and a restart experiment action. • Live readouts: seal head; drain-side differential; equivalent surface-height difference; seal-head capacity; capacity minus pressure magnitude; capacity exceeded indicator. A model response curve is drawn beside the 3D view and updates as you change controls. • A Curves & measurements tab with two live charts, the model equations as written in the simulator and snapshot readouts; an Experiments tab with 2 guided presets (within capacity; challenge the seal) plus a model-verification bench, timestamped event log and copyable trial report. • A Learn & assess tab with 3 lessons (follow the system; connect the measurements; interpret the model), a 2-question knowledge check with reset, and a written model-scope statement.
The trap behaves like a U-tube: a pressure difference ΔP between the drain side and the room moves the water until the height difference Δh satisfies ΔP = ρgΔh. About 50 mm of water corresponds to roughly 490 Pa. With equal-area limbs, each surface moves approximately half the height difference, which the cutaway animates.
Seal-head capacity is ρg times the seal head, and the pressure margin is that capacity minus the magnitude of the applied pressure. The simulator shows the equivalent surface-height difference and a capacity-exceeded indicator.
A 200 Pa difference stays within a 50 mm seal, while a larger challenge gives a negative margin and shows the potential gas path warning. After each pulse the model returns to the specified starting seal.
This is a quasi-static comparison. Once capacity is exceeded, the model flags lost protection; it does not predict irreversible siphon loss, evaporation, splash, sewer-gas concentration or two-phase bubbling. Dimensions are enlarged for explanation, and this is a generic educational model, not a code-compliance tool.
It holds a small volume of water in the drain path. That water seal blocks sewer gas from entering the room while letting wastewater pass.
About 490 Pa, because pressure equals ρ times g times the seal head.
Positive pressure pushes the drain-side surface down and the room side up; negative pressure (suction) does the opposite. Either can challenge the seal if it is large enough.
No. It flags when the ideal capacity is exceeded but does not model seal loss over time, splashing or bubbling.