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Flow Balancing Tank (Engineered Unit)
A flow-equalisation vessel: it stores the peak and passes a controlled rate forward, so the works downstream sees a flatter flow than the catchment delivers.
Which simulation? Running this unit uses the client-side, PLC-style scan simulation in your browser, not the server-side biokinetic process simulation. See Which "simulation" this section is about.
| Slug | flow-balancing-tank |
| Name in the library | Flow Balancing Tank (Engineered Unit) |
| Category | Process Units/engineered |
| Seeded | version 0.1.0, maturity published |
| Interface points | 5 — inlet, outlet, overflow, signals, power |
| Asked on drop | 10 for a new vessel, 15 for an existing one |
| Editable setpoints | 11 |
| Fault catalogue | 21 cases, filtered to what is fitted |
| Control loops | 8 generated graphs |
What it models
A balancing vessel, rectangular or circular, with:
- a gravity or pumped inflow;
- an outlet device — a modulating aperture (penstock), a modulating valve, or transfer pumps — through which the pass-forward is held;
- an overflow weir to a watercourse or to a storm destination, with its own level switch;
- mixers (0–4) or an aeration grid, to keep the contents from going septic;
- an optional washdown set;
- the instrument set: level transmitter, two flow meters, position feedback, a quality probe and floats; and the control panel.
The plant model integrated during a run is the vessel's water balance — inflow against the pass-forward the outlet device actually passes at the head available — plus the device's travel, the mixers, the overflow, and the instruments reading all of it.
What it derives rather than asks
This is the unit that makes the "engineered" distinction concrete, because four of its governing numbers are derived, not typed:
| Derived | From |
|---|---|
| Dry weather flow | the population equivalent, the rule set's per-head allowance and infiltration fraction, and any trade effluent. A non-zero override wins, and the calculation sheet then labels the row as an override rather than a derivation. |
| The diurnal profile | a rule-set shape of 24 hourly factors. A project's own factors can be injected, and a profile that does not sum to 24 is refused rather than silently rescaled — every flow derived from dry weather flow would otherwise be quietly wrong. |
| The design storm | the rational method on the impermeable area, the rule set's runoff coefficient and the design rainfall intensity, shaped as a symmetrical triangular hydrograph. The rainfall intensity is an input; the storm is never typed. |
| The emergency gravity capacity | the outlet aperture and the outlet main in series, consuming the whole head available at top water level. This is the number that exposes the shock-load risk downstream — a template that let you type it would be hiding that risk. |
Key parameters
Asked on drop
| Parameter | Unit | Type | Asked |
|---|---|---|---|
| Design basis | — | new / existing | always |
| Population equivalent | — | number | always |
| Impermeable contributing area | m² | number | always |
| Design rainfall intensity | mm/h | number | always |
| Downstream accepted flow | l/s | number | always |
| Plan shape | — | rectangular / circular | always |
| Inflow arrangement | — | gravity / pumped | always |
| Outlet device | — | aperture / valve / transfer pumps | always |
| Mixers | count | 0–4 | always |
| Base pass-forward | l/s | number | always |
| Internal length | m | number | if existing |
| Internal width | m | number | if existing |
| Internal diameter | m | number | if existing |
| Top water level above the floor | m | number | if existing |
| Outlet main internal diameter | mm | number | if existing |
The template carries 73 parameters in total; the rest keep their defaults and are visible on the workspace's Parameters view.
Editable setpoints
| Setpoint | Unit |
|---|---|
| Minimum operating level · Modulation band low · Modulation band high · High level alarm | m |
| Base pass-forward · Maximum modulated pass-forward | l/s |
| Position deviation delay · Mixer run-on · Spill reporting delay | s |
| High-high safe-maximum travel | % |
| Dissolved oxygen low limit | mg/l |
Control loops
Eight generated graphs:
Level and volume · Pass-forward control · Storm and fill · Empty-down and recovery · Mixing · Anti-septicity · Floats (hardwired) · the outstation
What the outputs mean
Published port values
| Port | What it publishes |
|---|---|
inlet | Dry weather flow, design peak, and the design storm volume |
outlet | The designed pass-forward, the derived emergency gravity capacity at top water level, the head available at the minimum operating level and at top water, and the outlet main's bore and material |
overflow | The spill route |
signals | The size of its signal set |
power | The electrical load |
For the reference configuration the inlet reads 23.4375 l/s dry weather flow, 103.4375 l/s peak and 288.0 m³ of storm volume; the outlet 25.0 l/s pass-forward with an emergency capacity of 59.1542 l/s at top water, 1.1000 m of head at the minimum operating level and 3.5000 m at top water, in DN200 ductile iron; and the signal set 17 DI / 4 DO / 5 AI / 1 AO.
Overview figures
Outlet device, number of mixers, working volume, containment volume, pass-forward (base and maximum), design findings, control loops.
Live facts during a run
Titled Vessel: the clock, the level with the transmitter's reading, the stored volume and percent full, in / out / spill flows, the outlet device's reading, the mixers' state, the current retention time, and the volume spilled.
Trend panels
Three: level (with the LT reading dashed, and reference lines at the wall crest, LSHH, the modulation band and LSLL), flow (inflow and pass-forward), and mixers running.
The calculation chart
The Rippl mass curve — cumulative inflow minus a constant pass-forward, clipped at zero. This is exactly the construction the calculation sheet's required-balancing-volume row cites, so you can see the shape the number came from. The live inflow / pass-forward / spill trend is deliberately not duplicated here; the Simulate view already draws it, live.
Faults you can inject
| Group | Cases |
|---|---|
| Level transmitter | fails · frozen · drifts +1 m · drifts −1 m |
| Floats | LSHH fails / stuck on · LSLL fails / stuck on |
| Pass-forward meter | fails · reads zero · reads ×2 |
| Outlet device | fails closed · fails open · sticks mid-travel · throttled to 25 % |
| Position feedback | lost |
| Mixers | a mixer trips · a mixer fails to start |
| Boundary | downstream refuses flow · supply failure · downstream halves the accepted flow |
A vessel with no level transmitter is four cases shorter; one with a valve outlet drops the four penstock cases.
One case is injected differently, and says so. "Downstream halves the accepted flow" is a partial refusal, and the plant model has no flag for a partial refusal — only a total one. Rather than change the frozen physics, that case is injected where the refusal is actually declared: the setpoints the control clamps to. This is reported as a missing plant mechanism, not presented as a modelling choice.
Honest limits
- Seeded at
publishedmaturity: its configuration matrix passed, so it is visible to every user who passes the plan, tenant and allocation gates. - Its tag builders carry an area placeholder (
LT-x01,PST-x01) — there is no area parameter on this unit yet, so two vessels on one drawing will not take distinct tag numbers the way the pumping station's do. - The run verdict and the design findings are shown on the workspace's Validation view.
- Nobody has recorded watching this unit run in a browser.