Storm Tank (Engineered Unit)

Storm storage in two compartments, returning its contents to the works at whatever rate the inlet works has spare — the first engineered unit whose control depends on a value another template publishes.

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	storm-tank
Name in the library	Storm Tank (Engineered Unit)
Category	Process Units/engineered
Seeded	version 0.1.0, maturity published
Interface points	8 — inlet, return, spill, fft_spare, tank_full, washwater, power, signals
Asked on drop	16, the same list for a new and an existing tank
Editable setpoints	19
Fault catalogue	32 cases, filtered to what is fitted
Control loops	13 generated graphs

What it models

A storm tank of one or two compartments. In the two-compartment arrangement the cells sit either side of a fixed dividing weir: a small first-flush cell fills to its own crest, then the main cell fills, then the overflow weir spills to the watercourse. Return pumps on a common metered rising main draw the contents back to the works, and washdown jets clean the cells down afterwards.

The drawing it generates carries the tank boundary, the storm inlet through the manual isolation penstock, the two compartments and the dividing weir, the motorised drain penstock between them, the overflow weir with its head transmitter, the return pumps on their metered rising main, the washdown jets, and the control panel with its off-page connections.

The plant model integrated during a run is the two-cell water balance over the dividing weir, the overflow weir's head–discharge behaviour, the return pumps against the system curve across the static range as the tank draws down, the penstocks' travel, the washdown, and the instruments reading all of it.

The port it consumes

This is the unit that makes inter-template values concrete. Its fft_spare port is an in-port: it reads the spare capacity under the consent that the Flow to Full Treatment Control unit publishes, and the return rate is bounded by it. Two things follow, and the unit is explicit about both:

• the published spare is locally corrected before it is used as a setpoint — the figure arrives over a communications register and this unit's own control has a view on it;
• a published value can go stale, so there is a stale-window setpoint, a graph that decides whether the figure still means anything, and a live fact that says which.

Key parameters

Asked on drop

Sixteen, which is the whole budget.

Parameter	Unit	Type
Population equivalent	—	number
Impermeable contributing area	m²	number
Volume sizing rule	—	per head and others
Storm storage volume	m³	number
Compartments	count	1–2
First-flush cell plan area	m²	number
Main cell plan area	m²	number
Tank wall crest above the floor	m	number
Return pumps	count	1–4
Standby	count	0–1
Return control	—	flow / fixed speed
Cleaning	—	jets and others
Spill monitoring	—	level / level and flow
Storm window	—	afternoon / early morning
Overflow weir crest length	m	number
FFT setting (the neighbour's consent, which bounds the return)	l/s	number

The storm window is a genuine configuration axis, not a probe: when in the day the storm arrives changes what the tank has to do. The template carries 83 parameters in total.

Editable setpoints

Nineteen, the largest set of the five units:

Setpoint	Unit
Maximum return rate	l/s
Return loop gain	% per l/s
Return loop integral time · derivative time · Quiescent settlement · Cleaning duration · Published-spare stale window	s
Minimum pump speed · Maximum pump speed	%
Return start level · Return stop level · Cleaning low level · Restart hysteresis	m
…and the remainder, listed in full on the workspace's Parameters view

Control loops

Thirteen generated graphs — the largest set of the five:

Measurement health · FT versus speed-implied flow · Tank level bands · Spare-capacity gate · Storm-tank cycle · Compartment sequencing and penstocks · Return flow control · Return pump duty/standby selector · Return pump control (one per pump) · Spill detection and the EDM record · Washdown jets and proving · Hardwired protection · the outstation

The storm-tank cycle graph is the sequencer: fill into the first cell, quiescent settlement, return to the works, cascade from one cell to the other, wash, then final draw-down. The washdown jets run on one step of that sequence rather than on a clock of their own.

What the outputs mean

Published port values

Port	What it publishes
inlet	The spill it receives at the design peak and at the extreme peak, on the diurnal profile
return	The return rate, with the total head at the worst static lift, and the rising main's bore and material
spill	The overflow weir's design basis and the head standing on it — plus, after a completed run, the event count, duration and volume
fft_spare	The two consumed communications registers (this is the in-port)
tank_full	The tank-full flag and the stored volume
washwater	The wash water demand
power	kW, kVA, amps, essential load, largest start
signals	The size of its signal set

For the reference configuration inlet reads 42.5000 l/s at the design peak and 122.5000 l/s at the extreme; return 18.888889 l/s at 4.532940 m of total head at the worst static, in DN150 ductile iron; spill 122.5000 l/s standing at 0.079668 m of head; washwater 8.000000 l/s; power 4.059335 kW / 4.775688 kVA / 6.893112 A with an essential load of 0.500000 kW; and the signal set 27 DI / 9 DO / 8 AI / 2 AO plus 5 communications registers.

Three of those are run-derived. The spill event count, duration and volume come from a completed run. A freshly placed instance has not run anything, so they fall back to the weir's design basis and to absence.

Overview figures

Storage volume and the sizing rule it came from (with the rule's other form shown alongside), compartments, side water depth against the wall crest, inflow (spill at design and extreme), return duty against the minimum spare, return pumps, empty-down time (the rule's and the achieved), the overflow weir, the spare consumed, cleaning, maximum demand, design findings, control loops.

Live facts during a run

Titled Storm tank: the clock, the unit's mode, the sequence step, the cell levels, the stored volume, the catchment and works-forward flows, the tank inflow, the published spare, the corrected spare against the setpoint, the return rate, each pump's state, the penstocks' positions, the spill, one named unit invariant's live state, and the hardwired circuits.

The calculation charts

Two:

• the fill cascade — stored volume against event size, drawn as the two cells fill in series over the fixed dividing weir: the first cell to its own crest, then the main cell, then the overflow, with the design event, the extreme event, the critical-duration event and the event that first spills all marked;
• the return pump against the system curve across the static range — because the static lift changes as the tank draws down, a single duty point would not describe this duty.

Faults you can inject

Group	Cases
The published spare	lost · frozen at zero · frozen high · over-reported (two storm windows)
Return flow meter FT-x01	signal lost · three low drifts (−8 %, the band edge, −20 %) over two windows · one high drift
Weir head transmitter LT-x02	signal lost · lost with the dry-run float stuck clear · ±0.500 m drift
The return pumps	one lost · both lost · no variable-speed drive (two windows)
Penstocks and weirs	the drain penstock shut · the isolation penstock shut · the dividing weir blocked · the overflow weir blocked (two storm sizes)
Washdown	the wash water does not arrive
Supply	the whole site's, for 2 h, in the storm and in the return
Hardwired	the low-low float stuck operated
Setpoints	the empty-down rule shortened (two windows, and once with an over-reported spare)

A one-compartment tank drops the two first-flush cases, a tank with no cleaning drops the wash-water case, and a single-pump tank drops the pump-selection cases.

Honest limits

• Seeded at published maturity: its configuration matrix passed, so it is visible to every user who passes the plan, tenant and allocation gates.
• Its fft_spare in-port reads a value the flow-to-full-treatment unit publishes, but reading it from a connected upstream instance on the drawing is not built. The figure in force comes from this instance's own parameters and its run. Wiring one placed unit's outlet to another's inlet is slice-2 work.
• Tag builders carry an area placeholder (LT-x01, PST-x01), so two tanks on one drawing will not take distinct tag numbers.
• 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.