| Scenario | Qavg (m³/day) | Peak factor | Eq time (h) | Detention (h) | Safety (%) | Design volume (m³) | Total w/ freeboard (m³) |
|---|---|---|---|---|---|---|---|
| Municipal lift station | 1,200 | 2.5 | 4 | 6 | 10 | 330.00 | 379.50 |
| Industrial batch discharge | 800 | 3.0 | 6 | 8 | 15 | 632.50 | 727.38 |
| Small facility stabilization | 250 | 2.0 | 3 | 10 | 5 | 109.38 | 125.78 |
- Average flow rate: Qavg(m³/hr) = Qavg(m³/day) ÷ 24
- Peak flow rate: Qpeak(m³/hr) = Qpeak(m³/day) ÷ 24
- Peak shaving volume: Vpeak = max(0, (Qpeak − Qavg) × teq)
- Detention-based volume: Vdet = Qavg × tdet
- Base volume: Vbase = max(Vpeak, Vdet)
- Design volume with safety: Vdesign = Vbase × (1 + Safety%)
- Total with freeboard: Vtotal = Vdesign × (1 + Freeboard%)
- Enter the average daily inflow rate for the system.
- Select a peak definition using a factor or a known peak flow.
- Set equalization time to match the expected peak duration.
- Set detention time for operational stability and mixing needs.
- Add safety and freeboard to reflect uncertainty and headspace.
- Select a tank shape and usable water depth for dimensions.
- Click Calculate, then export results to CSV or PDF.
Design intent and hydraulics
An equalization tank reduces shock loads by smoothing inflow variability before downstream treatment. This calculator compares a peak shaving check against a detention based check, then applies safety and freeboard allowances. Use it during concept design to quickly screen whether the governing volume is driven by short peaks or by minimum holding time requirements.
Flow profile and assumptions
Start with a representative average daily flow and a defensible peak definition. If you only know a peak factor, the tool derives peak flow from the average. If you have measured peak flow, enter it directly. Equalization time should reflect the expected peak duration, while detention time reflects the minimum operational residence needed for stable pumping, odor control, or process buffering.
Operational mixing considerations
Mixing and aeration strategy influence the practical usable volume. Provide a realistic usable water depth that accounts for mixer submergence, pump suction clearance, and maintenance access. Detention volumes can be conservative when large batch discharges exist; in those cases, review hourly profiles and verify whether controlled dosing, timed pumping, or upstream scheduling can reduce required storage. Where industrial wastewater is present, document pH range, temperature, and solids content, because these affect material selection, ventilation needs, and cleaning frequency, which can directly change the practical freeboard and maintenance volume.
Dimensional checks and layout
Once the design volume is selected, the calculator proposes preliminary plan dimensions. Rectangular sizing uses a length to width ratio that supports hydraulic circulation and equipment placement. Cylindrical sizing uses an equivalent plan area to estimate diameter. Treat these outputs as starting points; confirm structural wall thickness, seismic and uplift checks, and headloss through inlet and outlet arrangements.
Documentation and handover
Exported CSV and PDF outputs help capture assumptions, inputs, and derived values for reviews. Include site constraints, target operating level, and future growth notes alongside the results. For final design, validate the selected method with monitoring data, check pump cycling limits, and coordinate instrumentation for level control, alarms, and bypass management.
FAQs
Which volume should I adopt for design?
Use the larger of the peak shaving volume and the detention based volume. That choice reflects whether short peaks or minimum residence time controls. Apply safety and freeboard after selecting the governing base volume.
How do I select equalization time?
Set equalization time to the typical duration of peak inflow or batch discharge. Use monitoring or operational knowledge. If unsure, start with a conservative window and run sensitivity checks to see how strongly volume changes.
What is the difference between safety factor and freeboard?
Safety factor increases usable design volume to cover uncertainty, growth, and model simplifications. Freeboard adds headspace above the operating water level for wave action, instrumentation tolerances, and upset conditions without increasing usable mixing volume.
Does the calculator replace a detailed flow profile study?
No. It provides planning level sizing using simplified checks. Final designs should use hourly or subhourly influent data, confirm pump control strategy, and review hydraulic constraints at inlet, outlet, and bypass structures.
How are preliminary dimensions estimated?
The tool divides design volume by usable depth to get plan area. Rectangular tanks use your length to width ratio to compute length and width. Cylindrical tanks compute an equivalent diameter from the plan area.
What other factors can increase required volume?
Odor control targets, emergency storage, equipment downtime, cleaning allowances, and industrial wastewater characteristics can raise practical volume. Confirm minimum pump submergence, mixer clearance, and access requirements so the usable depth and freeboard assumptions remain realistic.
Design intent and hydraulics
An equalization tank reduces shock loads by smoothing inflow variability before downstream treatment. This calculator compares a peak shaving check against a detention based check, then applies safety and freeboard allowances. Use it during concept design to quickly screen whether the governing volume is driven by short peaks or by minimum holding time requirements.
Flow profile and assumptions
Start with a representative average daily flow and a defensible peak definition. If you only know a peak factor, the tool derives peak flow from the average. If you have measured peak flow, enter it directly. Equalization time should reflect the expected peak duration, while detention time reflects the minimum operational residence needed for stable pumping, odor control, or process buffering.
Operational mixing considerations
Mixing and aeration strategy influence the practical usable volume. Provide a realistic usable water depth that accounts for mixer submergence, pump suction clearance, and maintenance access. Detention volumes can be conservative when large batch discharges exist; in those cases, review hourly profiles and verify whether controlled dosing, timed pumping, or upstream scheduling can reduce required storage. Where industrial wastewater is present, document pH range, temperature, and solids content, because these affect material selection, ventilation needs, and cleaning frequency, which can directly change the practical freeboard and maintenance volume.
Dimensional checks and layout
Once the design volume is selected, the calculator proposes preliminary plan dimensions. Rectangular sizing uses a length to width ratio that supports hydraulic circulation and equipment placement. Cylindrical sizing uses an equivalent plan area to estimate diameter. Treat these outputs as starting points; confirm structural wall thickness, seismic and uplift checks, and headloss through inlet and outlet arrangements.
Documentation and handover
Exported CSV and PDF outputs help capture assumptions, inputs, and derived values for reviews. Include site constraints, target operating level, and future growth notes alongside the results. For final design, validate the selected method with monitoring data, check pump cycling limits, and coordinate instrumentation for level control, alarms, and bypass management.
FAQs
Which volume should I adopt for design?
Use the larger of the peak shaving volume and the detention based volume. That choice reflects whether short peaks or minimum residence time controls. Apply safety and freeboard after selecting the governing base volume.
How do I select equalization time?
Set equalization time to the typical duration of peak inflow or batch discharge. Use monitoring or operational knowledge. If unsure, start with a conservative window and run sensitivity checks to see how strongly volume changes.
What is the difference between safety factor and freeboard?
Safety factor increases usable design volume to cover uncertainty, growth, and model simplifications. Freeboard adds headspace above the operating water level for wave action, instrumentation tolerances, and upset conditions without increasing usable mixing volume.
Does the calculator replace a detailed flow profile study?
No. It provides planning level sizing using simplified checks. Final designs should use hourly or subhourly influent data, confirm pump control strategy, and review hydraulic constraints at inlet, outlet, and bypass structures.
How are preliminary dimensions estimated?
The tool divides design volume by usable depth to get plan area. Rectangular tanks use your length to width ratio to compute length and width. Cylindrical tanks compute an equivalent diameter from the plan area.
What other factors can increase required volume?
Odor control targets, emergency storage, equipment downtime, cleaning allowances, and industrial wastewater characteristics can raise practical volume. Confirm minimum pump submergence, mixer clearance, and access requirements so the usable depth and freeboard assumptions remain realistic.