- Read a pump curve at the total dynamic head of your installation, not at the nameplate flow.
- Translate what NFT channels and flood tables need into duty, flow, fill time and drain-back requirements.
- Produce a written spec sheet that a listing either meets or does not.
Delivered-flow calculator
Flow L/h = collected litres ÷ seconds × 3,600. Nominal turnovers/h = flow ÷ volume.
Installed flow (L/hour): 360; Nominal turnovers/hour: 3; One inventory equivalent (minutes): 20
Use installed delivery at the normal head. Turnover arithmetic does not verify oxygen, uniform mixing or treatment capacity.
01 / The nameplate is not the delivered flow
The flow on a pump’s box is usually quoted at little or no lift through an open outlet. NDSU AE1057 defines total dynamic head (TDH) as the sum of the total static head, total friction head and pressure head: static head is the vertical distance the pump must lift the water, and friction head is the energy loss as water flows through pipe networks, in straight pipe, fittings and valves, around corners and where pipes change size. Here TDH is lift plus friction.
Kansas State L886 gives the rule: a given pump can produce only a certain flow for a given head, and vice versa. Read the manufacturer’s curve at your TDH; a listing with only a maximum flow and a maximum head has not specified the pump. Then measure.
Reading: Irrigation Water Pumps (AE1057) ↗ · Reading Pump and Engine Performance Curves (L886) ↗
02 / What an NFT channel asks of the pump
Oregon State EM 9457 describes NFT as a thin, continuous film of solution and asks for a minimum 2% slope in horizontal channels to keep it flowing. It prints no flow rate per channel; neither does UKY CCD-SP-20, which describes a continuously running pump and notes that a downward slope reduces stress on the pump. Set channel flow by watching the floor for ponding and measuring what reaches the last inlet.
Oklahoma State HLA-6442 notes that NFT systems have a constant flow of nutrient solution, so no timer is required for the submersible pump: continuous duty is the first line on the sheet. EM 9457 calls backups for power and pumps crucial because power loss or pump failure can lead to immediate plant wilting. Specify total flow at the manifold’s TDH with margin, one balancing valve per branch, and a spare with the same outlet fitting.
Reading: Hydro hints: Nutrient film technique ↗ · Irrigation in Hydroponic Systems: An Illustrated Overview (CCD-SP-20) ↗ · Hydroponics (HLA-6442) ↗
03 / What a flood table asks of the pump
EM 9458 lists flood trays, a nutrient reservoir, a pump and a timer; the timer controls the pump, which floods the trays, and the solution then drains back into the reservoir. Its timing plan is to flood to about an inch below the top of the media, drain once the media is fully soaked, and flood again before the media begins to dry out and contract. Mechanical plug-in timers switch in fixed segments, so the pump must reach the flood line within the shortest on-time your timer allows, starting from the lowest reservoir level. Size from the flood volume you measured by drawdown.
Drain-back is the half of the cycle the pump can block. CCD-SP-20 describes the pump running until the channel is filled and stopping, with a drain valve that stays closed through the soak and then opens to let the solution flow back into the tank. Many small tables have no such valve: the return passes back through the fill fitting and the pump itself, and a built-in check valve can hold water in the tray. Ask whether the pump passes reverse flow when off, or fit a separate drain, and test it under the timer before planting.
Reading: Hydro hints: Ebb and flow ↗ · Irrigation in Hydroponic Systems: An Illustrated Overview (CCD-SP-20) ↗
04 / Intake, outlet, materials and heat
An intake screen keeps roots, fines and algae out of the impeller but adds friction the curve does not include, more as it loads; choose one you can rinse without tools. Match the outlet to your tubing: every reducer and elbow after it is friction head. List every wetted material and reject bare steel, brass or zinc, which can corrode in an acidic salt solution.
A submerged motor sheds its heat into the reservoir. EM 9457 says shallow NFT channels are sensitive to ambient temperature changes and lists larger stock tanks among its mitigations, so log solution against room temperature with the pump on and off, and prefer the lower-wattage pump whose curve still meets your head.
05 / Duty cycle, timers and electrical safety
NFT wants a pump rated for continuous operation. A flood table asks for many starts a day, so look for timer-control suitability and any minimum on-time. EM 9458’s requirement for a reliable timer applies to the pair: a timer rated for the pump’s starting current and a pump that starts every cycle.
Electrical safety here is general practice, not a rule from the cited publications: supply pump and timer through ground-fault protection (GFCI/RCD); keep the plug and every cord connection above the water line with a drip loop; route the cord clear of chafe and the drain path; switch off and unplug before reaching into the solution. Local electrical code and the product label govern; check local rules.
Reading: Hydro hints: Ebb and flow ↗
06 / Write the spec sheet, then shop
Fill the sheet before you look at any product, then compare listings to the sheet rather than to each other.
- Measure static lift from the lowest working reservoir level to the highest inlet or flood fitting.
- List tubing, fittings and screen as the friction allowance; you will measure it, not compute it.
- Set required flow: NFT, channel delivery that kept a film × channels plus throttling margin; table, flood volume ÷ fill time inside one timer increment.
- Set duty, decide drain-back, and write outlet size, wetted materials, wattage ceiling and electrical requirements.
- Read listings last: reject any without a curve and read survivors at your TDH. After installation, measure delivered flow, clean and loaded, as the baseline.
| Criterion | What to write down | Where it comes from |
|---|---|---|
| Required flow | NFT: L/hour at the manifold. Table: L/min to fill in one timer increment. | Channel delivery × channels; flood volume ÷ fill time. |
| Total dynamic head | Lift to the highest outlet plus a friction allowance. | NDSU AE1057; tape measure and fittings count. |
| Curve point | Flow at your TDH from the curve. | Manufacturer curve; nameplate maximum not accepted. |
| Duty and drain-back | Continuous or timer-cycled; reverse flow when off, or a separate drain. | HLA-6442 (no timer for NFT; timer-cycled submerged pump for ebb and flow); your own drain test under the timer. |
| Intake, outlet, materials | Screen access; outlet size; every wetted material. | Fittings list; manufacturer materials statement. |
| Heat and electrical | Rated watts; GFCI/RCD, drip loop, cord run. | Nameplate; general practice; local rules. |
| Spare | Identical pump or same outlet fitting. | EM 9457 backup guidance. |
FIELD QUESTIONYour flood table draws 36 L to the flood line with pots in place. You want the fill done in 5 minutes of a 15-minute timer period; static lift is 0.9 m. A candidate is listed at 1,500 L/h maximum and its curve reads 720 L/h at 1.0 m. Does it meet the sheet?
Required flow: 36 L ÷ 5 min = 7.2 L/min, or 432 L/h. Lift is 0.9 m and the elbow, fitting and screen add friction, so 1.0 m is a fair reading point. At 720 L/h the fill takes 36 ÷ 720 × 60 = 3 minutes, inside the target with margin for screen loading; the nameplate would have predicted 1.4 minutes. Accept provisionally, confirm drain-back, then time the real fill.
Reading: Irrigation Water Pumps (AE1057) ↗ · Hydroponics (HLA-6442) ↗ · Hydro hints: Ebb and flow ↗ · Hydro hints: Nutrient film technique ↗
Parts & buying criteria
Build your own parts & cost worksheet →
Showing ebb and flow. Quantities describe the teaching model. Specify real working volume, support, fittings and instruments for your installation.
01Nutrient reservoir1 · illustrated quantity+
Stores the measured nutrient solution beneath or beside the growing area.
Inspect: Compare the surface with the pump intake or lower roots; freeboard is deliberate.
Maintain: Record level before refilling, keep light out and verify temperature, EC and pH.
Opaque, cleanable, intended-use container with volume marks and service access.
Check size, materials and operating conditions with your chosen supplier before ordering.02Pump & supply1 · illustrated quantity+
Moves nutrient solution from the reservoir to the growing area.
Inspect: Trace installed lift and branching; the pump label does not prove delivered flow.
Maintain: Measure output after service and inspect intake, filter and minimum water level.
Pump curve matched to installed head, required pressure and service needs.
Check size, materials and operating conditions with your chosen supplier before ordering.03Growing tray1 · illustrated quantity+
Contains supported media pots above the lower reservoir.
Inspect: Inspect the flood level, pot bases and accessible drain position.
Maintain: Verify full drainage and inspect moisture in representative pots.
Rigid cleanable tray with independent overflow and adequate support.
Check size, materials and operating conditions with your chosen supplier before ordering.04Root-zone mediumFor illustrated containers · illustrated quantity+
Stores moisture and air around the roots in the illustrated containers.
Inspect: Compare the medium surface with irrigation and drainage.
Maintain: Inspect wetting at several depths; prevent fines from reaching drains and emitters.
Prepared, stable grade matched to the irrigation method and crop.
Check size, materials and operating conditions with your chosen supplier before ordering.05Drain & overflow1 · illustrated quantity+
Returns drainage to the reservoir and provides a controlled high-water route.
Inspect: Follow the full slope and look for the separate high-level opening.
Maintain: Test pump-off drain-back and keep roots and medium out of the outlet.
Accessible fittings and verified capacity under normal and fault conditions.
Check size, materials and operating conditions with your chosen supplier before ordering.Evidence beside the lesson.
Source checks: September 2026. The geometry, inspection exercises and worksheets are original teaching material. The named organizations have not endorsed or reviewed this site.
Published recipe rates and planning ranges retain their source context. Calculator equations are accounting tools; they do not predict uptake, yield, toxicity or safe stocking. Model dimensions, water speeds, roots and fish counts are illustrative. Verify species, crop, source water and product labels for a real system.
- North Dakota State University ExtensionIrrigation Water Pumps (AE1057) ↗
Definition of total dynamic head as the sum of total static head, total friction head and pressure head; static head as the vertical distance the pump must lift the water; friction head as energy loss in pipe networks, occurring in straight pipe, fittings and valves, around corners and where pipe size changes; pump curves plotted as flow rate against TDH and used to select a pump once the desired flow rate and TDH are known.
- Kansas State University Research and ExtensionReading Pump and Engine Performance Curves (L886) ↗
The head–capacity curve: a given pump can produce only a certain flow for a given head, and vice versa; total dynamic head including pumping lift, elevation change, friction losses and system operating pressure. Written for irrigation pumping plants.
- Oregon State University ExtensionHydro hints: Nutrient film technique ↗
Channel slope, root space and flow continuity.
- University of Kentucky Center for Crop DiversificationIrrigation in Hydroponic Systems: An Illustrated Overview (CCD-SP-20) ↗
Illustrated overview of DWC, NFT and flood-and-drain, including drip-fed individual containers (bags or buckets) draining to a shared gutter; cycle frequency and soak time adjusted with crop size and conditions.
- Oklahoma State University ExtensionHydroponics (HLA-6442) ↗
System categories and recirculating nutrient delivery.
- Oregon State University ExtensionHydro hints: Ebb and flow ↗
Flood-and-drain operation; irrigation depends on media and plants.
The next useful connections.
From reservoir to roots.
Follow a nutrient film system from its first inlet to its last root. Learn what each part does, what to inspect, and how the pieces work together.
12 min + model exploration →Growing methodsEbb and flow: flood, drain, observe
Build a flood table, size its working water inventory and tune irrigation from the medium’s actual wetting and drying.
6 min + guided practice →Growing methodsDrip and Dutch buckets: deliver to every plant
Design a serviceable bucket system for larger crops, then measure irrigation uniformity and drainage.
Interactive tool · 6 min + guided practice →Equipment & layoutPumps, head and delivered flow
Choose a pump from its operating curve and verify every branch under real installation conditions.
Interactive tool · 6 min + guided practice →Buying guidesChoosing an air pump for DWC and aquaponics: DO, depth, backup
An air pump is bought against a dissolved-oxygen reading at your diffuser depth, not against the litres per minute printed on its box.
8 min + guided practice →