3D workshop & DIY
Building an NFT bench: slope, flow rate, manifold
Functional diagram, not to scale.
Slope of at least 2%, 11 to 19 L/h (3 to 5 gal/h) per channel, one valve per line: you set up an NFT bench with a spirit level and a stopwatch.
The pump brings the solution to the high inlet; after that, gravity creates the film. The manifold is simply the distribution header: a large pipe that splits into small tubes, one per channel, each with its own valve.
| Parameter | Benchmark | Source |
|---|---|---|
| Slope | ≥ 2% | Oregon State |
| Flow rate / channel | 11 to 19 L/h (3 to 5 gal/h) | Virginia Tech |
| Spacing, leafy greens | ≈ 20 cm (8 in) | Virginia Tech |
| Length | 1.2 to 3.7 m (≤ 5 m), 4 to 12 ft (≤ 16 ft) | VT / U. Saskatchewan |
| Channel | ≈ 10 cm × 4-5 cm (4 in × 1.5-2 in) | Virginia Tech |
Setting the slope of a channel
- Measure the lengthWrite down L in meters, from the inlet to the outlet.
- Calculate the dropDrop = L × 0.02. For 2 m: 4 cm (1.6 in). For 3 m: 6 cm (2.4 in). (calculator)
- Shim the supportsSpirit level + shims; no low point should create a puddle.
- Test with plain waterThe film should cover the full width and drain out without backing up.
Measuring the flow rate of a channel
- Isolate the outletGraduated container under the channel outlet.
- Time 60 sLiters collected × 60 = flow rate in L/h.
- Compare with 11-19 L/hAdjust the valve, then re-measure the other lines: they affect each other.
Frequently asked questions
What slope for an NFT channel?
At least 2% according to Oregon State, that is a 2 cm drop per meter (about 1/4 in per foot): 4 cm (1.6 in) for a 2 m (6.6 ft) channel, 6 cm (2.4 in) for 3 m (10 ft).
What flow rate in an NFT channel?
Between 11 and 19 liters per hour per channel (3 to 5 gal/h) according to Virginia Tech. Measure it by collecting the water at the outlet for 60 seconds, then adjust the valve on that line.
